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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	MTB
Entity Registrant Name	M&T BANK CORP
Entity Central Index Key	0000036270
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		150,515,367

Consolidated Balance Sheet (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 1,368,252	$ 1,320,549
Interest-bearing deposits at banks	6,306,484	5,000,638
Trading account	170,516	323,867
Investment securities (includes pledged securities that can be sold or repledged of $488,200 at September 30, 2017; $1,203,473 at December 31, 2016)
Available for sale (cost: $11,369,815 at September 30, 2017; $13,338,301 at December 31, 2016)	11,416,824	13,332,072
Held to maturity (fair value: $3,247,954 at September 30, 2017; $2,451,222 at December 31, 2016)	3,242,124	2,457,278
Other (fair value: $414,978 at September 30, 2017; $461,118 at December 31, 2016)	414,978	461,118
Total investment securities	15,073,926	16,250,468
Loans and leases	88,171,225	91,101,677
Unearned discount	(246,091)	(248,261)
Loans and leases, net of unearned discount	87,925,134	90,853,416
Allowance for credit losses	(1,013,326)	(988,997)
Loans and leases, net	86,911,808	89,864,419
Premises and equipment	656,713	675,263
Goodwill	4,593,112	4,593,112
Core deposit and other intangible assets	78,614	97,655
Accrued interest and other assets	5,242,379	5,323,235
Total assets	120,401,804	123,449,206
Liabilities
Noninterest-bearing deposits	33,111,246	32,813,896
Savings and interest-checking deposits	52,936,615	52,346,207
Time deposits	7,233,518	10,131,846
Deposits at Cayman Islands office	232,014	201,927
Total deposits	93,513,393	95,493,876
Federal funds purchased and agreements to repurchase securities	200,768	163,442
Accrued interest and other liabilities	1,791,946	1,811,431
Long-term borrowings	8,577,645	9,493,835
Total liabilities	104,083,752	106,962,584
Shareholders' equity
Preferred stock, $1.00 par, 1,000,000 shares authorized; Issued and outstanding: Liquidation preference of $1,000 per share: shares 731,500 at September 30, 2017 and December 31, 2016; Liquidation preference of $10,000 per share: 50,000 shares at September 30, 2017 and December 31, 2016	1,231,500	1,231,500
Common stock, $.50 par, 250,000,000 shares authorized, 159,819,892 shares issued at September 30, 2017; 159,945,678 shares issued at December 31, 2016	79,910	79,973
Common stock issuable, 27,019 shares at September 30, 2017; 32,403 shares at December 31, 2016	1,827	2,145
Additional paid-in capital	6,598,048	6,676,948
Retained earnings	9,909,415	9,222,488
Accumulated other comprehensive income (loss), net	(247,915)	(294,636)
Treasury stock — common, at cost — 8,555,636 shares at September 30, 2017; 3,764,742 shares at December 31, 2016	(1,254,733)	(431,796)
Total shareholders’ equity	16,318,052	16,486,622
Total liabilities and shareholders’ equity	$ 120,401,804	$ 123,449,206

Consolidated Balance Sheet (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Pledged securities that can be sold or repledged	$ 488,200	$ 1,203,473
Investment securities, available for sale, amortized cost	11,369,815	13,338,301
Investment securities, held to maturity, fair value	3,247,954	2,451,222
Other, fair value	$ 414,978	$ 461,118
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	1,000,000	1,000,000
Common stock, par value	$ 0.50	$ 0.50
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	159,819,892	159,945,678
Common stock issuable, shares	27,019	32,403
Treasury stock, shares	8,555,636	3,764,742
Series A and Series C [Member]
Preferred stock, shares issued	731,500	731,500
Preferred stock, shares outstanding	731,500	731,500
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Series D Preferred Stock [Member]
Preferred stock, shares issued		50,000
Preferred stock, shares outstanding		50,000
Preferred stock, liquidation preference per share		$ 10,000

Consolidated Statement of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest income
Loans and leases, including fees	$ 953,662	$ 871,345	$ 2,776,340	$ 2,602,208
Investment securities
Fully taxable	87,937	84,893	276,057	274,092
Exempt from federal taxes	345	623	1,154	2,081
Deposits at banks	14,970	12,354	39,345	33,684
Other	296	300	760	905
Total interest income	1,057,210	969,515	3,093,656	2,912,970
Interest expense
Savings and interest-checking deposits	37,714	24,067	93,891	60,906
Time deposits	13,992	27,886	49,293	79,075
Deposits at Cayman Islands office	310	204	856	578
Short-term borrowings	554	169	1,148	3,474
Long-term borrowings	47,506	58,849	138,874	174,814
Total interest expense	100,076	111,175	284,062	318,847
Net interest income	957,134	858,340	2,809,594	2,594,123
Provision for credit losses	30,000	47,000	137,000	128,000
Net interest income after provision for credit losses	927,134	811,340	2,672,594	2,466,123
Other income
Mortgage banking revenues	96,737	103,747	267,592	275,193
Service charges on deposit accounts	109,356	107,935	319,589	314,212
Trust income	124,900	118,654	371,712	350,181
Brokerage services income	14,676	15,914	48,677	48,190
Trading account and foreign exchange gains	7,058	12,754	24,833	33,434
Gain (loss) on bank investment securities		28,480	(17)	28,748
Other revenues from operations	106,702	103,866	334,704	310,579
Total other income	459,429	491,350	1,367,090	1,360,537
Other expense
Salaries and employee benefits	399,089	399,786	1,247,851	1,230,246
Equipment and net occupancy	75,558	75,263	223,721	225,165
Outside data processing and software	45,761	42,878	134,637	128,402
FDIC assessments	23,969	28,459	78,149	76,054
Advertising and marketing	17,403	21,996	49,837	66,063
Printing, postage and supplies	8,732	8,972	27,397	30,865
Amortization of core deposit and other intangible assets	7,808	9,787	24,341	33,524
Other costs of operations	227,705	165,251	558,579	488,063
Total other expense	806,025	752,392	2,344,512	2,278,382
Income before taxes	580,538	550,298	1,695,172	1,548,278
Income taxes	224,615	200,314	609,269	563,735
Net income	355,923	349,984	1,085,903	984,543
Net income available to common shareholders
Basic	335,801	326,992	1,025,011	915,670
Diluted	$ 335,804	$ 326,998	$ 1,025,023	$ 915,686
Net income per common share
Basic	$ 2.22	$ 2.10	$ 6.71	$ 5.82
Diluted	2.21	2.10	6.69	5.80
Cash dividends per common share	$ 0.75	$ 0.70	$ 2.25	$ 2.10
Average common shares outstanding
Basic	151,347	155,493	152,866	157,336
Diluted	151,691	156,026	153,293	157,843

Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Partners Capital [Abstract]
Net income	$ 355,923	$ 349,984	$ 1,085,903	$ 984,543
Other comprehensive income, net of tax and reclassification adjustments:
Net unrealized gains (losses) on investment securities	18,258	(17,133)	33,834	127,331
Cash flow hedges adjustments	(1,120)	(23)	(2,098)	(70)
Foreign currency translation adjustment	863	(229)	2,489	(1,847)
Defined benefit plans liability adjustments	4,165	3,847	12,496	11,654
Total other comprehensive income (loss)	22,166	(13,538)	46,721	137,068
Total comprehensive income	$ 378,089	$ 336,446	$ 1,132,624	$ 1,121,611

Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net income	$ 1,085,903	$ 984,543
Adjustments to reconcile net income to net cash provided by operating activities
Provision for credit losses	137,000	128,000
Depreciation and amortization of premises and equipment	84,631	79,911
Amortization of capitalized servicing rights	41,475	37,979
Amortization of core deposit and other intangible assets	24,341	33,524
Provision for deferred income taxes	9,926	109,274
Asset write-downs	10,878	14,276
Net gain on sales of assets	(27,967)	(46,732)
Net change in accrued interest receivable, payable	(23,059)	(13,833)
Net change in other accrued income and expense	110,138	113,809
Net change in loans originated for sale	523,895	(285,824)
Net change in trading account assets and liabilities	88,705	(82,837)
Net cash provided by operating activities	2,065,866	1,072,090
Cash flows from investing activities
Proceeds from sales of investment securities Available for sale	512,143	61,947
Proceeds from sales of investment securities Other	178,244	94,516
Proceeds from maturities of investment securities Available for sale	1,650,258	1,690,665
Proceeds from maturities of investment securities Held to maturity	390,278	459,399
Purchases of investment securities Available for sale	(248,705)	(1,150,523)
Purchases of investment securities Held to maturity	(1,175,608)	(15,806)
Purchases of investment securities Other	(132,104)	(1,514)
Net decrease (increase) in loans and leases	2,259,049	(2,021,004)
Net increase in interest-bearing deposits at banks	(1,305,846)	(3,183,286)
Capital expenditures, net	(62,515)	(65,277)
Net decrease in loan servicing advances	47,786	121,226
Other, net	66,357	11,459
Net cash provided (used) by investing activities	2,179,337	(3,998,198)
Cash flows from financing activities
Net increase (decrease) in deposits	(1,976,237)	6,195,511
Net increase (decrease) in short-term borrowings	37,326	(1,886,701)
Proceeds from long-term borrowings	2,145,950
Payments on long-term borrowings	(3,029,320)	(427,035)
Purchases of treasury stock	(981,691)	(604,000)
Dividends paid — common	(345,166)	(333,042)
Dividends paid — preferred	(53,842)	(58,003)
Other, net	5,480	3,540
Net cash provided (used) by financing activities	(4,197,500)	2,890,270
Net increase (decrease) in cash and cash equivalents	47,703	(35,838)
Cash and cash equivalents at beginning of period	1,320,549	1,368,040
Cash and cash equivalents at end of period	1,368,252	1,332,202
Supplemental disclosure of cash flow information
Interest received during the period	3,088,042	2,923,278
Interest paid during the period	310,640	387,695
Income taxes paid during the period	462,163	138,375
Supplemental schedule of noncash investing and financing activities
Real estate acquired in settlement of loans	88,551	100,106
Securitization of residential mortgage loans allocated to Available-for-sale investment securities	22,527	18,685
Securitization of residential mortgage loans allocated to capitalized servicing rights	$ 262	$ 193

Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2015	$ 16,173,289	$ 1,231,500	$ 79,782	$ 2,364	$ 6,680,768	$ 8,430,502	$ (251,627)
Total comprehensive income	1,121,611					984,543	137,068
Preferred stock cash dividends	(60,953)					(60,953)
Exercise of stock warrants into common stock					(223)			$ 223
Purchases of treasury stock	(604,000)							(604,000)
Stock-based compensation plans:
Compensation expense, net	18,376		171		7,315			10,890
Exercises of stock options, net	11,411		18		(183)			11,576
Stock purchase plan	10,594				275			10,319
Directors' stock plan	1,575		2		526			1,047
Deferred compensation plans, net, including dividend equivalents	28		2	(140)	232	(70)		4
Other	1,102				1,102
Common stock cash dividends	(332,057)					(332,057)
Ending balance at Sep. 30, 2016	16,340,976	1,231,500	79,975	2,224	6,689,812	9,021,965	(114,559)	(569,941)
Beginning balance at Dec. 31, 2016	16,486,622	1,231,500	79,973	2,145	6,676,948	9,222,488	(294,636)	(431,796)
Total comprehensive income	1,132,624					1,085,903	46,721
Preferred stock cash dividends	(54,604)					(54,604)
Exercise of stock warrants into common stock					(22,992)			22,992
Purchases of treasury stock	(981,691)							(981,691)
Stock-based compensation plans:
Compensation expense, net	6,016		(63)		(51,606)			57,685
Exercises of stock options, net	61,292				(6,722)			68,014
Stock purchase plan	10,831				2,563			8,268
Directors' stock plan	1,426				225			1,201
Deferred compensation plans, net, including dividend equivalents	(157)			(318)	(368)	(65)		594
Common stock cash dividends	(344,307)					(344,307)
Ending balance at Sep. 30, 2017	$ 16,318,052	$ 1,231,500	$ 79,910	$ 1,827	$ 6,598,048	$ 9,909,415	$ (247,915)	$ (1,254,733)

Consolidated Statement of Changes in Shareholders' Equity (Unaudited) (Parenthetical) - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Common stock per share dividend amount	$ 2.25	$ 2.10
Retained Earnings [Member]
Common stock per share dividend amount	$ 2.25	$ 2.10
Series A Warrants [Member] \| Common Stock [Member]
Exercise of warrants into shares of common stock	304,436	5,320
Exercise of warrants into shares of common stock	165,498	1,983

Significant accounting policies	9 Months Ended
Significant accounting policies	Sep. 30, 2017
Accounting Policies [Abstract]
Significant accounting policies	1. Significant accounting policies The consolidated financial statements of M&T Bank Corporation (“M&T”) and subsidiaries (“the Company”) were compiled in accordance with generally accepted accounting principles (“GAAP”) using the accounting policies set forth in note 1 of Notes to Financial Statements included in Form 10-K for the year ended December 31, 2016 (“2016 Annual Report”), except that effective January 2017 the Company adopted amended accounting guidance that is discussed in note 16 herein. The most significant of those changes related to the accounting for excess tax benefits or deficiencies associated with share-based compensation whereby beginning in 2017 those amounts are recognized in income tax expense. Previously, tax effects resulting from changes in M&T’s share price subsequent to the grant date were recorded through shareholders’ equity. The adoption of this new accounting guidance resulted in a reduction of income tax expense for the three months ended March 31, 2017 of $18 million, or $.12 of diluted earnings per common share. The impact on income tax expense and diluted earnings per common share in the second and third quarters of 2017 was not significant. In the opinion of management, all adjustments necessary for a fair statement have been made and were all of a normal recurring nature.

Acquisitions

9 Months Ended

Sep. 30, 2017

Business Combinations [Abstract]

Acquisitions

2. Acquisitions

In connection with the acquisition of Hudson City Bancorp, Inc. (“Hudson City”) on November 1, 2015 the Company incurred merger-related expenses related to systems conversions and other costs of integrating and conforming acquired operations with and into the Company. Those expenses consisted largely of professional services and other temporary help fees associated with systems conversions and/or integration of operations; costs related to termination of existing contractual arrangements for various services; initial marketing and promotion expenses designed to introduce the Company to its new customers; severance (for former Hudson City employees); travel costs; and other costs of completing the transaction and commencing operations in new markets and offices.

A summary of merger-related expenses included in the consolidated statement of income follows:

	Nine Months Ended September 30, 2016
	(In thousands)

Salaries and employee benefits	$	5,334
Equipment and net occupancy		1,278
Outside data processing and software		1,067
Advertising and marketing		10,522
Printing, postage and supplies		1,482
Other costs of operations		16,072
Total	$	35,755

There were no merger-related expenses during the three-month or nine-month periods ended September 30, 2017 or during the three-month period ended September 30, 2016.

Investment securities

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Investment securities

3. Investment securities

The amortized cost and estimated fair value of investment securities were as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In thousands)
September 30, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	2,017,901		25		10,809	$	2,007,117
Obligations of states and political subdivisions		2,621		59		2		2,678
Mortgage-backed securities:
Government issued or guaranteed		9,155,485		92,915		63,917		9,184,483
Privately issued		30		—		—		30
Other debt securities		136,769		2,739		10,978		128,530
Equity securities		57,009		37,427		450		93,986
		11,369,815		133,165		86,156		11,416,824
Investment securities held to maturity:
Obligations of states and political subdivisions		32,445		190		81		32,554
Mortgage-backed securities:
Government issued or guaranteed		3,063,164		41,849		7,147		3,097,866
Privately issued		141,430		1,753		30,734		112,449
Other debt securities		5,085		—		—		5,085
		3,242,124		43,792		37,962		3,247,954
Other securities		414,978		—		—		414,978
Total	$	15,026,917		176,957		124,118	$	15,079,756

December 31, 2016
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,912,110	386	9,952	$	1,902,544
Obligations of states and political subdivisions		3,570	77	6		3,641
Mortgage-backed securities:
Government issued or guaranteed		10,980,507	88,343	113,989		10,954,861
Privately issued		45	—	1		44
Other debt securities		134,105	1,407	16,996		118,516
Equity securities		307,964	45,073	571		352,466
		13,338,301	135,286	141,515		13,332,072
Investment securities held to maturity:
Obligations of states and political subdivisions		60,858	267	224		60,901
Mortgage-backed securities:
Government issued or guaranteed		2,233,173	37,498	7,374		2,263,297
Privately issued		157,704	897	37,120		121,481
Other debt securities		5,543	—	—		5,543
		2,457,278	38,662	44,718		2,451,222
Other securities		461,118	—	—		461,118
Total	$	16,256,697	173,948	186,233	$	16,244,412

3. Investment securities, continued

There were no significant gross realized gains or losses from sales of investment securities for the three-month and nine-month periods ended September 30, 2017. During the three months ended September 30, 2016, the Company sold substantially all of its collateralized debt obligations held in the available-for-sale investment securities portfolio for a gain of $28 million. There were no other significant gross realized gains or losses from the sale of investment securities for the three-month and nine-month periods ended September 30, 2016.

At September 30, 2017, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:

	Amortized Cost		Estimated Fair Value
	(In thousands)
Debt securities available for sale:
Due in one year or less	$	393,453		392,506
Due after one year through five years		1,632,143		1,622,447
Due after five years through ten years		72,508		72,854
Due after ten years		59,187		50,518
		2,157,291		2,138,325
Mortgage-backed securities available for sale		9,155,515		9,184,513
	$	11,312,806		11,322,838
Debt securities held to maturity:
Due in one year or less	$	18,640		18,738
Due after one year through five years		13,612		13,619
Due after five years through ten years		193		197
Due after ten years		5,085		5,085
		37,530		37,639
Mortgage-backed securities held to maturity		3,204,594		3,210,315
	$	3,242,124		3,247,954

3. Investment securities, continued

A summary of investment securities that as of September 30, 2017 and December 31, 2016 had been in a continuous unrealized loss position for less than twelve months and those that had been in a continuous unrealized loss position for twelve months or longer follows:

	Less Than 12 Months					12 Months or More
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(In thousands)
September 30, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,576,717		(8,002	)		373,852		(2,807	)
Obligations of states and political subdivisions		—		—			474		(2	)
Mortgage-backed securities:
Government issued or guaranteed		2,854,982		(32,123	)		1,298,054		(31,794	)
Other debt securities		1,500		(3	)		60,518		(10,975	)
Equity securities		18,185		(303	)		153		(147	)
		4,451,384		(40,431	)		1,733,051		(45,725	)

Investment securities held to maturity:
Obligations of states and political subdivisions		4,932		(31	)		7,093		(50	)
Mortgage-backed securities:
Government issued or guaranteed		638,863		(2,832	)		157,923		(4,315	)
Privately issued		—		—			53,631		(30,734	)
		643,795		(2,863	)		218,647		(35,099	)
Total	$	5,095,179		(43,294	)		1,951,698		(80,824	)

December 31, 2016
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,710,241		(9,950	)		2,295		(2	)
Obligations of states and political subdivisions		—		—			593		(6	)
Mortgage-backed securities:
Government issued or guaranteed		6,730,829		(113,374	)		81,003		(615	)
Privately issued		—		—			27		(1	)
Other debt securities		100		(1	)		85,400		(16,995	)
Equity securities		17,776		(422	)		151		(149	)
		8,458,946		(123,747	)		169,469		(17,768	)

Investment securities held to maturity:
Obligations of states and political subdivisions		17,988		(126	)		11,891		(98	)
Mortgage-backed securities:
Government issued or guaranteed		618,832		(6,842	)		17,481		(532	)
Privately issued		17,911		(1,222	)		57,016		(35,898	)
		654,731		(8,190	)		86,388		(36,528	)
Total	$	9,113,677		(131,937	)		255,857		(54,296	)

The Company owned 939 individual investment securities with aggregate gross unrealized losses of $124 million at September 30, 2017. Based on a review of each of the securities in the investment securities portfolio at September 30, 2017, the Company concluded that it expected to recover the amortized cost basis of its investment. As of September 30, 2017, the Company does not intend to sell nor is it anticipated that it would be required to sell any of its impaired investment securities at a loss. At September 30, 2017, the Company has not identified

3. Investment securities, continued

events or changes in circumstances which may have a significant adverse effect on the carrying value of the $415 million of cost method investment securities.

Loans and leases and the allowance for credit losses

9 Months Ended

Sep. 30, 2017

Receivables [Abstract]

Loans and leases and the allowance for credit losses

4. Loans and leases and the allowance for credit losses

A summary of current, past due and nonaccrual loans as of September 30, 2017 and December 31, 2016 follows:

	Current		30-89 Days Past Due		Accruing Loans Past Due 90 Days or More (a)		Accruing Loans Acquired at a Discount Past Due 90 days or More (b)		Purchased Impaired (c)		Nonaccrual		Total
	(In thousands)
September 30, 2017
Commercial, financial, leasing, etc.	$	21,486,942		48,159		3,710		369		75		203,996	$	21,743,251
Real estate:
Commercial		24,724,768		273,539		1,710		7,523		20,509		200,193		25,228,242
Residential builder and developer		1,604,095		26,182		—		4,413		10,717		2,416		1,647,823
Other commercial construction		5,952,636		51,132		1,220		—		13,972		19,263		6,038,223
Residential		15,868,656		458,066		249,983		10,025		307,529		236,363		17,130,622
Residential — limited documentation		2,829,667		88,814		—		—		114,141		101,918		3,134,540
Consumer:
Home equity lines and loans		5,275,572		34,878		772		9,856		—		75,584		5,396,662
Automobile		3,327,148		67,280		—		1		—		21,267		3,415,696
Other		4,120,712		33,070		3,893		24,038		—		8,362		4,190,075
Total	$	85,190,196		1,081,120		261,288		56,225		466,943		869,362	$	87,925,134

December 31, 2016
Commercial, financial, leasing, etc.	$	22,287,857		53,503		6,195		417		641		261,434	$	22,610,047
Real estate:
Commercial		25,076,684		183,531		7,054		12,870		31,404		176,201		25,487,744
Residential builder and developer		1,884,989		4,667		5		1,952		14,006		16,707		1,922,326
Other commercial construction		5,985,118		77,701		922		198		14,274		18,111		6,096,324
Residential		17,631,377		485,468		281,298		11,537		378,549		229,242		19,017,471
Residential — limited documentation		3,239,344		88,366		—		—		139,158		106,573		3,573,441
Consumer:
Home equity lines and loans		5,502,091		44,565		—		12,678		—		81,815		5,641,149
Automobile		2,869,232		56,158		—		1		—		18,674		2,944,065
Other		3,491,629		31,286		5,185		21,491		—		11,258		3,560,849
Total	$	87,968,321		1,025,245		300,659		61,144		578,032		920,015	$	90,853,416

(a)	Excludes loans acquired at a discount.

(b)	Loans acquired at a discount that were recorded at fair value at acquisition date. This category does not include purchased impaired loans that are presented separately.

(c)	Accruing loans acquired at a discount that were impaired at acquisition date and recorded at fair value.

4. Loans and leases and the allowance for credit losses, continued

One-to-four family residential mortgage loans held for sale were $347 million and $414 million at September 30, 2017 and December 31, 2016, respectively. Commercial real estate loans held for sale were $224 million at September 30, 2017 and $643 million at December 31, 2016.

The outstanding principal balance and the carrying amount of loans acquired at a discount that were recorded at fair value at the acquisition date and included in the consolidated balance sheet were as follows:

	September 30,		December 31,
	2017		2016
	(In thousands)

Outstanding principal balance	$	1,584,126		2,311,699
Carrying amount:
Commercial, financial, leasing, etc.		42,878		59,928
Commercial real estate		308,426		456,820
Residential real estate		665,278		799,802
Consumer		127,919		487,721
	$	1,144,501		1,804,271

Purchased impaired loans included in the table above totaled $467 million at September 30, 2017 and $578 million at December 31, 2016, representing less than 1% of the Company’s assets as of each date. A summary of changes in the accretable yield for loans acquired at a discount for the three months and nine months ended September 30, 2017 and 2016 follows:


	Three Months Ended September 30
	2017						2016
	Purchased			Other			Purchased			Other
	Impaired			Acquired			Impaired			Acquired
	(In thousands)

Balance at beginning of period	$	133,532			163,099		$	162,023			245,195
Interest income		(10,815	)		(20,064	)		(12,784	)		(26,540	)
Reclassifications from nonaccretable balance		30,799			6,041			2,256			12,050
Other (a)		—			1,545			—			(818	)
Balance at end of period	$	153,516			150,621		$	151,495			229,887

	Nine Months Ended September 30
	2017						2016
	Purchased			Other			Purchased			Other
	Impaired			Acquired			Impaired			Acquired
	(In thousands)

Balance at beginning of period	$	154,233			201,153		$	184,618			296,434
Interest income		(32,546	)		(66,505	)		(40,906	)		(97,300	)
Reclassifications from nonaccretable balance		31,829			11,076			7,783			20,647
Other (a)		—			4,897			—			10,106
Balance at end of period	$	153,516			150,621		$	151,495			229,887

(a)	Other changes in expected cash flows including changes in interest rates and prepayment assumptions.

4. Loans and leases and the allowance for credit losses, continued

Changes in the allowance for credit losses for the three months ended September 30, 2017 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	339,314			366,229			66,006			158,559			78,117	$	1,008,225
Provision for credit losses		2,451			(7,699	)		1,267			33,886			95		30,000
Net charge-offs
Charge-offs		(9,714	)		(258	)		(4,206	)		(32,874	)		—		(47,052	)
Recoveries		4,423			5,895			2,028			9,807			—		22,153
Net (charge-offs) recoveries		(5,291	)		5,637			(2,178	)		(23,067	)		—		(24,899	)
Ending balance	$	336,474			364,167			65,095			169,378			78,212	$	1,013,326

Changes in the allowance for credit losses for the three months ended September 30, 2016 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	316,079			349,674			69,660			157,361			77,722	$	970,496
Provision for credit losses		26,222			9,963			(6,232	)		16,539			508		47,000
Net charge-offs
Charge-offs		(21,075	)		(1,564	)		(6,754	)		(29,882	)		—		(59,275	)
Recoveries		6,958			1,704			1,919			7,319			—		17,900
Net (charge-offs) recoveries		(14,117	)		140			(4,835	)		(22,563	)		—		(41,375	)
Ending balance	$	328,184			359,777			58,593			151,337			78,230	$	976,121

Changes in the allowance for credit losses for the nine months ended September 30, 2017 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	330,833			362,719			61,127			156,288			78,030	$	988,997
Provision for credit losses		44,642			1,201			14,067			76,908			182		137,000
Net charge-offs
Charge-offs		(51,318	)		(7,556	)		(16,364	)		(96,060	)		—		(171,298	)
Recoveries		12,317			7,803			6,265			32,242			—		58,627
Net (charge-offs) recoveries		(39,001	)		247			(10,099	)		(63,818	)		—		(112,671	)
Ending balance	$	336,474			364,167			65,095			169,378			78,212	$	1,013,326

4. Loans and leases and the allowance for credit losses, continued

Changes in the allowance for credit losses for the nine months ended September 30, 2016 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	300,404			326,831			72,238			178,320			78,199	$	955,992
Provision for credit losses		39,667			29,799			(610	)		59,113			31		128,000
Net charge-offs
Charge-offs		(34,711	)		(3,569	)		(18,816	)		(107,761	)		—		(164,857	)
Recoveries		22,824			6,716			5,781			21,665			—		56,986
Net (charge-offs) recoveries		(11,887	)		3,147			(13,035	)		(86,096	)		—		(107,871	)
Ending balance	$	328,184			359,777			58,593			151,337			78,230	$	976,121

Despite the allocation in the preceding tables, the allowance for credit losses is general in nature and is available to absorb losses from any loan or lease type.

In establishing the allowance for credit losses, the Company estimates losses attributable to specific troubled credits identified through both normal and detailed or intensified credit review processes and also estimates losses inherent in other loans and leases on a collective basis. For purposes of determining the level of the allowance for credit losses, the Company evaluates its loan and lease portfolio by loan type. The amounts of loss components in the Company’s loan and lease portfolios are determined through a loan-by-loan analysis of larger balance commercial loans and commercial real estate loans that are in nonaccrual status and by applying loss factors to groups of loan balances based on loan type and management’s classification of such loans under the Company’s loan grading system. Measurement of the specific loss components is typically based on expected future cash flows, collateral values and other factors that may impact the borrower’s ability to pay. In determining the allowance for credit losses, the Company utilizes a loan grading system which is applied to commercial and commercial real estate credits on an individual loan basis. Loan officers are responsible for continually assigning grades to these loans based on standards outlined in the Company’s Credit Policy. Internal loan grades are also monitored by the Company’s credit review department to ensure consistency and strict adherence to the prescribed standards. Loan grades are assigned loss component factors that reflect the Company’s loss estimate for each group of loans and leases. Factors considered in assigning loan grades and loss component factors include borrower-specific information related to expected future cash flows and operating results, collateral values, geographic location, financial condition and performance, payment status, and other information; levels of and trends in portfolio charge-offs and recoveries; levels of and trends in portfolio delinquencies and impaired loans; changes in the risk profile of specific portfolios; trends in volume and terms of loans; effects of changes in credit concentrations; and observed trends and practices in the banking industry. As updated appraisals are obtained on individual loans or other events in the market place indicate that collateral values have significantly changed, individual loan grades are adjusted as appropriate. Changes in other factors cited may also lead to loan grade changes at any time. Except for consumer loans and residential real estate loans that are considered smaller balance homogenous loans and acquired loans that are evaluated on an aggregated basis, the Company considers a loan to be impaired for purposes of applying GAAP when, based on current information and events, it is probable that the Company will be unable to collect all amounts according to the contractual terms of the loan agreement or the loan is delinquent 90 days. Regardless of loan type, the Company considers a loan to be impaired if it qualifies as a troubled debt restructuring. Modified loans, including smaller balance homogenous loans, that are considered to be troubled debt restructurings are evaluated for impairment giving consideration to the impact of the modified loan terms on the present value of the loan’s expected cash flows.

4. Loans and leases and the allowance for credit losses, continued

The following tables provide information with respect to loans and leases that were considered impaired as of September 30, 2017 and December 31, 2016 and for the three-month and nine-month periods ended September 30, 2017 and 2016.

	September 30, 2017						December 31, 2016
	Recorded Investment		Unpaid Principal Balance		Related Allowance		Recorded Investment		Unpaid Principal Balance		Related Allowance
	(In thousands)
With an allowance recorded:
Commercial, financial, leasing, etc.	$	148,747		179,120		49,447		168,072		184,432		48,480
Real estate:
Commercial		73,144		81,244		10,200		71,862		86,666		11,620
Residential builder and developer		6,537		6,842		288		7,396		8,361		506
Other commercial construction		1,626		1,785		292		2,475		2,731		448
Residential		97,483		118,030		3,475		86,680		105,944		3,457
Residential — limited documentation		79,030		94,194		4,600		82,547		97,718		6,000
Consumer:
Home equity lines and loans		48,231		52,975		8,711		44,693		48,965		8,027
Automobile		14,225		16,743		3,011		16,982		18,272		3,740
Other		3,176		5,633		650		3,791		5,296		776
		472,199		556,566		80,674		484,498		558,385		83,054
With no related allowance recorded:
Commercial, financial, leasing, etc.		80,952		97,073		—		100,805		124,786		—
Real estate:
Commercial		148,733		158,815		—		113,276		121,846		—
Residential builder and developer		1,174		1,174		—		14,368		21,124		—
Other commercial construction		17,850		37,237		—		15,933		35,281		—
Residential		17,312		23,291		—		16,823		24,161		—
Residential — limited documentation		11,091		18,480		—		15,429		24,590		—
		277,112		336,070		—		276,634		351,788		—
Total:
Commercial, financial, leasing, etc.		229,699		276,193		49,447		268,877		309,218		48,480
Real estate:
Commercial		221,877		240,059		10,200		185,138		208,512		11,620
Residential builder and developer		7,711		8,016		288		21,764		29,485		506
Other commercial construction		19,476		39,022		292		18,408		38,012		448
Residential		114,795		141,321		3,475		103,503		130,105		3,457
Residential — limited documentation		90,121		112,674		4,600		97,976		122,308		6,000
Consumer:
Home equity lines and loans		48,231		52,975		8,711		44,693		48,965		8,027
Automobile		14,225		16,743		3,011		16,982		18,272		3,740
Other		3,176		5,633		650		3,791		5,296		776
Total	$	749,311		892,636		80,674		761,132		910,173		83,054

4. Loans and leases and the allowance for credit losses, continued

	Three Months Ended September 30, 2017						Three Months Ended September 30, 2016
			Interest Income Recognized						Interest Income Recognized
	Average Recorded Investment		Total		Cash Basis		Average Recorded Investment		Total		Cash Basis
	(In thousands)

Commercial, financial, leasing, etc.	$	224,526		391		391		262,796		744		744
Real estate:
Commercial		233,572		1,425		1,425		175,256		1,806		1,806
Residential builder and developer		8,550		895		895		26,996		405		405
Other commercial construction		16,578		25		25		21,500		190		190
Residential		113,892		1,903		905		96,961		1,572		570
Residential — limited documentation		91,974		1,624		569		101,877		1,501		378
Consumer:
Home equity lines and loans		47,831		419		99		41,740		368		112
Automobile		14,588		251		22		18,571		303		19
Other		3,269		80		2		4,077		72		11
Total	$	754,780		7,013		4,333		749,774		6,961		4,235

	Nine Months Ended September 30, 2017						Nine Months Ended September 30, 2016
			Interest Income Recognized						Interest Income Recognized
	Average Recorded Investment		Total		Cash Basis		Average Recorded Investment		Total		Cash Basis
	(In thousands)

Commercial, financial, leasing, etc.	$	242,410		1,674		1,674		283,783		7,055		7,055
Real estate:
Commercial		205,814		3,213		3,213		177,579		3,891		3,891
Residential builder and developer		14,551		1,791		1,791		30,832		488		488
Other commercial construction		15,474		958		958		19,774		563		563
Residential		108,741		5,004		2,285		97,229		4,778		2,591
Residential — limited documentation		94,680		4,573		1,292		104,382		4,580		1,648
Consumer:
Home equity lines and loans		46,829		1,240		290		33,998		937		295
Automobile		15,483		788		62		20,358		964		83
Other		3,430		227		8		10,987		371		74
Total	$	747,412		19,468		11,573		778,922		23,627		16,688

4. Loans and leases and the allowance for credit losses, continued

In accordance with the previously described policies, the Company utilizes a loan grading system that is applied to all commercial loans and commercial real estate loans. Loan grades are utilized to differentiate risk within the portfolio and consider the expectations of default for each loan. Commercial loans and commercial real estate loans with a lower expectation of default are assigned one of ten possible “pass” loan grades and are generally ascribed lower loss factors when determining the allowance for credit losses. Loans with an elevated level of credit risk are classified as “criticized” and are ascribed a higher loss factor when determining the allowance for credit losses. Criticized loans may be classified as “nonaccrual” if the Company no longer expects to collect all amounts according to the contractual terms of the loan agreement or the loan is delinquent 90 days or more. All larger- balance criticized commercial loans and commercial real estate loans are individually reviewed by centralized credit personnel each quarter to determine the appropriateness of the assigned loan grade, including whether the loan should be reported as accruing or nonaccruing. Smaller-balance criticized loans are analyzed by business line risk management areas to ensure proper loan grade classification. Furthermore, criticized nonaccrual commercial loans and commercial real estate loans are considered impaired and, as a result, specific loss allowances on such loans are established within the allowance for credit losses to the extent appropriate in each individual instance.

The following table summarizes the loan grades applied to the various classes of the Company’s commercial loans and commercial real estate loans.

			Real Estate
	Commercial,				Residential		Other
	Financial,				Builder and		Commercial
	Leasing, etc.		Commercial		Developer		Construction
	(In thousands)
September 30, 2017
Pass	$	20,561,077		24,309,923		1,580,763		5,830,122
Criticized accrual		978,178		718,126		64,644		188,838
Criticized nonaccrual		203,996		200,193		2,416		19,263
Total	$	21,743,251		25,228,242		1,647,823		6,038,223
December 31, 2016
Pass	$	21,398,581		24,570,269		1,789,071		5,912,351
Criticized accrual		950,032		741,274		116,548		165,862
Criticized nonaccrual		261,434		176,201		16,707		18,111
Total	$	22,610,047		25,487,744		1,922,326		6,096,324

4. Loans and leases and the allowance for credit losses, continued

In determining the allowance for credit losses, residential real estate loans and consumer loans are generally evaluated collectively after considering such factors as payment performance and recent loss experience and trends, which are mainly driven by current collateral values in the market place as well as the amount of loan defaults. Loss rates on such loans are determined by reference to recent charge-off history and are evaluated (and adjusted if deemed appropriate) through consideration of other factors including near-term forecasted loss estimates developed by the Company’s credit department. In arriving at such forecasts, the Company considers the current estimated fair value of its collateral based on geographical adjustments for home price depreciation/appreciation and overall borrower repayment performance. With regard to collateral values, the realizability of such values by the Company contemplates repayment of any first lien position prior to recovering amounts on a second lien position. However, residential real estate loans and outstanding balances of home equity loans and lines of credit that are more than 150 days past due are generally evaluated for collectability on a loan-by-loan basis giving consideration to estimated collateral values. The carrying value of residential real estate loans and home equity loans and lines of credit for which a partial charge-off has been recognized totaled $39 million and $27 million, respectively, at September 30, 2017 and $44 million and $32 million, respectively, at December 31, 2016. Residential real estate loans and home equity loans and lines of credit that were more than 150 days past due but did not require a partial charge-off because the net realizable value of the collateral exceeded the outstanding customer balance were $19 million and $33 million, respectively, at September 30, 2017 and $16 million and $39 million, respectively, at December 31, 2016.

The Company also measures additional losses for purchased impaired loans when it is probable that the Company will be unable to collect all cash flows expected at acquisition plus additional cash flows expected to be collected arising from changes in estimates after acquisition. The determination of the allocated portion of the allowance for credit losses is very subjective. Given that inherent subjectivity and potential imprecision involved in determining the allocated portion of the allowance for credit losses, the Company also provides an inherent unallocated portion of the allowance. The unallocated portion of the allowance is intended to recognize probable losses that are not otherwise identifiable and includes management’s subjective determination of amounts necessary to provide for the possible use of imprecise estimates in determining the allocated portion of the allowance. Therefore, the level of the unallocated portion of the allowance is primarily reflective of the inherent imprecision in the various calculations used in determining the allocated portion of the allowance for credit losses. Other factors that could also lead to changes in the unallocated portion include the effects of expansion into new markets for which the Company does not have the same degree of familiarity and experience regarding portfolio performance in changing market conditions, the introduction of new loan and lease product types, and other risks associated with the Company’s loan portfolio that may not be specifically identifiable.

4. Loans and leases and the allowance for credit losses, continued

The allocation of the allowance for credit losses summarized on the basis of the Company’s impairment methodology was as follows:

	Commercial, Financial,		Real Estate
	Leasing, etc.		Commercial		Residential		Consumer		Total
	(In thousands)
September 30, 2017
Individually evaluated for impairment	$	49,447		10,780		8,075		12,372	$	80,674
Collectively evaluated for impairment		287,027		353,387		47,674		157,006		845,094
Purchased impaired		—		—		9,346		—		9,346
Allocated	$	336,474		364,167		65,095		169,378		935,114
Unallocated										78,212
Total									$	1,013,326
December 31, 2016
Individually evaluated for impairment	$	48,480		12,500		9,457		12,543	$	82,980
Collectively evaluated for impairment		282,353		348,301		47,993		143,745		822,392
Purchased impaired		—		1,918		3,677		—		5,595
Allocated	$	330,833		362,719		61,127		156,288		910,967
Unallocated										78,030
Total									$	988,997

The recorded investment in loans and leases summarized on the basis of the Company’s impairment methodology was as follows:

	Commercial, Financial,		Real Estate
	Leasing, etc.		Commercial		Residential		Consumer		Total
	(In thousands)
September 30, 2017
Individually evaluated for impairment	$	229,699		249,064		204,916		65,632	$	749,311
Collectively evaluated for impairment		21,513,477		32,620,026		19,638,576		12,936,801		86,708,880
Purchased impaired		75		45,198		421,670		—		466,943
Total	$	21,743,251		32,914,288		20,265,162		13,002,433	$	87,925,134
December 31, 2016
Individually evaluated for impairment	$	268,877		224,630		201,479		65,466	$	760,452
Collectively evaluated for impairment		22,340,529		33,222,080		21,871,726		12,080,597		89,514,932
Purchased impaired		641		59,684		517,707		—		578,032
Total	$	22,610,047		33,506,394		22,590,912		12,146,063	$	90,853,416

During the normal course of business, the Company modifies loans to maximize recovery efforts. If the borrower is experiencing financial difficulty and a concession is granted, the Company considers such modifications as troubled debt restructurings and classifies those loans as either nonaccrual loans or renegotiated loans. The types of concessions that the Company grants typically include principal deferrals and interest rate concessions, but may also include other types of concessions.

4. Loans and leases and the allowance for credit losses, continued

The tables that follow summarize the Company’s loan modification activities that were considered troubled debt restructurings for the three-month and nine-month periods ended September 30, 2017 and 2016:

					Post-modification (a)
	Number		Pre- modification recorded investment		Principal Deferral		Other		Combination of Concession Types		Total
Three Months Ended September 30, 2017	(Dollars in thousands)

Commercial, financial, leasing, etc.		49	$	15,812	$	5,888	$	97	$	9,251	$	15,236
Real estate:
Commercial		17		5,861		1,420		868		3,450		5,738
Residential		34		5,123		3,033		—		2,716		5,749
Residential — limited documentation		4		515		383		—		167		550
Consumer:
Home equity lines and loans		25		2,154		461		—		1,776		2,237
Automobile		17		342		326		—		16		342
Other		1		5		5		—		—		5
Total		147	$	29,812	$	11,516	$	965	$	17,376	$	29,857

Three Months Ended September 30, 2016

Commercial, financial, leasing, etc.		43	$	69,486	$	40,183	$	—	$	19,802	$	59,985
Real estate:
Commercial		18		14,925		11,644		—		2,614		14,258
Residential		30		5,638		4,714		—		1,214		5,928
Residential — limited documentation		6		827		470		—		493		963
Consumer:
Home equity lines and loans		26		2,552		251		—		2,301		2,552
Automobile		10		186		186		—		—		186
Other		1		26		26		—		—		26
Total		134	$	93,640	$	57,474	$	—	$	26,424	$	83,898

4. Loans and leases and the allowance for credit losses, continued

					Post-modification (a)
	Number		Pre- modification recorded investment		Principal Deferral		Other		Combination of Concession Types		Total
Nine Months Ended September 30, 2017	(Dollars in thousands)

Commercial, financial, leasing, etc.		162	$	93,346	$	18,449	$	6,459	$	47,211	$	72,119
Real estate:
Commercial		67		38,608		16,193		868		21,332		38,393
Residential builder and developer		3		12,291		—		—		10,879		10,879
Other commercial construction		2		168		168		—		—		168
Residential		105		22,459		11,608		—		12,557		24,165
Residential — limited documentation		17		3,724		618		—		3,352		3,970
Consumer:
Home equity lines and loans		85		7,885		1,040		491		6,442		7,973
Automobile		59		1,160		1,089		—		71		1,160
Other		6		85		85		—		—		85
Total		506	$	179,726	$	49,250	$	7,818	$	101,844	$	158,912

Nine Months Ended September 30, 2016

Commercial, financial, leasing, etc.		112	$	148,204	$	98,561	$	—	$	39,971	$	138,532
Real estate:
Commercial		55		36,984		17,802		4,576		13,546		35,924
Residential builder and developer		3		23,905		22,958		—		—		22,958
Other commercial construction		2		374		250		—		124		374
Residential		73		11,946		7,945		—		4,705		12,650
Residential — limited documentation		14		2,415		803		—		1,872		2,675
Consumer:
Home equity lines and loans		84		9,189		655		—		8,534		9,189
Automobile		148		1,005		865		55		85		1,005
Other		78		1,192		951		45		196		1,192
Total		569	$	235,214	$	150,790	$	4,676	$	69,033	$	224,499

(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages. The present value of interest rate concessions, discounted at the effective rate of the original loan, was not material.

Troubled debt restructurings are considered to be impaired loans and for purposes of establishing the allowance for credit losses are evaluated for impairment giving consideration to the impact of the modified loan terms on the present value of the loan’s expected cash flows. Impairment of troubled debt restructurings that have subsequently defaulted may also be measured based on the loan’s observable market price or the fair value of collateral if the loan is collateral-dependent. Charge-offs may also be recognized on troubled debt restructurings that have subsequently defaulted. Loans that were modified as troubled debt restructurings during the twelve months ended September 30, 2017 and 2016 and for which there was a subsequent payment default during the nine-month periods ended September 30, 2017 and 2016, respectively, were not material.

4. Loans and leases and the allowance for credit losses, continued

The amount of foreclosed residential real estate property held by the Company totaled $106 million and $129 million at September 30, 2017 and December 31, 2016, respectively. There were $545 million and $506 million at September 30, 2017 and December 31, 2016, respectively, in loans secured by residential real estate that were in the process of foreclosure. Of all loans in the process of foreclosure at September 30, 2017, approximately 48% were classified as purchased impaired and 20% were government guaranteed.

- Definition

The entire disclosure for claims held for amounts due a entity, excluding financing receivables. Examples include, but are not limited to, trade accounts receivables, notes receivables, loans receivables. Includes disclosure for allowance for credit losses.

+ References + Details

Borrowings	9 Months Ended
Borrowings	Sep. 30, 2017
Debt Disclosure [Abstract]
Borrowings	5. Borrowings During May 2017, M&T Bank, the principal bank subsidiary of M&T, issued $900 million of senior notes that mature in May 2022 pursuant to a Bank Note Program, of which $650 million have a 2.50% fixed interest rate and $250 million have a variable rate paid quarterly at rates that are indexed to the three-month London Interbank Offered Rate (“LIBOR”). During June 2017, M&T Bank redeemed $750 million of 1.40% fixed rate senior notes. The notes had a maturity date of July 25, 2017 and were redeemable on or after the 30^th day prior to the maturity date. During August 2017, M&T Bank issued $750 million of three-year 2.05% fixed rate senior notes due August 2020 and $500 million of ten-year 3.40% fixed rate subordinated notes due August 2027. M&T had $519 million of fixed and variable rate junior subordinated deferrable interest debentures ("Junior Subordinated Debentures") outstanding at September 30, 2017 that are held by various trusts that were issued in connection with the issuance by those trusts of preferred capital securities ("Capital Securities") and common securities ("Common Securities"). The proceeds from the issuances of the Capital Securities and the Common Securities were used by the trusts to purchase the Junior Subordinated Debentures. The Common Securities of each of those trusts are wholly owned by M&T and are the only class of each trust's securities possessing general voting powers. The Capital Securities represent preferred undivided interests in the assets of the corresponding trust. Under the Federal Reserve Board’s risk-based capital guidelines, the securities are includable in M&T’s Tier 2 regulatory capital. Holders of the Capital Securities receive preferential cumulative cash distributions unless M&T exercises its right to extend the payment of interest on the Junior Subordinated Debentures as allowed by the terms of each such debenture, in which case payment of distributions on the respective Capital Securities will be deferred for comparable periods. During an extended interest period, M&T may not pay dividends or distributions on, or repurchase, redeem or acquire any shares of its capital stock. In general, the agreements governing the Capital Securities, in the aggregate, provide a full, irrevocable and unconditional guarantee by M&T of the payment of distributions on, the redemption of, and any liquidation distribution with respect to the Capital Securities. The obligations under such guarantee and the Capital Securities are subordinate and junior in right of payment to all senior indebtedness of M&T. The Capital Securities will remain outstanding until the Junior Subordinated Debentures are repaid at maturity, are redeemed prior to maturity or are distributed in liquidation to the trusts. The Capital Securities are mandatorily redeemable in whole, but not in part, upon repayment at the stated maturity dates (ranging from 2027 to 2033) of the Junior Subordinated Debentures or the earlier redemption of the Junior Subordinated Debentures in whole upon the occurrence of one or more events set forth in the indentures relating to the Capital Securities, and in whole or in part at any time after an optional redemption prior to contractual maturity contemporaneously with the optional redemption of the related Junior Subordinated Debentures in whole or in part, subject to possible regulatory approval. 5. Borrowings, continued Also included in long-term borrowings are agreements to repurchase securities of $425 million and $1.1 billion at September 30, 2017 and December 31, 2016, respectively. The agreements reflect various repurchase dates through 2020, however, the contractual maturities of the underlying investment securities extend beyond such repurchase dates. The agreements are subject to legally enforceable master netting arrangements, however, the Company has not offset any amounts related to these agreements in its consolidated financial statements. The Company posted collateral consisting primarily of government guaranteed mortgage-backed securities of $445 million and $1.1 billion at September 30, 2017 and December 31, 2016, respectively.

Shareholders' equity

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Shareholders' equity

6. Shareholders' equity

M&T is authorized to issue 1,000,000 shares of preferred stock with a $1.00 par value per share. Preferred shares outstanding rank senior to common shares both as to dividends and liquidation preference, but have no general voting rights.

Issued and outstanding preferred stock of M&T as of September 30, 2017 and December 31, 2016 is presented below:

	Shares Issued and Outstanding		Carrying Value
	(Dollars in thousands)
Series A (a)
Fixed Rate Cumulative Perpetual Preferred Stock, $1,000 liquidation preference per share		230,000	$	230,000
Series C (a)
Fixed Rate Cumulative Perpetual Preferred Stock, $1,000 liquidation preference per share		151,500	$	151,500
Series E (b)
Fixed-to-Floating Rate Non-cumulative Perpetual Preferred Stock, $1,000 liquidation preference per share		350,000	$	350,000
Series F (c)
Fixed-to-Floating Rate Non-cumulative Perpetual Preferred Stock, $10,000 liquidation preference per share		50,000	$	500,000

(a)	Dividends, if declared, are paid at 6.375%. Warrants to purchase M&T common stock at $73.79 per share issued in connection with the Series A preferred stock expire in 2018 and totaled 327,358 at September 30, 2017.

(b)

Dividends, if declared, are paid semi-annually at a rate of 6.45% through February 14, 2024 and thereafter will be paid quarterly at a rate of the three-month LIBOR plus 361 basis points (hundredths of one percent). The shares are redeemable in whole or in part on or after February 15, 2024. Notwithstanding M&T’s option to redeem the shares, if an event occurs such that the shares no longer qualify as Tier 1 capital, M&T may redeem all of the shares within 90 days following that occurrence.

(c)

Dividends, if declared, are paid semi-annually at a rate of 5.125% through October 31, 2026 and thereafter will be paid quarterly at a rate of the three-month LIBOR plus 352 basis points. The shares are redeemable in whole or in part on or after November 1, 2026. Notwithstanding M&T’s option to redeem the shares, if an event occurs such that the shares no longer qualify as Tier 1 capital, M&T may redeem all of the shares within 90 days following that occurrence.

In addition to the Series A warrants mentioned in (a) above, a warrant to purchase 95,472 shares of M&T common stock at $518.47 per share was outstanding at September 30, 2017. The obligation under that warrant was assumed by M&T in an acquisition and expires in 2018.

Pension plans and other postretirement benefits

9 Months Ended

Sep. 30, 2017

Compensation And Retirement Disclosure [Abstract]

Pension plans and other postretirement benefits

7. Pension plans and other postretirement benefits

The Company provides defined benefit pension and other postretirement benefits (including health care and life insurance benefits) to qualified retired employees. Net periodic defined benefit cost for defined benefit plans consisted of the following:

	Pension Benefits						Other Postretirement Benefits
	Three Months Ended September 30
	2017			2016			2017			2016
	(In thousands)

Service cost	$	5,048			6,259			293		399
Interest cost on projected benefit obligation		19,818			20,853			929			1,242
Expected return on plan assets		(27,131	)		(27,118	)		—			—
Amortization of prior service cost (credit)		139			(807	)		(340	)		(339	)
Amortization of net actuarial loss (gain)		7,316			7,536			(247	)		15
Net periodic benefit cost	$	5,190			6,723			635			1,317

	Pension Benefits						Other Postretirement Benefits
	Nine Months Ended September 30
	2017			2016			2017			2016
	(In thousands)

Service cost	$	15,145			18,778			878			1,197
Interest cost on projected benefit obligation		59,452			62,558			2,787			3,728
Expected return on plan assets		(81,393	)		(81,355	)		—			—
Amortization of prior service cost (credit)		418			(2,421	)		(1,019	)		(1,019	)
Amortization of net actuarial loss (gain)		21,947			22,609			(741	)		45
Net periodic benefit cost	$	15,569			20,169			1,905			3,951

Expense incurred in connection with the Company's defined contribution pension and retirement savings plans totaled $16,085,000 and $14,783,000 for the three months ended September 30, 2017 and 2016, respectively, and $53,127,000 and $47,747,000 for the nine months ended September 30, 2017 and 2016, respectively.

Earnings per common share

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Earnings per common share

8. Earnings per common share

The computations of basic earnings per common share follow:

	Three Months Ended September 30						Nine Months Ended September 30
	2017			2016			2017			2016
	(In thousands, except per share)
Income available to common shareholders:
Net income	$	355,923			349,984			1,085,903			984,543
Less: Preferred stock dividends (a)		(18,130	)		(20,318	)		(54,604	)		(60,953	)
Net income available to common equity		337,793			329,666			1,031,299			923,590
Less: Income attributable to unvested stock-based compensation awards		(1,992	)		(2,674	)		(6,288	)		(7,920	)
Net income available to common shareholders	$	335,801			326,992			1,025,011			915,670
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards		152,245			156,767			153,814			158,710
Less: Unvested stock-based compensation awards		(898	)		(1,274	)		(948	)		(1,374	)
Weighted-average shares outstanding		151,347			155,493			152,866			157,336

Basic earnings per common share	$	2.22			2.10			6.71			5.82

(a)Including impact of not as yet declared cumulative dividends.

The computations of diluted earnings per common share follow:

	Three Months Ended September 30						Nine Months Ended September 30
	2017			2016			2017			2016
	(In thousands, except per share)

Net income available to common equity	$	337,793			329,666			1,031,299			923,590
Less: Income attributable to unvested stock-based compensation awards		(1,989	)		(2,668	)		(6,276	)		(7,904	)
Net income available to common shareholders	$	335,804			326,998			1,025,023			915,686
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards		152,245			156,767			153,814			158,710
Less: Unvested stock-based compensation awards		(898	)		(1,274	)		(948	)		(1,374	)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock		344			533			427			507
Adjusted weighted-average shares outstanding		151,691			156,026			153,293			157,843

Diluted earnings per common share	$	2.21			2.10			6.69			5.80

GAAP defines unvested share-based awards that contain nonforfeitable rights to dividends or dividend equivalents (whether paid or unpaid) as participating securities that shall be included in the computation of earnings per common share pursuant to the two-class method. The Company has issued stock-based compensation awards in the form of restricted stock and restricted stock units which, in accordance with GAAP, are considered participating securities.

Stock-based compensation awards and warrants to purchase common stock of M&T representing 408,657 and 2,015,870 common shares during the three-month periods ended September 30, 2017 and 2016, respectively, and 404,487 and 2,513,288 common shares during the nine-month periods ended September 30, 2017 and 2016, respectively, were not included in the computations of diluted earnings per common share because the effect on those periods would have been antidilutive.

Comprehensive income

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Comprehensive income

9. Comprehensive income

The following tables display the components of other comprehensive income (loss) and amounts reclassified from accumulated other comprehensive income (loss) to net income:

	Investment Securities						Defined Benefit						Total Amount				Income
	With OTTI (a)			All Other			Plans			Other			Before Tax				Tax			Net
	(In thousands)

Balance — January 1, 2017	$	46,725			(73,785	)		(449,917	)		(8,268	)	$	(485,245	)			190,609		$	(294,636	)
Other comprehensive income before reclassifications:
Unrealized holding gains (losses), net		(7,365	)		60,586			—			—			53,221				(20,934	)		32,287
Foreign currency translation adjustment		—			—			—			3,829			3,829				(1,340	)		2,489
Unrealized losses on cash flow hedges		—			—			—			(1,076	)		(1,076	)			424			(652	)
Total other comprehensive income (loss) before reclassifications		(7,365	)		60,586			—			2,753			55,974				(21,850	)		34,124
Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities		—			2,535			—			—			2,535		(b)		(998	)		1,537
(Gains) losses realized in net income		(50	)		67			—			—			17		(c)		(7	)		10
Accretion of net gain on terminated cash flow hedges		—			—			—			(109	)		(109	)	(d)		43			(66	)
Net yield adjustment from cash flow hedges currently in effect		—			—			—			(2,275	)		(2,275	)	(b)		895			(1,380	)
Amortization of prior service credit		—			—			(601	)		—			(601	)	(e)		236			(365	)
Amortization of actuarial losses		—			—			21,206			—			21,206		(e)		(8,345	)		12,861
Total reclassifications		(50	)		2,602			20,605			(2,384	)		20,773				(8,176	)		12,597
Total gain (loss) during the period		(7,415	)		63,188			20,605			369			76,747				(30,026	)		46,721
Balance — September 30, 2017	$	39,310			(10,597	)		(429,312	)		(7,899	)	$	(408,498	)			160,583		$	(247,915	)

Balance — January 1, 2016	$	16,359			62,849			(489,660	)		(4,093	)	$	(414,545	)			162,918		$	(251,627	)
Other comprehensive income before reclassifications:
Unrealized holding gains, net		1,228			234,438			—			—			235,666				(92,714	)		142,952
Foreign currency translation adjustment		—			—			—			(2,836	)		(2,836	)			989			(1,847	)
Total other comprehensive income (loss) before reclassifications		1,228			234,438			—			(2,836	)		232,830				(91,725	)		141,105
Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
Amortization of unrealized holding losses on HTM securities		—			2,998			—			—			2,998		(b)		(1,180	)		1,818
Gains realized in net income		—			(28,748	)		—			—			(28,748	)	(c)		11,309			(17,439	)
Accretion of net gain on terminated cash flow hedges		—			—			—			(116	)		(116	)	(d)		46			(70	)
Amortization of prior service credit		—			—			(3,440	)		—			(3,440	)	(e)		1,354			(2,086	)
Amortization of actuarial losses		—			—			22,654			—			22,654		(e)		(8,914	)		13,740
Total reclassifications		—			(25,750	)		19,214			(116	)		(6,652	)			2,615			(4,037	)
Total gain (loss) during the period		1,228			208,688			19,214			(2,952	)		226,178				(89,110	)		137,068
Balance — September 30, 2016	$	17,587			271,537			(470,446	)		(7,045	)	$	(188,367	)			73,808		$	(114,559	)

(a)	Other-than-temporary impairment

(b)	Included in interest income

(c)	Included in gain (loss) on bank investment securities

(d)	Included in interest expense

(e)	Included in salaries and employee benefits expense

9. Comprehensive income, continued

Accumulated other comprehensive income (loss), net consisted of the following:

	Investment Securities						Defined Benefit
	With OTTI			All Other			Plans			Other			Total
	(In thousands)

Balance — December 31, 2016	$	28,338			(44,657	)		(272,874	)		(5,443	)	$	(294,636	)
Net gain (loss) during period		(4,496	)		38,330			12,496			391			46,721
Balance — September 30, 2017	$	23,842			(6,327	)		(260,378	)		(5,052	)	$	(247,915	)

Derivative financial instruments

9 Months Ended

Sep. 30, 2017

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Derivative financial instruments

10. Derivative financial instruments

As part of managing interest rate risk, the Company enters into interest rate swap agreements to modify the repricing characteristics of certain portions of the Company’s portfolios of earning assets and interest-bearing liabilities. The Company designates interest rate swap agreements utilized in the management of interest rate risk as either fair value hedges or cash flow hedges. Interest rate swap agreements are generally entered into with counterparties that meet established credit standards and most contain master netting, collateral and/or settlement provisions protecting the at-risk party. Based on adherence to the Company’s credit standards and the presence of the netting, collateral or settlement provisions, the Company believes that the credit risk inherent in these contracts was not significant as of September 30, 2017.

The net effect of interest rate swap agreements was to increase net interest income by $7 million and $9 million for the three-month periods ended September 30, 2017 and 2016, respectively, and $18 million and $30 million for the nine-month periods ended September 30, 2017 and 2016, respectively.

Information about interest rate swap agreements entered into for interest rate risk management purposes summarized by type of financial instrument the swap agreements were intended to hedge follows:

					Weighted- Average Rate
	Notional Amount		Average Maturity		Fixed			Variable			Estimated Fair Value Gain (a)
	(In thousands)		(In years)								(In thousands)
September 30, 2017
Fair value hedges:
Fixed rate long-term borrowings (b)	$	4,950,000		2.9		2.63	%		2.04	%	$	697
Cash flow hedges:
Variable rate commercial real estate loans (b)		2,000,000		1.6		1.46	%		1.24	%		—
Total	$	6,950,000		2.5							$	697
December 31, 2016
Fair value hedges:
Fixed rate long-term borrowings (b)	$	900,000		1.1		3.75	%		2.08	%	$	11,892

(a)

Effective January 2017 certain clearinghouse exchanges revised their rules such that certain required payments by counterparties for variation margin on derivative instruments that had been treated as collateral are now treated as settlements of those positions. The impact of such rule changes at September 30, 2017 was a reduction of the estimated fair value losses on interest rate swaps designated as fair value hedges of $12.2 million and on interest rate swaps designated as cash flow hedges of $3.4 million.

(b)	Under the terms of these agreements, the Company receives settlement amounts at a fixed rate and pays at a variable rate.

10. Derivative financial instruments, continued

The Company utilizes commitments to sell residential and commercial real estate loans to hedge the exposure to changes in the fair value of real estate loans held for sale. Such commitments have generally been designated as fair value hedges. The Company also utilizes commitments to sell real estate loans to offset the exposure to changes in fair value of certain commitments to originate real estate loans for sale.

Derivative financial instruments used for trading account purposes included interest rate contracts, foreign exchange and other option contracts, foreign exchange forward and spot contracts, and financial futures. Interest rate contracts entered into for trading account purposes had notional values of $15.5 billion and $21.6 billion at September 30, 2017 and December 31, 2016, respectively. The notional amounts of foreign currency and other option and futures contracts entered into for trading account purposes aggregated $545 million and $471 million at September 30, 2017 and December 31, 2016, respectively.

Information about the fair values of derivative instruments in the Company’s consolidated balance sheet and consolidated statement of income follows:

	Asset Derivatives				Liability Derivatives
	Fair Value				Fair Value
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
	(In thousands)
Derivatives designated and qualifying as hedging instruments
Fair value hedges:
Interest rate swap agreements (a)	$	2,048	$	11,892	$	1,351	$	—
Commitments to sell real estate loans (a)		1,667		33,189		1,551		1,347
Cash flow hedges:
Interest rate swap agreements (a)		—		—		—		—
		3,715		45,081		2,902		1,347
Derivatives not designated and qualifying as hedging instruments
Mortgage-related commitments to originate real estate loans for sale (a)		13,962		8,060		240		735
Commitments to sell real estate loans (a)		3,153		5,210		936		399
Trading:
Interest rate contracts (b)		104,178		228,810		103,825		167,737
Foreign exchange and other option and futures contracts (b)		6,823		7,908		5,905		6,639
		128,116		249,988		110,906		175,510
Total derivatives	$	131,831	$	295,069	$	113,808	$	176,857

(a)	Asset derivatives are reported in other assets and liability derivatives are reported in other liabilities.

(b)

Asset derivatives are reported in trading account assets and liability derivatives are reported in other liabilities. The impact of the variation margin rule change at September 30, 2017 was a reduction of the estimated fair value of interest rate swaps in an asset position of $89.3 million and of those in a liability position of $29.2 million.

10. Derivative financial instruments, continued

	Amount of Gain (Loss) Recognized
	Three Months Ended September 30, 2017					Three Months Ended September 30, 2016
	Derivative			Hedged Item		Derivative			Hedged Item
	(In thousands)
Derivatives in fair value hedging relationships
Interest rate swap agreements:
Fixed rate long-term borrowings (a)	$	(13,509	)		14,026	$	(12,588	)		12,587
Derivatives not designated as hedging instruments
Trading:
Interest rate contracts (b)	$	(418	)			$	4,822
Foreign exchange and other option and futures contracts (b)		1,362					1,746
Total	$	944				$	6,568

	Amount of Gain (Loss) Recognized
	Nine Months Ended September 30, 2017					Nine Months Ended September 30, 2016
	Derivative			Hedged Item		Derivative			Hedged Item
	(In thousands)
Derivatives in fair value hedging relationships
Interest rate swap agreements:
Fixed rate long-term borrowings (a)	$	(23,423	)		23,049	$	(22,832	)		21,603
Derivatives not designated as hedging instruments
Trading:
Interest rate contracts (b)	$	2,363				$	11,578
Foreign exchange and other option and futures contracts (b)		4,766					5,415
Total	$	7,129				$	16,993

(a)

Reported as other revenues from operations.

(b)

Reported as trading account and foreign exchange gains.

The amount of gain (loss) recognized in the consolidated statement of income associated with derivatives designated as cash flow hedges was not material for the three and nine months ended September 30, 2017.

The Company also has commitments to sell and commitments to originate residential and commercial real estate loans that are considered derivatives. The Company designates certain of the commitments to sell real estate loans as fair value hedges of real estate loans held for sale. The Company also utilizes commitments to sell real estate loans to offset the exposure to changes in the fair value of certain commitments to originate real estate loans for sale. As a result of these activities, net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans were approximately $27 million and $28 million at September 30, 2017 and December 31, 2016, respectively. Changes in unrealized gains and losses are included in mortgage banking revenues and, in general, are realized in subsequent periods as the related loans are sold and commitments satisfied.

The Company does not offset derivative asset and liability positions in its consolidated financial statements. The Company’s exposure to credit risk by entering into derivative contracts is mitigated through master netting agreements and collateral posting or settlement requirements. Master netting agreements covering interest rate and foreign exchange contracts with the same party include a right to set-off that becomes enforceable in the event of default, early termination or under other specific conditions.

10. Derivative financial instruments, continued

The aggregate fair value of derivative financial instruments in a liability position which are subject to enforceable master netting arrangements was $17 million and $34 million at September 30, 2017 and December 31, 2016, respectively. After consideration of such netting arrangements for purposes of posting collateral, the net liability positions with counterparties aggregated $17 million and $30 million at September 30, 2017 and December 31, 2016, respectively. The Company was required to post collateral relating to those positions of $18 million and $27 million at September 30, 2017 and December 31, 2016, respectively. Certain of the Company’s derivative financial instruments contain provisions that require the Company to maintain specific credit ratings from credit rating agencies to avoid higher collateral posting requirements. If the Company’s debt rating were to fall below specified ratings, the counterparties of the derivative financial instruments could demand immediate incremental collateralization on those instruments in a net liability position. The aggregate fair value of all derivative financial instruments with such credit risk-related contingent features in a net liability position on September 30, 2017 was less than $1 million, for which the Company was not required to post collateral in the normal course of business. If the credit risk-related contingent features had been triggered on September 30, 2017, the Company would not have been required to post any collateral to counterparties.

The aggregate fair value of derivative financial instruments in an asset position, which are subject to enforceable master netting arrangements, was $7 million and $15 million at September 30, 2017 and December 31, 2016, respectively. After consideration of such netting arrangements for purposes of posting collateral, the net asset positions with counterparties aggregated $7 million and $11 million at September 30, 2017 and December 31, 2016, respectively. Counterparties posted collateral relating to those positions of $5 million and $9 million at September 30, 2017 and December 31, 2016, respectively. Trading account interest rate swap agreements entered into with customers are subject to the Company’s credit risk standards and often contain collateral provisions.

In addition to the derivative contracts noted above, the Company clears certain derivative transactions through a clearinghouse, rather than directly with counterparties. Those transactions cleared through a clearinghouse require initial margin collateral and variation margin payments depending on the contracts being in a net asset or liability position. The amount of initial margin collateral posted by the Company was $49 million and $111 million at September 30, 2017 and December 31, 2016, respectively. The fair value asset and liability amounts of derivative contracts at September 30, 2017 have been reduced by variation margin payments treated as settlements of $89 million and $45 million, respectively. Variation margin on derivative contracts not treated as settlements continues to represent collateral posted or received by the Company. For those contracts, the net fair values of derivative financial instruments cleared through clearinghouses for which variation margin is required was a net asset position of $1 million and $63 million at September 30, 2017 and December 31, 2016, respectively. Collateral posted by the clearinghouses associated with that net asset position was $1 million and $81 million at September 30, 2017 and December 31, 2016, respectively.

Variable interest entities and asset securitizations	9 Months Ended
Variable interest entities and asset securitizations	Sep. 30, 2017
Text Block [Abstract]
Variable interest entities and asset securitizations	11. Variable interest entities and asset securitizations As described in note 5, M&T has issued junior subordinated debentures payable to various trusts that have issued Capital Securities. M&T owns the common securities of those trust entities. The Company is not considered to be the primary beneficiary of those entities and, accordingly, the trusts are not included in the Company’s consolidated financial statements. At September 30, 2017 and December 31, 2016, the Company included the junior subordinated debentures as “long-term borrowings” in its consolidated balance sheet and recognized $24 million in other assets for its “investment” in the common securities of the trusts that will be concomitantly repaid to M&T by the respective trust from the proceeds of M&T’s repayment of the junior subordinated debentures associated with preferred capital securities described in note 5. 11. Variable interest entities and asset securitizations, continued The Company has invested as a limited partner in various partnerships that collectively had total assets of approximately $1.0 billion at September 30, 2017 and December 31, 2016. Those partnerships generally construct or acquire properties for which the investing partners are eligible to receive certain federal income tax credits in accordance with government guidelines. Such investments may also provide tax deductible losses to the partners. The partnership investments also assist the Company in achieving its community reinvestment initiatives. As a limited partner, there is no recourse to the Company by creditors of the partnerships. However, the tax credits that result from the Company’s investments in such partnerships are generally subject to recapture should a partnership fail to comply with the respective government regulations. The Company’s maximum exposure to loss of its investments in such partnerships was $329 million, including $118 million of unfunded commitments, at September 30, 2017 and $294 million, including $102 million of unfunded commitments, at December 31, 2016. Contingent commitments to provide additional capital contributions to these partnerships were not material at September 30, 2017. The Company has not provided financial or other support to the partnerships that was not contractually required. Management currently estimates that no material losses are probable as a result of the Company’s involvement with such entities. The Company, in its position as limited partner, does not direct the activities that most significantly impact the economic performance of the partnerships and, therefore, in accordance with the accounting provisions for variable interest entities, the partnership entities are not included in the Company’s consolidated financial statements. The Company’s investment cost is amortized to income taxes in the consolidated statement of income as tax credits and other tax benefits resulting from deductible losses associated with the projects are received. The Company amortized $11 million and $35 million of its investments in qualified affordable housing projects to income tax expense during the three-month and nine-month periods ended September 30, 2017, respectively, and recognized $16 million and $47 million of tax credits and other tax benefits during those respective periods. Similarly, for the three-month and nine-month periods ended September 30, 2016, the Company amortized $13 million and $34 million, respectively, of its investments in qualified affordable housing projects to income tax expense and recognized $18 million and $46 million of tax credits and other tax benefits during those respective periods. The Company serves as investment advisor for certain registered money-market funds. The Company has no explicit arrangement to provide support to those funds, but may waive portions of its allowable management fees as a result of market conditions.

Fair value measurements

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair value measurements

12. Fair value measurements

GAAP permits an entity to choose to measure eligible financial instruments and other items at fair value. The Company has not made any fair value elections at September 30, 2017.

Pursuant to GAAP, fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three-level hierarchy exists in GAAP for fair value measurements based upon the inputs to the valuation of an asset or liability.

•

Level 1 — Valuation is based on quoted prices in active markets for identical assets and liabilities.

•

Level 2 — Valuation is determined from quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar instruments in markets that are not active or by model-based techniques in which all significant inputs are observable in the market.

•

Level 3 — Valuation is derived from model-based and other techniques in which at least one significant input is unobservable and which may be based on the Company's own estimates about the assumptions that market participants would use to value the asset or liability.

When available, the Company attempts to use quoted market prices in active markets to determine fair value and classifies such items as Level 1 or Level 2. If quoted market prices in active markets are not available, fair value

12. Fair value measurements, continued

is often determined using model-based techniques incorporating various assumptions including interest rates, prepayment speeds and credit losses. Assets and liabilities valued using model-based techniques are classified as either Level 2 or Level 3, depending on the lowest level classification of an input that is considered significant to the overall valuation. The following is a description of the valuation methodologies used for the Company's assets and liabilities that are measured on a recurring basis at estimated fair value.

Trading account assets and liabilities

Trading account assets and liabilities consist primarily of interest rate swap agreements and foreign exchange contracts with customers who require such services with offsetting positions with third parties to minimize the Company's risk with respect to such transactions. The Company generally determines the fair value of its derivative trading account assets and liabilities using externally developed pricing models based on market observable inputs and, therefore, classifies such valuations as Level 2. Mutual funds held in connection with deferred compensation and other arrangements have been classified as Level 1 valuations. Valuations of investments in municipal and other bonds can generally be obtained through reference to quoted prices in less active markets for the same or similar securities or through model-based techniques in which all significant inputs are observable and, therefore, such valuations have been classified as Level 2.

Investment securities available for sale

The majority of the Company's available-for-sale investment securities have been valued by reference to prices for similar securities or through model-based techniques in which all significant inputs are observable and, therefore, such valuations have been classified as Level 2. Certain investments in mutual funds and equity securities are actively traded and, therefore, have been classified as Level 1 valuations.

Real estate loans held for sale

The Company utilizes commitments to sell real estate loans to hedge the exposure to changes in fair value of real estate loans held for sale. The carrying value of hedged real estate loans held for sale includes changes in estimated fair value during the hedge period. Typically, the Company attempts to hedge real estate loans held for sale from the date of close through the sale date. The fair value of hedged real estate loans held for sale is generally calculated by reference to quoted prices in secondary markets for commitments to sell real estate loans with similar characteristics and, accordingly, such loans have been classified as a Level 2 valuation.

Commitments to originate real estate loans for sale and commitments to sell real estate loans

The Company enters into various commitments to originate real estate loans for sale and commitments to sell real estate loans. Such commitments are considered to be derivative financial instruments and, therefore, are carried at estimated fair value on the consolidated balance sheet. The estimated fair values of such commitments were generally calculated by reference to quoted prices in secondary markets for commitments to sell real estate loans to certain government-sponsored entities and other parties. The fair valuations of commitments to sell real estate loans generally result in a Level 2 classification. The estimated fair value of commitments to originate real estate loans for sale are adjusted to reflect the Company's anticipated commitment expirations. The estimated commitment expirations are considered significant unobservable inputs contributing to the Level 3 classification of commitments to originate real estate loans for sale. Significant unobservable inputs used in the determination of estimated fair value of commitments to originate real estate loans for sale are included in the accompanying table of significant unobservable inputs to Level 3 measurements.

Interest rate swap agreements used for interest rate risk management

The Company utilizes interest rate swap agreements as part of the management of interest rate risk to modify the repricing characteristics of certain portions of its portfolios of earning assets and interest-bearing liabilities. The Company generally determines the fair value of its interest rate swap agreements using externally developed pricing

12. Fair value measurements, continued

models based on market observable inputs and, therefore, classifies such valuations as Level 2. The Company has considered counterparty credit risk in the valuation of its interest rate swap agreement assets and has considered its own credit risk in the valuation of its interest rate swap agreement liabilities.

The following tables present assets and liabilities at September 30, 2017 and December 31, 2016 measured at estimated fair value on a recurring basis:

	Fair Value Measurements		Level 1 (a)		Level 2 (a)		Level 3
	(In thousands)
September 30, 2017
Trading account assets	$	170,516		47,927		122,589		—
Investment securities available for sale:
U.S. Treasury and federal agencies		2,007,117		—		2,007,117		—
Obligations of states and political subdivisions		2,678		—		2,678		—
Mortgage-backed securities:
Government issued or guaranteed		9,184,483		—		9,184,483		—
Privately issued		30		—		—		30
Other debt securities		128,530		—		128,530		—
Equity securities		93,986		50,917		43,069		—
		11,416,824		50,917		11,365,877		30
Real estate loans held for sale		571,199		—		571,199		—
Other assets (b)		20,830		—		6,868		13,962
Total assets	$	12,179,369		98,844		12,066,533		13,992
Trading account liabilities	$	109,730		—		109,730		—
Other liabilities (b)		4,078		—		3,838		240
Total liabilities	$	113,808		—		113,568		240

December 31, 2016
Trading account assets	$	323,867		46,135		277,732		—
Investment securities available for sale:
U.S. Treasury and federal agencies		1,902,544		—		1,902,544		—
Obligations of states and political subdivisions		3,641		—		3,641		—
Mortgage-backed securities:
Government issued or guaranteed		10,954,861		—		10,954,861		—
Privately issued		44		—		—		44
Other debt securities		118,516		—		118,516		—
Equity securities		352,466		301,711		50,755		—
		13,332,072		301,711		13,030,317		44
Real estate loans held for sale		1,056,180		—		1,056,180		—
Other assets (b)		58,351		—		50,291		8,060
Total assets	$	14,770,470		347,846		14,414,520		8,104
Trading account liabilities	$	174,376		—		174,376		—
Other liabilities (b)		2,481		—		1,746		735
Total liabilities	$	176,857		—		176,122		735

(a)	There were no significant transfers between Level 1 and Level 2 of the fair value hierarchy during the nine months ended September 30, 2017 and the year ended December 31, 2016.

(b)	Comprised predominantly of interest rate swap agreements used for interest rate risk management (Level 2), commitments to sell real estate loans (Level 2) and commitments to originate real estate loans to be held for sale (Level 3).

12. Fair value measurements, continued

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the three months ended September 30, 2017 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Other Assets and Other Liabilities
	(In thousands)

Balance — June 30, 2017	$	35			12,425
Total gains (losses) realized/unrealized:
Included in earnings		—			22,313		(b)
Settlements		(5	)		—
Transfers in and/or out of Level 3 (a)		—			(21,016	)	(d)
Balance — September 30, 2017	$	30			13,722
Changes in unrealized gains included in earnings related to assets still held at September 30, 2017	$	—			12,659		(b)

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the three months ended September 30, 2016 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Collateralized Debt Obligations				Other Assets and Other Liabilities
	(In thousands)

Balance — June 30, 2016	$	57			43,305				21,383
Total gains (losses) realized/unrealized:
Included in earnings		—			28,475				45,534		(b)
Included in other comprehensive income		—			(15,050	)	(c)		—
Sales		—			(56,730	)			—
Settlements		(6	)		—				—
Transfers in and/or out of Level 3 (a)		—			—				(37,117	)	(d)
Balance — September 30, 2016	$	51			—				29,800
Changes in unrealized gains included in earnings related to assets still held at September 30, 2016	$	—			—				27,663		(b)

12. Fair value measurements, continued

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the nine months ended September 30, 2017 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Other Assets and Other Liabilities
	(In thousands)

Balance — January 1, 2017	$	44			7,325
Total gains (losses) realized/unrealized:
Included in earnings		—			65,824		(b)
Settlements		(14	)		—
Transfers in and/or out of Level 3 (a)		—			(59,427	)	(d)
Balance — September 30, 2017	$	30		$	13,722
Changes in unrealized gains included in earnings related to assets still held at September 30, 2017	$	—		$	13,684		(b)

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the nine months ended September 30, 2016 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Collateralized Debt Obligations				Other Assets and Other Liabilities
				(In thousands)

Balance — January 1, 2016	$	74			47,393				9,879
Total gains (losses) realized/unrealized:
Included in earnings		—			28,475				104,862		(b)
Included in other comprehensive income		—			(18,268	)	(c)		—
Sales		—			(56,730	)			—
Settlements		(23	)		(870	)			—
Transfers in and/or out of Level 3 (a)		—			—				(84,941	)	(d)
Balance — September 30, 2016	$	51			—				29,800
Changes in unrealized gains included in earnings related to assets still held at September 30, 2016	$	—			—				29,288		(b)

(a)	The Company’s policy for transfers between fair value levels is to recognize the transfer as of the actual date of the event or change in circumstances that caused the transfer.

(b)	Reported as mortgage banking revenues in the consolidated statement of income and includes the fair value of commitment issuances and expirations.

(c)	Reported as net unrealized losses on investment securities in the consolidated statement of comprehensive income. The Company sold its collateralized debt obligations during the third and fourth quarters of 2016.

(d)	Transfers out of Level 3 consist of interest rate locks transferred to closed loans.

12. Fair value measurements, continued

The Company is required, on a nonrecurring basis, to adjust the carrying value of certain assets or provide valuation allowances related to certain assets using fair value measurements. The more significant of those assets follow.

Loans

Loans are generally not recorded at fair value on a recurring basis. Periodically, the Company records nonrecurring adjustments to the carrying value of loans based on fair value measurements for partial charge-offs of the uncollectible portions of those loans. Nonrecurring adjustments also include certain impairment amounts for collateral-dependent loans when establishing the allowance for credit losses. Such amounts are generally based on the fair value of the underlying collateral supporting the loan and, as a result, the carrying value of the loan less the calculated valuation amount does not necessarily represent the fair value of the loan. Real estate collateral is typically valued using appraisals or other indications of value based on recent comparable sales of similar properties or assumptions generally observable in the marketplace and the related nonrecurring fair value measurement adjustments have generally been classified as Level 2, unless significant adjustments have been made to the valuation that are not readily observable by market participants. Non-real estate collateral supporting commercial loans generally consists of business assets such as receivables, inventory and equipment. Fair value estimations are typically determined by discounting recorded values of those assets to reflect estimated net realizable value considering specific borrower facts and circumstances and the experience of credit personnel in their dealings with similar borrower collateral liquidations. Such discounts were generally in the range of 15% to 90% at September 30, 2017. As these discounts are not readily observable and are considered significant, the valuations have been classified as Level 3. Automobile collateral is typically valued by reference to independent pricing sources based on recent sales transactions of similar vehicles, and the related nonrecurring fair value measurement adjustments have been classified as Level 2. Collateral values for other consumer installment loans are generally estimated based on historical recovery rates for similar types of loans. As these recovery rates are not readily observable by market participants, such valuation adjustments have been classified as Level 3. Loans subject to nonrecurring fair value measurement were $184 million at September 30, 2017 ($105 million and $79 million of which were classified as Level 2 and Level 3, respectively), $293 million at December 31, 2016 ($153 million and $140 million of which were classified as Level 2 and Level 3, respectively) and $249 million at September 30, 2016 ($144 million and $105 million of which were classified as Level 2 and Level 3, respectively). Changes in fair value recognized for partial charge-offs of loans and loan impairment reserves on loans held by the Company on September 30, 2017 were decreases of $16 million and $55 million for the three-month and nine-month periods ended September 30, 2017, respectively. Changes in fair value recognized for partial charge-offs of loans and loan impairment reserves on loans held by the Company on September 30, 2016 were decreases of $20 million and $42 million for the three-month and nine-month periods ended September 30, 2016, respectively.

Assets taken in foreclosure of defaulted loans

Assets taken in foreclosure of defaulted loans are primarily comprised of commercial and residential real property and are generally measured at the lower of cost or fair value less costs to sell. The fair value of the real property is generally determined using appraisals or other indications of value based on recent comparable sales of similar properties or assumptions generally observable in the marketplace and the related nonrecurring fair value measurement adjustments have generally been classified as Level 2. Assets taken in foreclosure of defaulted loans subject to nonrecurring fair value measurement were $36 million and $53 million at September 30, 2017 and 2016, respectively. Changes in fair value recognized for those foreclosed assets held by the Company were not material during the three-month and nine-month periods ended September 30, 2017 and 2016.

12. Fair value measurements, continued

Significant unobservable inputs to Level 3 measurements

The following tables present quantitative information about significant unobservable inputs used in the fair value measurements for certain Level 3 assets and liabilities at September 30, 2017 and December 31, 2016:

Fair Value

Valuation

Technique

Unobservable

Inputs/Assumptions

Range

(Weighted-

Average)

(In thousands)

September 30, 2017

Recurring fair value measurements

Privately issued mortgage-backed

securities

Two independent pricing quotes

—

Net other assets (liabilities) (a)

13,722

Discounted cash flow

Commitment expirations

0%-80% (28%)

December 31, 2016

Recurring fair value measurements

Privately issued mortgage-backed

securities

Two independent pricing quotes

—

Net other assets (liabilities) (a)

7,325

Discounted cash flow

Commitment expirations

0%-77% (30%)

(a)	Other Level 3 assets (liabilities) consist of commitments to originate real estate loans.

Sensitivity of fair value measurements to changes in unobservable inputs

An increase (decrease) in the estimate of expirations for commitments to originate real estate loans would generally result in a lower (higher) fair value measurement. Estimated commitment expirations are derived considering loan type, changes in interest rates and remaining length of time until closing.

12. Fair value measurements, continued

Disclosures of fair value of financial instruments

The carrying amounts and estimated fair value for financial instrument assets (liabilities) are presented in the following table:

	September 30, 2017
	Carrying Amount			Estimated Fair Value			Level 1		Level 2			Level 3
	(In thousands)
Financial assets:
Cash and cash equivalents	$	1,368,252			1,368,252			1,290,532		77,720			—
Interest-bearing deposits at banks		6,306,484			6,306,484			—		6,306,484			—
Trading account assets		170,516			170,516			47,927		122,589			—
Investment securities		15,073,926			15,079,756			50,917		14,916,360			112,479
Loans and leases:
Commercial loans and leases		21,743,251			21,409,984			—		—			21,409,984
Commercial real estate loans		32,914,288			32,507,319			—		223,659			32,283,660
Residential real estate loans		20,265,162			20,369,392			—		4,557,929			15,811,463
Consumer loans		13,002,433			12,935,924			—		—			12,935,924
Allowance for credit losses		(1,013,326	)		—			—		—			—
Loans and leases, net		86,911,808			87,222,619			—		4,781,588			82,441,031
Accrued interest receivable		325,982			325,982			—		325,982			—
Financial liabilities:
Noninterest-bearing deposits	$	(33,111,246	)		(33,111,246	)		—		(33,111,246	)		—
Savings and interest-checking deposits		(52,936,615	)		(52,936,615	)		—		(52,936,615	)		—
Time deposits		(7,233,518	)		(7,294,182	)		—		(7,294,182	)		—
Deposits at Cayman Islands office		(232,014	)		(232,014	)		—		(232,014	)		—
Short-term borrowings		(200,768	)		(200,768	)		—		(200,768	)		—
Long-term borrowings		(8,577,645	)		(8,630,195	)		—		(8,630,195	)		—
Accrued interest payable		(69,290	)		(69,290	)		—		(69,290	)		—
Trading account liabilities		(109,730	)		(109,730	)		—		(109,730	)		—
Other financial instruments:
Commitments to originate real estate loans for sale	$	13,722			13,722			—		—			13,722
Commitments to sell real estate loans		2,333			2,333			—		2,333			—
Other credit-related commitments		(119,938	)		(119,938	)		—		—			(119,938	)
Interest rate swap agreements used for interest rate risk management		697			697			—		697			—

12. Fair value measurements, continued

	December 31, 2016
	Carrying Amount			Estimated Fair Value			Level 1		Level 2			Level 3
				(In thousands)
Financial assets:
Cash and cash equivalents	$	1,320,549			1,320,549			1,249,654		70,895		—
Interest-bearing deposits at banks		5,000,638			5,000,638			—		5,000,638		—
Trading account assets		323,867			323,867			46,135		277,732		—
Investment securities		16,250,468			16,244,412			301,711		15,821,176			121,525
Loans and leases:
Commercial loans and leases		22,610,047			22,239,428		—		—				22,239,428
Commercial real estate loans		33,506,394			33,129,428		—			642,590			32,486,838
Residential real estate loans		22,590,912			22,638,167		—			4,912,488			17,725,679
Consumer loans		12,146,063			12,061,590		—			—			12,061,590
Allowance for credit losses		(988,997	)		—		—			—			—
Loans and leases, net		89,864,419			90,068,613		—			5,555,078			84,513,535
Accrued interest receivable		308,805			308,805		—			308,805		—
Financial liabilities:
Noninterest-bearing deposits	$	(32,813,896	)		(32,813,896	)	—			(32,813,896	)	—
Savings and interest-checking deposits		(52,346,207	)		(52,346,207	)	—			(52,346,207	)	—
Time deposits		(10,131,846	)		(10,222,585	)	—			(10,222,585	)	—
Deposits at Cayman Islands office		(201,927	)		(201,927	)	—			(201,927	)	—
Short-term borrowings		(163,442	)		(163,442	)	—			(163,442	)	—
Long-term borrowings		(9,493,835	)		(9,473,844	)	—			(9,473,844	)	—
Accrued interest payable		(75,172	)		(75,172	)	—			(75,172	)	—
Trading account liabilities		(174,376	)		(174,376	)	—			(174,376	)	—
Other financial instruments:
Commitments to originate real estate loans for sale	$	7,325			7,325		—			—			7,325
Commitments to sell real estate loans		36,653			36,653		—			36,653		—
Other credit-related commitments		(136,295	)		(136,295	)	—			—			(136,295	)
Interest rate swap agreements used for interest rate risk management		11,892			11,892		—			11,892		—

With the exception of marketable securities, certain off-balance sheet financial instruments and mortgage loans originated for sale, the Company’s financial instruments are not readily marketable and market prices do not exist. The Company, in attempting to comply with the provisions of GAAP that require disclosures of fair value of financial instruments, has not attempted to market its financial instruments to potential buyers, if any exist. Since negotiated prices in illiquid markets depend greatly upon the then present motivations of the buyer and seller, it is reasonable to assume that actual sales prices could vary widely from any estimate of fair value made without the benefit of negotiations. Additionally, changes in market interest rates can dramatically impact the value of financial instruments in a short period of time. The following assumptions, methods and calculations were used in determining the estimated fair value of financial instruments not measured at fair value in the consolidated balance sheet.

Cash and cash equivalents, interest-bearing deposits at banks, deposits at Cayman Islands office, short-term borrowings, accrued interest receivable and accrued interest payable

Due to the nature of cash and cash equivalents and the near maturity of interest-bearing deposits at banks, deposits at Cayman Islands office, short-term borrowings, accrued interest receivable and accrued interest payable, the Company estimated that the carrying amount of such instruments approximated estimated fair value.

12. Fair value measurements, continued

Investment securities

Estimated fair values of investments in readily marketable securities were generally based on quoted market prices. Investment securities that were not readily marketable were assigned amounts based on estimates provided by outside parties or modeling techniques that relied upon discounted calculations of projected cash flows or, in the case of other investment securities, which include capital stock of the Federal Reserve Bank of New York and the Federal Home Loan Bank of New York, at an amount equal to the carrying amount.

Loans and leases

In general, discount rates used to calculate values for loan products were based on the Company’s pricing at the respective period end. A higher discount rate was assumed with respect to estimated cash flows associated with nonaccrual loans. Projected loan cash flows were adjusted for estimated credit losses. However, such estimates made by the Company may not be indicative of assumptions and adjustments that a purchaser of the Company’s loans and leases would seek.

Deposits

Pursuant to GAAP, the estimated fair value ascribed to noninterest-bearing deposits, savings deposits and interest-checking deposits must be established at carrying value because of the customers’ ability to withdraw funds immediately. Time deposit accounts are required to be revalued based upon prevailing market interest rates for similar maturity instruments. As a result, amounts assigned to time deposits were based on discounted cash flow calculations using prevailing market interest rates based on the Company’s pricing at the respective date for deposits with comparable remaining terms to maturity.

The Company believes that deposit accounts have a value greater than that prescribed by GAAP. The Company feels, however, that the value associated with these deposits is greatly influenced by characteristics of the buyer, such as the ability to reduce the costs of servicing the deposits and deposit attrition which often occurs following an acquisition.

Long-term borrowings

The amounts assigned to long-term borrowings were based on quoted market prices, when available, or were based on discounted cash flow calculations using prevailing market interest rates for borrowings of similar terms and credit risk.

Other commitments and contingencies

As described in note 13, in the normal course of business, various commitments and contingent liabilities are outstanding, such as loan commitments, credit guarantees and letters of credit. The Company’s pricing of such financial instruments is based largely on credit quality and relationship, probability of funding and other requirements. Loan commitments often have fixed expiration dates and contain termination and other clauses which provide for relief from funding in the event of significant deterioration in the credit quality of the customer. The rates and terms of the Company’s loan commitments, credit guarantees and letters of credit are competitive with other financial institutions operating in markets served by the Company. The Company believes that the carrying amounts, which are included in other liabilities, are reasonable estimates of the fair value of these financial instruments.

12. Fair value measurements, continued

The Company does not believe that the estimated information presented herein is representative of the earnings power or value of the Company. The preceding analysis, which is inherently limited in depicting fair value, also does not consider any value associated with existing customer relationships nor the ability of the Company to create value through loan origination, deposit gathering or fee generating activities. Many of the estimates presented herein are based upon the use of highly subjective information and assumptions and, accordingly, the results may not be precise. Management believes that fair value estimates may not be comparable between financial institutions due to the wide range of permitted valuation techniques and numerous estimates which must be made. Furthermore, because the disclosed fair value amounts were estimated as of the balance sheet date, the amounts actually realized or paid upon maturity or settlement of the various financial instruments could be significantly different.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Commitments and contingencies

9 Months Ended

Sep. 30, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and contingencies

13. Commitments and contingencies

In the normal course of business, various commitments and contingent liabilities are outstanding. The following table presents the Company's significant commitments. Certain of these commitments are not included in the Company's consolidated balance sheet.

	September 30,		December 31,
	2017		2016
	(In thousands)
Commitments to extend credit
Home equity lines of credit	$	5,492,892		5,499,609
Commercial real estate loans to be sold		170,786		70,100
Other commercial real estate		5,749,428		6,451,709
Residential real estate loans to be sold		482,650		478,950
Other residential real estate		202,702		232,721
Commercial and other		12,677,838		12,298,473
Standby letters of credit		2,657,352		2,987,091
Commercial letters of credit		42,684		44,723
Financial guarantees and indemnification contracts		3,385,498		3,043,580
Commitments to sell real estate loans		1,052,472		1,489,237

Commitments to extend credit are agreements to lend to customers, generally having fixed expiration dates or other termination clauses that may require payment of a fee. Standby and commercial letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party. Standby letters of credit generally are contingent upon the failure of the customer to perform according to the terms of the underlying contract with the third party, whereas commercial letters of credit are issued to facilitate commerce and typically result in the commitment being funded when the underlying transaction is consummated between the customer and a third party. The credit risk associated with commitments to extend credit and standby and commercial letters of credit is essentially the same as that involved with extending loans to customers and is subject to normal credit policies. Collateral may be obtained based on management's assessment of the customer's creditworthiness.

Financial guarantees and indemnification contracts are oftentimes similar to standby letters of credit and include mandatory purchase agreements issued to ensure that customer obligations are fulfilled, recourse obligations associated with sold loans, and other guarantees of customer performance or compliance with designated rules and regulations. Included in financial guarantees and indemnification contracts are loan principal amounts sold with recourse in conjunction with the Company's involvement in the Fannie Mae Delegated Underwriting and Servicing program. The Company's maximum credit risk for recourse associated with loans sold under this program totaled approximately $3.2 billion and $2.8 billion at September 30, 2017 and December 31, 2016, respectively.

13. Commitments and contingencies, continued

Since many loan commitments, standby letters of credit, and guarantees and indemnification contracts expire without being funded in whole or in part, the contract amounts are not necessarily indicative of future cash flows.

The Company utilizes commitments to sell real estate loans to hedge exposure to changes in the fair value of real estate loans held for sale. Such commitments are considered derivatives and along with commitments to originate real estate loans to be held for sale are generally recorded in the consolidated balance sheet at estimated fair market value.

The Company also has commitments under long-term operating leases.

The Company is contractually obligated to repurchase previously sold residential real estate loans that do not ultimately meet investor sale criteria related to underwriting procedures or loan documentation. When required to do so, the Company may reimburse loan purchasers for losses incurred or may repurchase certain loans. The Company reduces residential mortgage banking revenues by an estimate for losses related to its obligations to loan purchasers. The amount of those charges is based on the volume of loans sold, the level of reimbursement requests received from loan purchasers and estimates of losses that may be associated with previously sold loans. At September 30, 2017 the Company believes that its obligation to loan purchasers was not material to the Company’s consolidated financial position.

M&T and its subsidiaries are subject in the normal course of business to various pending and threatened legal proceedings and other matters in which claims for monetary damages are asserted. On an on-going basis management, after consultation with legal counsel, assesses the Company’s liabilities and contingencies in connection with such proceedings. For those matters where it is probable that the Company will incur losses and the amounts of the losses can be reasonably estimated, the Company records an expense and corresponding liability in its consolidated financial statements. To the extent the pending or threatened litigation could result in exposure in excess of that liability, the amount of such excess is not currently estimable. Although not considered probable, the range of reasonably possible losses for such matters in the aggregate, beyond the existing recorded liability, was between $0 and $50 million. Although the Company does not believe that the outcome of pending litigations will be material to the Company’s consolidated financial position, it cannot rule out the possibility that such outcomes will be material to the consolidated results of operations for a particular reporting period in the future.

Segment information

9 Months Ended

Sep. 30, 2017

Segment Reporting [Abstract]

Segment information

14. Segment information

Reportable segments have been determined based upon the Company's internal profitability reporting system, which is organized by strategic business unit. Certain strategic business units have been combined for segment information reporting purposes where the nature of the products and services, the type of customer and the distribution of those products and services are similar. The reportable segments are Business Banking, Commercial Banking, Commercial Real Estate, Discretionary Portfolio, Residential Mortgage Banking and Retail Banking.

The financial information of the Company's segments was compiled utilizing the accounting policies described in note 22 of Notes to Financial Statements in the 2016 Annual Report. The management accounting policies and processes utilized in compiling segment financial information are highly subjective and, unlike financial accounting, are not based on authoritative guidance similar to GAAP. As a result, the financial information of the reported segments is not necessarily comparable with similar information reported by other financial institutions. Furthermore, changes in management structure or allocation methodologies and procedures may result in changes in reported segment financial data. As disclosed in the 2016 Annual Report, during 2016 the Company revised its funds transfer pricing allocation related to borrowings. Additionally, during the second quarter of 2017, the Company revised its funds transfer pricing allocation related to certain deposit categories. As a result, prior period

14. Segment information, continued

financial information has been reclassified to provide segment information on a comparable basis, as noted in the following tables.

	Three Months Ended September 30, 2016
	Total Revenues as Previously Reported		Impact of Changes			Total Revenues as Reclassified		Net Income (Loss) as Previously Reported			Impact of Changes			Net Income (Loss) as Reclassified
	(In thousands)

Business Banking	$	116,513		4,388			120,901	$	21,422			2,602			24,024
Commercial Banking		268,683		(155	)		268,528		102,796			(92	)		102,704
Commercial Real Estate		205,562		—			205,562		90,065			—			90,065
Discretionary Portfolio		114,391		(8,806	)		105,585		50,773			(5,222	)		45,551
Residential Mortgage Banking		108,576		(11,901	)		96,675		22,924			(7,059	)		15,865
Retail Banking		353,016		8,848			361,864		69,506			5,247			74,753
All Other		182,949		7,626			190,575		(7,502	)		4,524			(2,978	)
Total	$	1,349,690		—			1,349,690	$	349,984			—			349,984

	Nine Months Ended September 30, 2016
	Total Revenues as Previously Reported		Impact of Changes			Total Revenues as Reclassified		Net Income (Loss) as Previously Reported			Impact of Changes			Net Income (Loss) as Reclassified
	(In thousands)

Business Banking	$	344,562		13,022			357,584	$	69,617			7,723			77,340
Commercial Banking		787,781		(423	)		787,358		309,515			(251	)		309,264
Commercial Real Estate		575,117		—			575,117		254,682			—			254,682
Discretionary Portfolio		324,195		(28,575	)		295,620		151,522			(16,947	)		134,575
Residential Mortgage Banking		309,393		(28,539	)		280,854		59,981			(16,926	)		43,055
Retail Banking		1,037,727		25,196			1,062,923		204,291			14,943			219,234
All Other		575,885		19,319			595,204		(65,065	)		11,458			(53,607	)
Total	$	3,954,660		—			3,954,660	$	984,543			—			984,543

As also described in note 22 in the 2016 Annual Report, neither goodwill nor core deposit and other intangible assets (and the amortization charges associated with such assets) resulting from acquisitions of financial institutions have been allocated to the Company's reportable segments, but are included in the “All Other” category. The Company does, however, assign such intangible assets to business units for purposes of testing for impairment.

14. Segment information, continued

Information about the Company's segments is presented in the following table:

	Three Months Ended September 30
	2017								2016
	Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)			Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)
	(In thousands)

Business Banking	$	130,501		919			31,408		$	120,901		1,086			24,024
Commercial Banking		267,822		840			109,797			268,528		950			102,704
Commercial Real Estate		212,014		401			97,295			205,562		463			90,065
Discretionary Portfolio		65,808		(12,346	)		31,515			105,585		(14,795	)		45,551
Residential Mortgage Banking		90,018		18,866			13,546			96,675		22,051			15,865
Retail Banking		392,542		2,668			96,329			361,864		3,052			74,753
All Other		257,858		(11,348	)		(23,967	)		190,575		(12,807	)		(2,978	)
Total	$	1,416,563		—			355,923		$	1,349,690		—			349,984

	Nine Months Ended September 30
	2017								2016
	Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)			Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)
	(In thousands)

Business Banking	$	375,816		2,836			85,146		$	357,584		3,274			77,340
Commercial Banking		818,846		2,603			328,211			787,358		2,917			309,264
Commercial Real Estate		604,437		1,165			269,113			575,117		1,299			254,682
Discretionary Portfolio		216,798		(37,670	)		95,200			295,620		(43,726	)		134,575
Residential Mortgage Banking		264,120		55,221			37,206			280,854		62,955			43,055
Retail Banking		1,144,964		8,760			282,614			1,062,923		9,198			219,234
All Other		751,703		(32,915	)		(11,587	)		595,204		(35,917	)		(53,607	)
Total	$	4,176,684		—			1,085,903		$	3,954,660		—			984,543

14. Segment information, continued

	Average Total Assets
	Nine Months Ended September 30				Year Ended December 31
	2017		2016		2016
	(In millions)

Business Banking	$	5,596		5,442		5,456
Commercial Banking		26,699		25,363		25,592
Commercial Real Estate		22,800		20,571		21,131
Discretionary Portfolio		37,807		41,253		40,867
Residential Mortgage Banking		2,335		2,578		2,569
Retail Banking		12,519		11,739		11,840
All Other		13,317		16,951		16,885
Total	$	121,073		123,897		124,340

(a)

Total revenues are comprised of net interest income and other income. Net interest income is the difference between taxable-equivalent interest earned on assets and interest paid on liabilities owed by a segment and a funding charge (credit) based on the Company's internal funds transfer and allocation methodology. Segments are charged a cost to fund any assets (e.g. loans) and are paid a funding credit for any funds provided (e.g. deposits). The taxable-equivalent adjustment aggregated $8,828,000 and $6,725,000 for the three-month periods ended September 30, 2017 and 2016, respectively, and $25,563,000 and $19,579,000 for the nine-month periods ended September 30, 2017 and 2016, respectively, and is eliminated in "All Other" total revenues. Intersegment revenues are included in total revenues of the reportable segments. The elimination of intersegment revenues is included in the determination of "All Other" total revenues.

Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P.	9 Months Ended
	Sep. 30, 2017
Text Block [Abstract]
Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P.	15. Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. M&T holds a 20% minority interest in Bayview Lending Group LLC ("BLG"), a privately-held commercial mortgage company. M&T recognizes income or loss from BLG using the equity method of accounting. That investment had no remaining carrying value at September 30, 2017 as a result of cumulative losses recognized and cash distributions received. Bayview Financial Holdings, L.P. (together with its affiliates, "Bayview Financial"), a privately-held specialty mortgage finance company, is BLG's majority investor. In addition to their common investment in BLG, the Company and Bayview Financial conduct other business activities with each other. The Company has obtained loan servicing rights for mortgage loans from BLG and Bayview Financial having outstanding principal balances of $3.2 billion and $3.5 billion at September 30, 2017 and December 31, 2016, respectively. Revenues from those servicing rights were $4 million and $5 million for the three-month periods ended September 30, 2017 and 2016, respectively, and $13 million and $15 million for the nine-month periods ended September 30, 2017 and 2016, respectively. The Company sub-services residential mortgage loans for Bayview Financial having outstanding principal balances of $59.3 billion and $30.4 billion at September 30, 2017 and December 31, 2016, respectively. Revenues earned for sub-servicing loans for Bayview Financial were $26 million and $25 million for the three-month periods ended September 30, 2017 and 2016, respectively, and $74 million and $73 million for the nine-month periods ended September 30, 2017 and 2016, respectively. In addition, the Company held $141 million and $158 million of mortgage-backed securities in its held-to-maturity portfolio at September 30, 2017 and December 31, 2016, respectively, that were securitized by Bayview Financial. In April 2017, the Company provided a loan to Bayview Financial for $100 million at terms consistent with those offered to non-affiliated customers. That loan was subsequently paid in full in June 2017. Also in June 2017, a new syndicated loan facility was entered into by Bayview Financial for $750 million, of which the Company held $88 million at September 30, 2017.

Recent accounting developments	9 Months Ended
Recent accounting developments	Sep. 30, 2017
Accounting Changes And Error Corrections [Abstract]
Recent accounting developments	16. Recent accounting developments Effective January 1, 2017, the Company adopted amended accounting guidance for share-based transactions. The most significant aspect of the amended guidance that affects the Company requires that all excess tax benefits and tax deficiencies be recognized in income tax expense in the income statement and that such amounts be recognized in the period in which the tax deduction arises or in the period in which an expiration of an award occurs. The adoption of this guidance resulted in an $18 million reduction of income tax expense for the three-month period ended March 31, 2017, that under previous accounting guidance would have been recognized directly in shareholders’ equity. The amended accounting guidance did not have a significant impact on income tax expense in the three-month periods ended September 30 and June 30, 2017. Effective January 2017, the Company also adopted amended accounting guidance for the transition to the equity method of accounting. The amended guidance eliminates the requirement that when an investment qualifies for use of the equity method as a result of an increase in the level of ownership interest or degree of influence, an investor must adjust the investment, results of operations, and retained earnings retroactively on a step-by-step basis as if the equity method has been in effect during all previous periods that the investment had been held. Instead, the amended guidance requires the investor to adopt the equity method of accounting as of the date the investment first qualifies for such accounting. The adoption of this guidance did not have a material effect on the Company’s consolidated financial position or results of operations. In January 2017, the Company adopted two amendments to the accounting guidance for derivatives and hedging. The first amendment clarifies that a change in the counterparty to a derivative instrument that has been designated as the hedging instrument does not, in and of itself, require dedesignation of that hedging relationship provided that all other hedge accounting criteria continue to be met. The second amendment clarifies the requirements for assessing whether contingent call (put) options that can accelerate the payment of principal on debt instruments are clearly and closely related to their debt hosts. An entity performing the assessment is required to assess the embedded call (put) options solely in accordance with a four-step decision sequence and no longer has to assess whether the event that triggers the ability to exercise the option is related to interest rates or credit risks. The adoption of this guidance did not have a material effect on the Company’s consolidated financial position or results of operations. In August 2017, the Financial Accounting Standards Board (“FASB”) issued amended guidance expanding and clarifying hedge accounting for nonfinancial and financial risk components, aligning the recognition and presentation of the effects of the hedging instrument and hedged item in the financial statements, and simplifying the requirements for assessing effectiveness in a hedging relationship. The guidance eliminates the concept of benchmark interest rates for cash flow hedges of interest rate risk and permits variability in cash flows attributable to the contractually specified interest rate to be designated as the hedged risk in a cash flows hedge of a variable-rate financial instrument. For a fair value hedge of interest rate risk, the amended guidance added the Securities Industry and Financial Markets Association Municipal Swap Rate as an eligible benchmark interest rate. The amendments also change the guidance for designating fair value hedges of interest rate risk and for measuring the change in fair value of the hedged item in fair value hedges of interest rate risk by (1) for a closed portfolio of prepayable financial assets or one or more beneficial interests secured by a portfolio of prepayable financial instruments, permitting an amount that is not expected to be affected by prepayments, defaults, and other events affecting the timing and amount of cash flow (“last of layer” method) to be designated as the hedged item, (2) permitting the change in fair value of the hedged item to be measured on the basis of the benchmark interest rate component of the contractual coupon cash flows rather than the full contractual coupon cash flows, (3) permitting the hedged item in a partial-term fair value hedge to be measured by assuming the hedged item has a term that reflects only the designated cash flows being hedged, and (4) for prepayable financial instruments, permitting the consideration of only how changes in the benchmark interest rate affect a decision to settle a debt instrument before its scheduled maturity in calculating the change in fair value of the hedged item attributable to interest rate risk. As it relates to aligning the recognition and 16. Recent accounting developments, continued presentation of the effects of the hedging instrument and hedged item in the financial statements, the amended guidance requires (1) the entire change in fair value of the hedging instrument that is included in the assessment of hedge effectiveness to be presented in the same income statement line item that is used to present the earnings effect of the hedged item in a fair value hedge and the hedged transaction in a cash flow hedge and (2) for cash flow hedges, the entire change in fair value of the hedging instrument to be included in other comprehensive income (hedge ineffectiveness no longer will be recognized in earnings for cash flow hedges) and reclassified to earnings when the hedged forecasted transaction effects earnings. From the perspective of simplifying the requirements for assessing effectiveness in a hedging relationship, the amendments permit (1) qualitative subsequent assessments of hedge effectiveness when the facts and circumstances related to the hedging relationship have not changed, (2) initial prospective quantitative assessments at any time after hedge designation up to the first quarterly effectiveness testing date, and (3) application of the long-haul method for assessing hedge effectiveness if the shortcut method was initially applied and is no longer appropriate. The guidance is effective for annual periods and interim periods within those annual periods beginning after December 15, 2018, with early adoption permitted. If adopted in an interim period, the effects of the adoption should be reflected as of the beginning of the fiscal year of adoption. For cash flow hedges existing at the date of adoption, a cumulative-effect adjustment should be applied related to eliminating the separate measurement of ineffectiveness to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year that an entity adopts the amendments. The amended presentation and disclosure guidance is required only prospectively. The Company is evaluating when it will adopt the amended guidance and does not expect such adoption will have a material impact on its consolidated financial statements. In May 2017, the FASB issued amended guidance relating to which changes to the terms and conditions of a share-based payment award require an entity to apply modification accounting. The guidance requires an entity to account for the effects of a modification unless all the following criteria are met: (1) the fair value of the modified award is the same as the fair value of the original award immediately before the original award was modified. If the modification does not affect any of the inputs to the valuation technique that the entity uses to value the award, the entity is not required to estimate the value immediately before and after the modification; (2) the vesting conditions of the modified award are the same as the vesting conditions of the original award immediately before the original award was modified; and (3) the classification of the modified award as an equity instrument or a liability instrument is the same as the classification of the original award immediately before the original award was modified. The guidance is effective for annual periods; and interim periods within those annual periods beginning after December 15, 2017, and should be applied on a prospective basis to an award modified on or after the adoption date. The Company does not expect the guidance to have a material impact on its consolidated financial statements. In March 2017, the FASB issued amended guidance requiring the premium on callable debt securities held at a premium to be amortized to the earliest call date. The amendments do not require an accounting change for securities held at a discount; the discount continues to be amortized to maturity. The guidance is effective for annual periods and interim periods within those annual periods beginning after December 15, 2018, with early adoption permitted. If adopted in an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. The amendments should be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. The Company does not expect the guidance to have a material impact on its consolidated financial statements. In March 2017, the FASB issued amended guidance requiring the service cost component of the net periodic pension cost and net periodic postretirement benefit cost to be reported in the same line item in the income statement as other compensation costs arising from services rendered by the pertinent employees during the period. The amendments also require that the other components of net benefit costs be presented separately from the service cost 16. Recent accounting developments, continued component. The guidance is effective for annual periods and interim periods within those annual periods beginning after December 15, 2017, using a retrospective transition method for the presentation of the service cost and other components of net periodic pension cost and net periodic postretirement benefit cost in the income statement. The amendments allow for a practical expedient that permits the use of the amounts disclosed in the Company’s pension and other postretirement benefit plan note for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. The Company does not expect the guidance to have a material impact on its consolidated financial statements. In January 2017, the FASB issued amended guidance eliminating step 2 from the goodwill impairment test. Under the amendments to the guidance, an entity should perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. The loss recognized, however, should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. The guidance is effective for annual periods or any interim goodwill impairment tests beginning after December 15, 2019 using a prospective transition method. Early adoption is permitted. The Company does not expect the guidance will have a material impact on its consolidated financial statements, unless at some point in the future one of its reporting units were to fail step 1 of the goodwill impairment test. In January 2017, the FASB issued amended guidance clarifying the definition of a business for purposes of evaluating whether transactions would be accounted for as acquisitions (or disposals) of assets or businesses. The amendments provide a screen to determine when a set of assets and activities (collectively referred to as a “set”) is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired (or disposed of) is concentrated in a single identifiable asset or group of similar assets, the set is not a business. If the screen is not met, the amendments (1) require that to be considered a business, a set must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create output, and (2) remove the evaluation of whether a market participant could replace missing elements. The guidance is effective for annual periods and interim periods within those annual periods beginning after December 15, 2017 using a prospective transition method. The Company does not expect the guidance to have a material impact on its consolidated financial statements. In November 2016, the FASB issued amended guidance for the presentation of restricted cash in the statement of cash flows. The guidance requires that restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. In addition, when cash, cash equivalents, and restricted cash or restricted cash equivalents are presented in more than one line item within the statement of financial position, the line items and amounts must be presented on the face of the statement of cash flows or disclosed in the notes to the financial statements. Information about the nature of restrictions on an entity’s cash and cash equivalents must also be disclosed. The guidance, which applies only to the consolidated statement of cash flows, is effective for annual periods and interim periods within those annual periods beginning after December 15, 2017, using a retrospective transition method. 16. Recent accounting developments, continued In August 2016, the FASB issued amended guidance for how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The guidance addresses the following eight specific cash flow issues: (1) cash payments for debt extinguishment costs should be classified as cash outflows for financing activities; (2) for zero-coupon debt instruments, the portion of the cash payment attributable to the accreted interest should be classified as a cash outflow for operating activities; (3) contingent consideration payments made after a business combination should be classified based on the timing of the payment; (4) cash proceeds received from the settlement of insurance claims should be classified on the basis of the related insurance coverage; (5) cash proceeds received from the settlement of corporate-owned and bank-owned life insurance policies should be classified as cash inflows from investing activities; (6) when the equity method is applied, an accounting policy election should be made to classify distributions received using either the cumulative earnings approach or the nature of the distribution approach; (7) cash receipts from payments on a transferor’s beneficial interests obtained in a securitization of financial assets should be classified as cash inflows from investing activities; and (8) the classification of cash receipts and payments that have aspects of more than one class of cash flows should be determined by applying specific guidance in GAAP. The guidance, which only impacts the presentation of the consolidated statement of cash flows, is effective for annual periods and interim periods within those annual periods beginning after December 15, 2017. In June 2016, the FASB issued amended guidance for the measurement of credit losses on certain financial assets. The amended guidance requires financial assets measured at amortized cost to be presented at the net amount expected to be collected. The allowance for credit losses will represent a valuation account that is deducted from the amortized cost basis of the financial assets to present their net carrying value at the amount expected to be collected. The income statement will reflect the measurement of credit losses for newly recognized financial assets as well as expected increases or decreases of expected credit losses that have taken place during the period. When determining the allowance, expected credit losses over the contractual term of the financial asset(s) (taking into account prepayments) will be estimated considering relevant information about past events, current conditions, and reasonable and supportable forecasts that affect the collectibility of the reported amount. The amended guidance also requires recording an allowance for credit losses for purchased financial assets with a more-than-insignificant amount of credit deterioration since origination. The initial allowance for these assets will be added to the purchase price at acquisition rather than being reported as an expense. Subsequent changes in the allowance will be recorded through the income statement as an expense adjustment. In addition, the amended guidance requires credit losses relating to available-for-sale debt securities to be recorded through an allowance for credit losses. The calculation of credit losses for available-for-sale securities will be similar to how it is determined under existing guidance. The guidance is effective for annual periods and interim periods within those annual periods beginning after December 15, 2019. The Company is assessing the new guidance to determine what modifications to existing credit estimation processes may be required. The Company expects that the new guidance will result in an increase in its allowance for credit losses as a result of considering credit losses over the expected life of its loan portfolios. Increases in the level of the allowance for credit losses will also reflect new requirements to include the nonaccretable principal difference on purchased credit impaired loans and estimated credit losses on investment securities classified as held-to-maturity, if any. The Company is still evaluating the extent of the increase to the allowance for credit losses and the impact to its financial statements. In February 2016, the FASB issued guidance related to the accounting for leases. The core principle of the guidance is that all leases create an asset and a liability for the lessee and, therefore, lease assets and lease liabilities should be recognized in the balance sheet. Lease assets will be recognized as a right-of-use asset and lease liabilities will be recognized as a liability to make lease payments. While the guidance requires all leases to be recognized in the balance sheet, there continues to be a differentiation between finance leases and operating leases for purposes of income statement recognition and cash flow statement presentation. For finance leases, interest on the lease liability 16. Recent accounting developments, continued and amortization of the right-of-use asset will be recognized separately in the statement of income. Repayments of principal on those lease liabilities will be classified within financing activities and payments of interest on the lease liability will be classified within operating activities in the statement of cash flows. For operating leases, a single lease cost is recognized in the statement of income and allocated over the lease term, generally on a straight-line basis. All cash payments are presented within operating activities in the statement of cash flows. The accounting applied by lessors is largely unchanged from existing GAAP, however, the guidance eliminates the accounting model for leveraged leases for leases that commence after the effective date of the guidance. The guidance is effective for annual periods beginning after December 15, 2018, including interim periods within those fiscal years. The Company occupies certain banking offices and uses certain equipment under noncancelable operating lease agreements, which currently are not reflected in its consolidated balance sheet. Upon adoption of the guidance, the Company expects to report increased assets and increased liabilities as a result of recognizing right-of-use assets and lease liabilities on its consolidated balance sheet. The Company was committed to $467 million of minimum lease payments under noncancelable operating lease agreements at December 31, 2016. The Company does not expect the new guidance will have a material impact to its consolidated statement of income. In January 2016, the FASB issued amended guidance related to recognition and measurement of financial assets and liabilities. The amended guidance requires that equity investments (excluding those accounted for under the equity method of accounting or those that result in consolidation of the investee) be measured at fair value with changes in fair value recognized in net income. An entity can elect to measure equity investments that do not have readily determinable fair values at cost less impairment, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer. The impairment assessment of equity investments without readily determinable fair values is simplified by requiring a qualitative assessment to identify impairment. When a qualitative assessment indicates impairment exists, an entity is required to measure the investment at fair value. The guidance eliminates the requirement for public business entities to disclose the method and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet. Further, the guidance requires public entities to use the exit price when measuring the fair value of financial instruments for disclosure purposes. The guidance also requires an entity to present separately in other comprehensive income, a change in the instrument-specific credit risk when the entity has elected to measure a liability at fair value in accordance with the fair value option. Separate presentation of financial assets and liabilities by measurement category and type of instrument on the balance sheet or accompanying notes to the financial statements is required. The guidance also clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity’s other deferred tax assets. This guidance is effective for annual periods and interim periods within those annual periods beginning after December 15, 2017. The Company does hold certain equity securities in its available-for-sale portfolio. Upon adoption of this guidance, fair value changes in such equity securities will be recognized in the consolidated statement of income as opposed to accumulated other comprehensive income where they are recognized under current accounting guidance. Although those securities have historically fluctuated in value, how those securities could change in value in the future is not predictable. In May 2014, the FASB issued amended accounting and disclosure guidance for revenue from contracts with customers. The core principle of the accounting guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve that core principle, an entity should apply the following steps: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; (5) recognize revenue when (or as) the entity satisfies a performance obligation. The guidance also specifies the accounting for some costs to obtain or fulfill a contract with a customer. The amended disclosure guidance requires sufficient information to enable users of financial statements to understand the nature, amount, 16. Recent accounting developments, continued timing, and uncertainty of revenue and cash flows arising from contracts with customers. The amended guidance is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. The guidance should be applied either retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying this guidance recognized at the date of initial application (the “modified retrospective approach”). The Company expects to adopt the revenue recognition guidance in the first quarter of 2018. A significant amount of the Company’s revenues are derived from net interest income on financial assets and liabilities, which are excluded from the scope of the amended guidance. With respect to noninterest income, the Company has identified revenue streams within the scope of the guidance and is in the final stages of its accounting analysis of the underlying contracts. The Company does not presently expect that changes in the timing of revenue recognition will be material to the amount of annual revenue recognized by the Company.

Significant accounting policies (Policies)	9 Months Ended
Significant accounting policies (Policies)	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Accounting	The consolidated financial statements of M&T Bank Corporation (“M&T”) and subsidiaries (“the Company”) were compiled in accordance with generally accepted accounting principles (“GAAP”) using the accounting policies set forth in note 1 of Notes to Financial Statements included in Form 10-K for the year ended December 31, 2016 (“2016 Annual Report”), except that effective January 2017 the Company adopted amended accounting guidance that is discussed in note 16 herein. The most significant of those changes related to the accounting for excess tax benefits or deficiencies associated with share-based compensation whereby beginning in 2017 those amounts are recognized in income tax expense. Previously, tax effects resulting from changes in M&T’s share price subsequent to the grant date were recorded through shareholders’ equity. The adoption of this new accounting guidance resulted in a reduction of income tax expense for the three months ended March 31, 2017 of $18 million, or $.12 of diluted earnings per common share. The impact on income tax expense and diluted earnings per common share in the second and third quarters of 2017 was not significant. In the opinion of management, all adjustments necessary for a fair statement have been made and were all of a normal recurring nature.

Acquisitions (Tables)

9 Months Ended

Sep. 30, 2017

Business Combinations [Abstract]

Summary of Merger-Related Expenses

A summary of merger-related expenses included in the consolidated statement of income follows:

	Nine Months Ended September 30, 2016
	(In thousands)

Salaries and employee benefits	$	5,334
Equipment and net occupancy		1,278
Outside data processing and software		1,067
Advertising and marketing		10,522
Printing, postage and supplies		1,482
Other costs of operations		16,072
Total	$	35,755

Investment securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Amortized Cost and Estimated Fair Value of Investment Securities

The amortized cost and estimated fair value of investment securities were as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In thousands)
September 30, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	2,017,901		25		10,809	$	2,007,117
Obligations of states and political subdivisions		2,621		59		2		2,678
Mortgage-backed securities:
Government issued or guaranteed		9,155,485		92,915		63,917		9,184,483
Privately issued		30		—		—		30
Other debt securities		136,769		2,739		10,978		128,530
Equity securities		57,009		37,427		450		93,986
		11,369,815		133,165		86,156		11,416,824
Investment securities held to maturity:
Obligations of states and political subdivisions		32,445		190		81		32,554
Mortgage-backed securities:
Government issued or guaranteed		3,063,164		41,849		7,147		3,097,866
Privately issued		141,430		1,753		30,734		112,449
Other debt securities		5,085		—		—		5,085
		3,242,124		43,792		37,962		3,247,954
Other securities		414,978		—		—		414,978
Total	$	15,026,917		176,957		124,118	$	15,079,756

December 31, 2016
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,912,110	386	9,952	$	1,902,544
Obligations of states and political subdivisions		3,570	77	6		3,641
Mortgage-backed securities:
Government issued or guaranteed		10,980,507	88,343	113,989		10,954,861
Privately issued		45	—	1		44
Other debt securities		134,105	1,407	16,996		118,516
Equity securities		307,964	45,073	571		352,466
		13,338,301	135,286	141,515		13,332,072
Investment securities held to maturity:
Obligations of states and political subdivisions		60,858	267	224		60,901
Mortgage-backed securities:
Government issued or guaranteed		2,233,173	37,498	7,374		2,263,297
Privately issued		157,704	897	37,120		121,481
Other debt securities		5,543	—	—		5,543
		2,457,278	38,662	44,718		2,451,222
Other securities		461,118	—	—		461,118
Total	$	16,256,697	173,948	186,233	$	16,244,412

Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity

At September 30, 2017, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:

	Amortized Cost		Estimated Fair Value
	(In thousands)
Debt securities available for sale:
Due in one year or less	$	393,453		392,506
Due after one year through five years		1,632,143		1,622,447
Due after five years through ten years		72,508		72,854
Due after ten years		59,187		50,518
		2,157,291		2,138,325
Mortgage-backed securities available for sale		9,155,515		9,184,513
	$	11,312,806		11,322,838
Debt securities held to maturity:
Due in one year or less	$	18,640		18,738
Due after one year through five years		13,612		13,619
Due after five years through ten years		193		197
Due after ten years		5,085		5,085
		37,530		37,639
Mortgage-backed securities held to maturity		3,204,594		3,210,315
	$	3,242,124		3,247,954

Investment Securities in Continuous Unrealized Loss Position

	Less Than 12 Months					12 Months or More
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(In thousands)
September 30, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,576,717		(8,002	)		373,852		(2,807	)
Obligations of states and political subdivisions		—		—			474		(2	)
Mortgage-backed securities:
Government issued or guaranteed		2,854,982		(32,123	)		1,298,054		(31,794	)
Other debt securities		1,500		(3	)		60,518		(10,975	)
Equity securities		18,185		(303	)		153		(147	)
		4,451,384		(40,431	)		1,733,051		(45,725	)

Investment securities held to maturity:
Obligations of states and political subdivisions		4,932		(31	)		7,093		(50	)
Mortgage-backed securities:
Government issued or guaranteed		638,863		(2,832	)		157,923		(4,315	)
Privately issued		—		—			53,631		(30,734	)
		643,795		(2,863	)		218,647		(35,099	)
Total	$	5,095,179		(43,294	)		1,951,698		(80,824	)

December 31, 2016
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,710,241		(9,950	)		2,295		(2	)
Obligations of states and political subdivisions		—		—			593		(6	)
Mortgage-backed securities:
Government issued or guaranteed		6,730,829		(113,374	)		81,003		(615	)
Privately issued		—		—			27		(1	)
Other debt securities		100		(1	)		85,400		(16,995	)
Equity securities		17,776		(422	)		151		(149	)
		8,458,946		(123,747	)		169,469		(17,768	)

Investment securities held to maturity:
Obligations of states and political subdivisions		17,988		(126	)		11,891		(98	)
Mortgage-backed securities:
Government issued or guaranteed		618,832		(6,842	)		17,481		(532	)
Privately issued		17,911		(1,222	)		57,016		(35,898	)
		654,731		(8,190	)		86,388		(36,528	)
Total	$	9,113,677		(131,937	)		255,857		(54,296	)

Loans and leases and the allowance for credit losses (Tables)

9 Months Ended

Sep. 30, 2017

Receivables [Abstract]

Summary of Current, Past Due and Nonaccrual Loans

A summary of current, past due and nonaccrual loans as of September 30, 2017 and December 31, 2016 follows:

	Current		30-89 Days Past Due		Accruing Loans Past Due 90 Days or More (a)		Accruing Loans Acquired at a Discount Past Due 90 days or More (b)		Purchased Impaired (c)		Nonaccrual		Total
	(In thousands)
September 30, 2017
Commercial, financial, leasing, etc.	$	21,486,942		48,159		3,710		369		75		203,996	$	21,743,251
Real estate:
Commercial		24,724,768		273,539		1,710		7,523		20,509		200,193		25,228,242
Residential builder and developer		1,604,095		26,182		—		4,413		10,717		2,416		1,647,823
Other commercial construction		5,952,636		51,132		1,220		—		13,972		19,263		6,038,223
Residential		15,868,656		458,066		249,983		10,025		307,529		236,363		17,130,622
Residential — limited documentation		2,829,667		88,814		—		—		114,141		101,918		3,134,540
Consumer:
Home equity lines and loans		5,275,572		34,878		772		9,856		—		75,584		5,396,662
Automobile		3,327,148		67,280		—		1		—		21,267		3,415,696
Other		4,120,712		33,070		3,893		24,038		—		8,362		4,190,075
Total	$	85,190,196		1,081,120		261,288		56,225		466,943		869,362	$	87,925,134

December 31, 2016
Commercial, financial, leasing, etc.	$	22,287,857		53,503		6,195		417		641		261,434	$	22,610,047
Real estate:
Commercial		25,076,684		183,531		7,054		12,870		31,404		176,201		25,487,744
Residential builder and developer		1,884,989		4,667		5		1,952		14,006		16,707		1,922,326
Other commercial construction		5,985,118		77,701		922		198		14,274		18,111		6,096,324
Residential		17,631,377		485,468		281,298		11,537		378,549		229,242		19,017,471
Residential — limited documentation		3,239,344		88,366		—		—		139,158		106,573		3,573,441
Consumer:
Home equity lines and loans		5,502,091		44,565		—		12,678		—		81,815		5,641,149
Automobile		2,869,232		56,158		—		1		—		18,674		2,944,065
Other		3,491,629		31,286		5,185		21,491		—		11,258		3,560,849
Total	$	87,968,321		1,025,245		300,659		61,144		578,032		920,015	$	90,853,416

(a)	Excludes loans acquired at a discount.

(b)	Loans acquired at a discount that were recorded at fair value at acquisition date. This category does not include purchased impaired loans that are presented separately.

(c)	Accruing loans acquired at a discount that were impaired at acquisition date and recorded at fair value.

Outstanding Principal Balance and Carrying Amount of Loans and Included in Consolidated Balance Sheet

	September 30,		December 31,
	2017		2016
	(In thousands)

Outstanding principal balance	$	1,584,126		2,311,699
Carrying amount:
Commercial, financial, leasing, etc.		42,878		59,928
Commercial real estate		308,426		456,820
Residential real estate		665,278		799,802
Consumer		127,919		487,721
	$	1,144,501		1,804,271

Summary of Changes in Accretable Yield for Acquired Loans

A summary of changes in the accretable yield for loans acquired at a discount for the three months and nine months ended September 30, 2017 and 2016 follows:


	Three Months Ended September 30
	2017						2016
	Purchased			Other			Purchased			Other
	Impaired			Acquired			Impaired			Acquired
	(In thousands)

Balance at beginning of period	$	133,532			163,099		$	162,023			245,195
Interest income		(10,815	)		(20,064	)		(12,784	)		(26,540	)
Reclassifications from nonaccretable balance		30,799			6,041			2,256			12,050
Other (a)		—			1,545			—			(818	)
Balance at end of period	$	153,516			150,621		$	151,495			229,887

	Nine Months Ended September 30
	2017						2016
	Purchased			Other			Purchased			Other
	Impaired			Acquired			Impaired			Acquired
	(In thousands)

Balance at beginning of period	$	154,233			201,153		$	184,618			296,434
Interest income		(32,546	)		(66,505	)		(40,906	)		(97,300	)
Reclassifications from nonaccretable balance		31,829			11,076			7,783			20,647
Other (a)		—			4,897			—			10,106
Balance at end of period	$	153,516			150,621		$	151,495			229,887

(a)	Other changes in expected cash flows including changes in interest rates and prepayment assumptions.

Changes in Allowance for Credit Losses

Changes in the allowance for credit losses for the three months ended September 30, 2017 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	339,314			366,229			66,006			158,559			78,117	$	1,008,225
Provision for credit losses		2,451			(7,699	)		1,267			33,886			95		30,000
Net charge-offs
Charge-offs		(9,714	)		(258	)		(4,206	)		(32,874	)		—		(47,052	)
Recoveries		4,423			5,895			2,028			9,807			—		22,153
Net (charge-offs) recoveries		(5,291	)		5,637			(2,178	)		(23,067	)		—		(24,899	)
Ending balance	$	336,474			364,167			65,095			169,378			78,212	$	1,013,326

Changes in the allowance for credit losses for the three months ended September 30, 2016 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	316,079			349,674			69,660			157,361			77,722	$	970,496
Provision for credit losses		26,222			9,963			(6,232	)		16,539			508		47,000
Net charge-offs
Charge-offs		(21,075	)		(1,564	)		(6,754	)		(29,882	)		—		(59,275	)
Recoveries		6,958			1,704			1,919			7,319			—		17,900
Net (charge-offs) recoveries		(14,117	)		140			(4,835	)		(22,563	)		—		(41,375	)
Ending balance	$	328,184			359,777			58,593			151,337			78,230	$	976,121

Changes in the allowance for credit losses for the nine months ended September 30, 2017 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	330,833			362,719			61,127			156,288			78,030	$	988,997
Provision for credit losses		44,642			1,201			14,067			76,908			182		137,000
Net charge-offs
Charge-offs		(51,318	)		(7,556	)		(16,364	)		(96,060	)		—		(171,298	)
Recoveries		12,317			7,803			6,265			32,242			—		58,627
Net (charge-offs) recoveries		(39,001	)		247			(10,099	)		(63,818	)		—		(112,671	)
Ending balance	$	336,474			364,167			65,095			169,378			78,212	$	1,013,326

Changes in the allowance for credit losses for the nine months ended September 30, 2016 were as follows:

	Commercial, Financial,			Real Estate
	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
	(In thousands)

Beginning balance	$	300,404			326,831			72,238			178,320			78,199	$	955,992
Provision for credit losses		39,667			29,799			(610	)		59,113			31		128,000
Net charge-offs
Charge-offs		(34,711	)		(3,569	)		(18,816	)		(107,761	)		—		(164,857	)
Recoveries		22,824			6,716			5,781			21,665			—		56,986
Net (charge-offs) recoveries		(11,887	)		3,147			(13,035	)		(86,096	)		—		(107,871	)
Ending balance	$	328,184			359,777			58,593			151,337			78,230	$	976,121

Impaired Loans and Leases

	September 30, 2017						December 31, 2016
	Recorded Investment		Unpaid Principal Balance		Related Allowance		Recorded Investment		Unpaid Principal Balance		Related Allowance
	(In thousands)
With an allowance recorded:
Commercial, financial, leasing, etc.	$	148,747		179,120		49,447		168,072		184,432		48,480
Real estate:
Commercial		73,144		81,244		10,200		71,862		86,666		11,620
Residential builder and developer		6,537		6,842		288		7,396		8,361		506
Other commercial construction		1,626		1,785		292		2,475		2,731		448
Residential		97,483		118,030		3,475		86,680		105,944		3,457
Residential — limited documentation		79,030		94,194		4,600		82,547		97,718		6,000
Consumer:
Home equity lines and loans		48,231		52,975		8,711		44,693		48,965		8,027
Automobile		14,225		16,743		3,011		16,982		18,272		3,740
Other		3,176		5,633		650		3,791		5,296		776
		472,199		556,566		80,674		484,498		558,385		83,054
With no related allowance recorded:
Commercial, financial, leasing, etc.		80,952		97,073		—		100,805		124,786		—
Real estate:
Commercial		148,733		158,815		—		113,276		121,846		—
Residential builder and developer		1,174		1,174		—		14,368		21,124		—
Other commercial construction		17,850		37,237		—		15,933		35,281		—
Residential		17,312		23,291		—		16,823		24,161		—
Residential — limited documentation		11,091		18,480		—		15,429		24,590		—
		277,112		336,070		—		276,634		351,788		—
Total:
Commercial, financial, leasing, etc.		229,699		276,193		49,447		268,877		309,218		48,480
Real estate:
Commercial		221,877		240,059		10,200		185,138		208,512		11,620
Residential builder and developer		7,711		8,016		288		21,764		29,485		506
Other commercial construction		19,476		39,022		292		18,408		38,012		448
Residential		114,795		141,321		3,475		103,503		130,105		3,457
Residential — limited documentation		90,121		112,674		4,600		97,976		122,308		6,000
Consumer:
Home equity lines and loans		48,231		52,975		8,711		44,693		48,965		8,027
Automobile		14,225		16,743		3,011		16,982		18,272		3,740
Other		3,176		5,633		650		3,791		5,296		776
Total	$	749,311		892,636		80,674		761,132		910,173		83,054

Interest Income Recognized on Impaired Loans

	Three Months Ended September 30, 2017						Three Months Ended September 30, 2016
			Interest Income Recognized						Interest Income Recognized
	Average Recorded Investment		Total		Cash Basis		Average Recorded Investment		Total		Cash Basis
	(In thousands)

Commercial, financial, leasing, etc.	$	224,526		391		391		262,796		744		744
Real estate:
Commercial		233,572		1,425		1,425		175,256		1,806		1,806
Residential builder and developer		8,550		895		895		26,996		405		405
Other commercial construction		16,578		25		25		21,500		190		190
Residential		113,892		1,903		905		96,961		1,572		570
Residential — limited documentation		91,974		1,624		569		101,877		1,501		378
Consumer:
Home equity lines and loans		47,831		419		99		41,740		368		112
Automobile		14,588		251		22		18,571		303		19
Other		3,269		80		2		4,077		72		11
Total	$	754,780		7,013		4,333		749,774		6,961		4,235

	Nine Months Ended September 30, 2017						Nine Months Ended September 30, 2016
			Interest Income Recognized						Interest Income Recognized
	Average Recorded Investment		Total		Cash Basis		Average Recorded Investment		Total		Cash Basis
	(In thousands)

Commercial, financial, leasing, etc.	$	242,410		1,674		1,674		283,783		7,055		7,055
Real estate:
Commercial		205,814		3,213		3,213		177,579		3,891		3,891
Residential builder and developer		14,551		1,791		1,791		30,832		488		488
Other commercial construction		15,474		958		958		19,774		563		563
Residential		108,741		5,004		2,285		97,229		4,778		2,591
Residential — limited documentation		94,680		4,573		1,292		104,382		4,580		1,648
Consumer:
Home equity lines and loans		46,829		1,240		290		33,998		937		295
Automobile		15,483		788		62		20,358		964		83
Other		3,430		227		8		10,987		371		74
Total	$	747,412		19,468		11,573		778,922		23,627		16,688

Summary of Loan Grades

The following table summarizes the loan grades applied to the various classes of the Company’s commercial loans and commercial real estate loans.

			Real Estate
	Commercial,				Residential		Other
	Financial,				Builder and		Commercial
	Leasing, etc.		Commercial		Developer		Construction
	(In thousands)
September 30, 2017
Pass	$	20,561,077		24,309,923		1,580,763		5,830,122
Criticized accrual		978,178		718,126		64,644		188,838
Criticized nonaccrual		203,996		200,193		2,416		19,263
Total	$	21,743,251		25,228,242		1,647,823		6,038,223
December 31, 2016
Pass	$	21,398,581		24,570,269		1,789,071		5,912,351
Criticized accrual		950,032		741,274		116,548		165,862
Criticized nonaccrual		261,434		176,201		16,707		18,111
Total	$	22,610,047		25,487,744		1,922,326		6,096,324

Allocation of Allowance for Credit Losses on Basis of Company's Impairment Methodology

The allocation of the allowance for credit losses summarized on the basis of the Company’s impairment methodology was as follows:

	Commercial, Financial,		Real Estate
	Leasing, etc.		Commercial		Residential		Consumer		Total
	(In thousands)
September 30, 2017
Individually evaluated for impairment	$	49,447		10,780		8,075		12,372	$	80,674
Collectively evaluated for impairment		287,027		353,387		47,674		157,006		845,094
Purchased impaired		—		—		9,346		—		9,346
Allocated	$	336,474		364,167		65,095		169,378		935,114
Unallocated										78,212
Total									$	1,013,326
December 31, 2016
Individually evaluated for impairment	$	48,480		12,500		9,457		12,543	$	82,980
Collectively evaluated for impairment		282,353		348,301		47,993		143,745		822,392
Purchased impaired		—		1,918		3,677		—		5,595
Allocated	$	330,833		362,719		61,127		156,288		910,967
Unallocated										78,030
Total									$	988,997

Recorded Investment in Loans and Leases on Basis of Company's Impairment Methodology

The recorded investment in loans and leases summarized on the basis of the Company’s impairment methodology was as follows:

	Commercial, Financial,		Real Estate
	Leasing, etc.		Commercial		Residential		Consumer		Total
	(In thousands)
September 30, 2017
Individually evaluated for impairment	$	229,699		249,064		204,916		65,632	$	749,311
Collectively evaluated for impairment		21,513,477		32,620,026		19,638,576		12,936,801		86,708,880
Purchased impaired		75		45,198		421,670		—		466,943
Total	$	21,743,251		32,914,288		20,265,162		13,002,433	$	87,925,134
December 31, 2016
Individually evaluated for impairment	$	268,877		224,630		201,479		65,466	$	760,452
Collectively evaluated for impairment		22,340,529		33,222,080		21,871,726		12,080,597		89,514,932
Purchased impaired		641		59,684		517,707		—		578,032
Total	$	22,610,047		33,506,394		22,590,912		12,146,063	$	90,853,416

Loan Modification Activities that were Considered Troubled Debt Restructurings

					Post-modification (a)
	Number		Pre- modification recorded investment		Principal Deferral		Other		Combination of Concession Types		Total
Three Months Ended September 30, 2017	(Dollars in thousands)

Commercial, financial, leasing, etc.		49	$	15,812	$	5,888	$	97	$	9,251	$	15,236
Real estate:
Commercial		17		5,861		1,420		868		3,450		5,738
Residential		34		5,123		3,033		—		2,716		5,749
Residential — limited documentation		4		515		383		—		167		550
Consumer:
Home equity lines and loans		25		2,154		461		—		1,776		2,237
Automobile		17		342		326		—		16		342
Other		1		5		5		—		—		5
Total		147	$	29,812	$	11,516	$	965	$	17,376	$	29,857

Three Months Ended September 30, 2016

Commercial, financial, leasing, etc.		43	$	69,486	$	40,183	$	—	$	19,802	$	59,985
Real estate:
Commercial		18		14,925		11,644		—		2,614		14,258
Residential		30		5,638		4,714		—		1,214		5,928
Residential — limited documentation		6		827		470		—		493		963
Consumer:
Home equity lines and loans		26		2,552		251		—		2,301		2,552
Automobile		10		186		186		—		—		186
Other		1		26		26		—		—		26
Total		134	$	93,640	$	57,474	$	—	$	26,424	$	83,898

					Post-modification (a)
	Number		Pre- modification recorded investment		Principal Deferral		Other		Combination of Concession Types		Total
Nine Months Ended September 30, 2017	(Dollars in thousands)

Commercial, financial, leasing, etc.		162	$	93,346	$	18,449	$	6,459	$	47,211	$	72,119
Real estate:
Commercial		67		38,608		16,193		868		21,332		38,393
Residential builder and developer		3		12,291		—		—		10,879		10,879
Other commercial construction		2		168		168		—		—		168
Residential		105		22,459		11,608		—		12,557		24,165
Residential — limited documentation		17		3,724		618		—		3,352		3,970
Consumer:
Home equity lines and loans		85		7,885		1,040		491		6,442		7,973
Automobile		59		1,160		1,089		—		71		1,160
Other		6		85		85		—		—		85
Total		506	$	179,726	$	49,250	$	7,818	$	101,844	$	158,912

Nine Months Ended September 30, 2016

Commercial, financial, leasing, etc.		112	$	148,204	$	98,561	$	—	$	39,971	$	138,532
Real estate:
Commercial		55		36,984		17,802		4,576		13,546		35,924
Residential builder and developer		3		23,905		22,958		—		—		22,958
Other commercial construction		2		374		250		—		124		374
Residential		73		11,946		7,945		—		4,705		12,650
Residential — limited documentation		14		2,415		803		—		1,872		2,675
Consumer:
Home equity lines and loans		84		9,189		655		—		8,534		9,189
Automobile		148		1,005		865		55		85		1,005
Other		78		1,192		951		45		196		1,192
Total		569	$	235,214	$	150,790	$	4,676	$	69,033	$	224,499

(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages. The present value of interest rate concessions, discounted at the effective rate of the original loan, was not material.

Shareholders' equity (Tables)

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Issued and Outstanding Preferred Stock

Issued and outstanding preferred stock of M&T as of September 30, 2017 and December 31, 2016 is presented below:

	Shares Issued and Outstanding		Carrying Value
	(Dollars in thousands)
Series A (a)
Fixed Rate Cumulative Perpetual Preferred Stock, $1,000 liquidation preference per share		230,000	$	230,000
Series C (a)
Fixed Rate Cumulative Perpetual Preferred Stock, $1,000 liquidation preference per share		151,500	$	151,500
Series E (b)
Fixed-to-Floating Rate Non-cumulative Perpetual Preferred Stock, $1,000 liquidation preference per share		350,000	$	350,000
Series F (c)
Fixed-to-Floating Rate Non-cumulative Perpetual Preferred Stock, $10,000 liquidation preference per share		50,000	$	500,000

(a)	Dividends, if declared, are paid at 6.375%. Warrants to purchase M&T common stock at $73.79 per share issued in connection with the Series A preferred stock expire in 2018 and totaled 327,358 at September 30, 2017.

(b)

(c)

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=65877616&loc=d3e177068-122764

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(d))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21553-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65888546&loc=d3e21300-112643

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21521-112644

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21484-112644

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21488-112644

+ Details

Pension plans and other postretirement benefits (Tables)

9 Months Ended

Sep. 30, 2017

Compensation And Retirement Disclosure [Abstract]

Net Periodic Defined Benefit Cost for Defined Benefit Plans

Net periodic defined benefit cost for defined benefit plans consisted of the following:

	Pension Benefits						Other Postretirement Benefits
	Three Months Ended September 30
	2017			2016			2017			2016
	(In thousands)

Service cost	$	5,048			6,259			293		399
Interest cost on projected benefit obligation		19,818			20,853			929			1,242
Expected return on plan assets		(27,131	)		(27,118	)		—			—
Amortization of prior service cost (credit)		139			(807	)		(340	)		(339	)
Amortization of net actuarial loss (gain)		7,316			7,536			(247	)		15
Net periodic benefit cost	$	5,190			6,723			635			1,317

	Pension Benefits						Other Postretirement Benefits
	Nine Months Ended September 30
	2017			2016			2017			2016
	(In thousands)

Service cost	$	15,145			18,778			878			1,197
Interest cost on projected benefit obligation		59,452			62,558			2,787			3,728
Expected return on plan assets		(81,393	)		(81,355	)		—			—
Amortization of prior service cost (credit)		418			(2,421	)		(1,019	)		(1,019	)
Amortization of net actuarial loss (gain)		21,947			22,609			(741	)		45
Net periodic benefit cost	$	15,569			20,169			1,905			3,951

Earnings per common share (Tables)

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Computations of Basic Earnings Per Common Share

The computations of basic earnings per common share follow:

	Three Months Ended September 30						Nine Months Ended September 30
	2017			2016			2017			2016
	(In thousands, except per share)
Income available to common shareholders:
Net income	$	355,923			349,984			1,085,903			984,543
Less: Preferred stock dividends (a)		(18,130	)		(20,318	)		(54,604	)		(60,953	)
Net income available to common equity		337,793			329,666			1,031,299			923,590
Less: Income attributable to unvested stock-based compensation awards		(1,992	)		(2,674	)		(6,288	)		(7,920	)
Net income available to common shareholders	$	335,801			326,992			1,025,011			915,670
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards		152,245			156,767			153,814			158,710
Less: Unvested stock-based compensation awards		(898	)		(1,274	)		(948	)		(1,374	)
Weighted-average shares outstanding		151,347			155,493			152,866			157,336

Basic earnings per common share	$	2.22			2.10			6.71			5.82

(a)Including impact of not as yet declared cumulative dividends.

Computations of Diluted Earnings Per Common Share

The computations of diluted earnings per common share follow:

	Three Months Ended September 30						Nine Months Ended September 30
	2017			2016			2017			2016
	(In thousands, except per share)

Net income available to common equity	$	337,793			329,666			1,031,299			923,590
Less: Income attributable to unvested stock-based compensation awards		(1,989	)		(2,668	)		(6,276	)		(7,904	)
Net income available to common shareholders	$	335,804			326,998			1,025,023			915,686
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards		152,245			156,767			153,814			158,710
Less: Unvested stock-based compensation awards		(898	)		(1,274	)		(948	)		(1,374	)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock		344			533			427			507
Adjusted weighted-average shares outstanding		151,691			156,026			153,293			157,843

Diluted earnings per common share	$	2.21			2.10			6.69			5.80

Comprehensive income (Tables)

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income

The following tables display the components of other comprehensive income (loss) and amounts reclassified from accumulated other comprehensive income (loss) to net income:

	Investment Securities						Defined Benefit						Total Amount				Income
	With OTTI (a)			All Other			Plans			Other			Before Tax				Tax			Net
	(In thousands)

Balance — January 1, 2017	$	46,725			(73,785	)		(449,917	)		(8,268	)	$	(485,245	)			190,609		$	(294,636	)
Other comprehensive income before reclassifications:
Unrealized holding gains (losses), net		(7,365	)		60,586			—			—			53,221				(20,934	)		32,287
Foreign currency translation adjustment		—			—			—			3,829			3,829				(1,340	)		2,489
Unrealized losses on cash flow hedges		—			—			—			(1,076	)		(1,076	)			424			(652	)
Total other comprehensive income (loss) before reclassifications		(7,365	)		60,586			—			2,753			55,974				(21,850	)		34,124
Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities		—			2,535			—			—			2,535		(b)		(998	)		1,537
(Gains) losses realized in net income		(50	)		67			—			—			17		(c)		(7	)		10
Accretion of net gain on terminated cash flow hedges		—			—			—			(109	)		(109	)	(d)		43			(66	)
Net yield adjustment from cash flow hedges currently in effect		—			—			—			(2,275	)		(2,275	)	(b)		895			(1,380	)
Amortization of prior service credit		—			—			(601	)		—			(601	)	(e)		236			(365	)
Amortization of actuarial losses		—			—			21,206			—			21,206		(e)		(8,345	)		12,861
Total reclassifications		(50	)		2,602			20,605			(2,384	)		20,773				(8,176	)		12,597
Total gain (loss) during the period		(7,415	)		63,188			20,605			369			76,747				(30,026	)		46,721
Balance — September 30, 2017	$	39,310			(10,597	)		(429,312	)		(7,899	)	$	(408,498	)			160,583		$	(247,915	)

Balance — January 1, 2016	$	16,359			62,849			(489,660	)		(4,093	)	$	(414,545	)			162,918		$	(251,627	)
Other comprehensive income before reclassifications:
Unrealized holding gains, net		1,228			234,438			—			—			235,666				(92,714	)		142,952
Foreign currency translation adjustment		—			—			—			(2,836	)		(2,836	)			989			(1,847	)
Total other comprehensive income (loss) before reclassifications		1,228			234,438			—			(2,836	)		232,830				(91,725	)		141,105
Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
Amortization of unrealized holding losses on HTM securities		—			2,998			—			—			2,998		(b)		(1,180	)		1,818
Gains realized in net income		—			(28,748	)		—			—			(28,748	)	(c)		11,309			(17,439	)
Accretion of net gain on terminated cash flow hedges		—			—			—			(116	)		(116	)	(d)		46			(70	)
Amortization of prior service credit		—			—			(3,440	)		—			(3,440	)	(e)		1,354			(2,086	)
Amortization of actuarial losses		—			—			22,654			—			22,654		(e)		(8,914	)		13,740
Total reclassifications		—			(25,750	)		19,214			(116	)		(6,652	)			2,615			(4,037	)
Total gain (loss) during the period		1,228			208,688			19,214			(2,952	)		226,178				(89,110	)		137,068
Balance — September 30, 2016	$	17,587			271,537			(470,446	)		(7,045	)	$	(188,367	)			73,808		$	(114,559	)

(a)	Other-than-temporary impairment

(b)	Included in interest income

(c)	Included in gain (loss) on bank investment securities

(d)	Included in interest expense

(e)	Included in salaries and employee benefits expense

Accumulated Other Comprehensive Income (Loss), Net

Accumulated other comprehensive income (loss), net consisted of the following:

	Investment Securities						Defined Benefit
	With OTTI			All Other			Plans			Other			Total
	(In thousands)

Balance — December 31, 2016	$	28,338			(44,657	)		(272,874	)		(5,443	)	$	(294,636	)
Net gain (loss) during period		(4,496	)		38,330			12,496			391			46,721
Balance — September 30, 2017	$	23,842			(6,327	)		(260,378	)		(5,052	)	$	(247,915	)

Derivative financial instruments (Tables)

9 Months Ended

Sep. 30, 2017

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Information about Interest Rate Swap Agreements

Information about interest rate swap agreements entered into for interest rate risk management purposes summarized by type of financial instrument the swap agreements were intended to hedge follows:

					Weighted- Average Rate
	Notional Amount		Average Maturity		Fixed			Variable			Estimated Fair Value Gain (a)
	(In thousands)		(In years)								(In thousands)
September 30, 2017
Fair value hedges:
Fixed rate long-term borrowings (b)	$	4,950,000		2.9		2.63	%		2.04	%	$	697
Cash flow hedges:
Variable rate commercial real estate loans (b)		2,000,000		1.6		1.46	%		1.24	%		—
Total	$	6,950,000		2.5							$	697
December 31, 2016
Fair value hedges:
Fixed rate long-term borrowings (b)	$	900,000		1.1		3.75	%		2.08	%	$	11,892

(a)

(b)	Under the terms of these agreements, the Company receives settlement amounts at a fixed rate and pays at a variable rate.

Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet

Information about the fair values of derivative instruments in the Company’s consolidated balance sheet and consolidated statement of income follows:

	Asset Derivatives				Liability Derivatives
	Fair Value				Fair Value
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
	(In thousands)
Derivatives designated and qualifying as hedging instruments
Fair value hedges:
Interest rate swap agreements (a)	$	2,048	$	11,892	$	1,351	$	—
Commitments to sell real estate loans (a)		1,667		33,189		1,551		1,347
Cash flow hedges:
Interest rate swap agreements (a)		—		—		—		—
		3,715		45,081		2,902		1,347
Derivatives not designated and qualifying as hedging instruments
Mortgage-related commitments to originate real estate loans for sale (a)		13,962		8,060		240		735
Commitments to sell real estate loans (a)		3,153		5,210		936		399
Trading:
Interest rate contracts (b)		104,178		228,810		103,825		167,737
Foreign exchange and other option and futures contracts (b)		6,823		7,908		5,905		6,639
		128,116		249,988		110,906		175,510
Total derivatives	$	131,831	$	295,069	$	113,808	$	176,857

(a)	Asset derivatives are reported in other assets and liability derivatives are reported in other liabilities.

(b)

10. Derivative financial instruments, continued

Information about Fair Values of Derivative Instruments in Consolidated Statement of Income

	Amount of Gain (Loss) Recognized
	Three Months Ended September 30, 2017					Three Months Ended September 30, 2016
	Derivative			Hedged Item		Derivative			Hedged Item
	(In thousands)
Derivatives in fair value hedging relationships
Interest rate swap agreements:
Fixed rate long-term borrowings (a)	$	(13,509	)		14,026	$	(12,588	)		12,587
Derivatives not designated as hedging instruments
Trading:
Interest rate contracts (b)	$	(418	)			$	4,822
Foreign exchange and other option and futures contracts (b)		1,362					1,746
Total	$	944				$	6,568

	Amount of Gain (Loss) Recognized
	Nine Months Ended September 30, 2017					Nine Months Ended September 30, 2016
	Derivative			Hedged Item		Derivative			Hedged Item
	(In thousands)
Derivatives in fair value hedging relationships
Interest rate swap agreements:
Fixed rate long-term borrowings (a)	$	(23,423	)		23,049	$	(22,832	)		21,603
Derivatives not designated as hedging instruments
Trading:
Interest rate contracts (b)	$	2,363				$	11,578
Foreign exchange and other option and futures contracts (b)		4,766					5,415
Total	$	7,129				$	16,993

(a)

Reported as other revenues from operations.

(b)

Reported as trading account and foreign exchange gains.

Fair value measurements (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis

The following tables present assets and liabilities at September 30, 2017 and December 31, 2016 measured at estimated fair value on a recurring basis:

	Fair Value Measurements		Level 1 (a)		Level 2 (a)		Level 3
	(In thousands)
September 30, 2017
Trading account assets	$	170,516		47,927		122,589		—
Investment securities available for sale:
U.S. Treasury and federal agencies		2,007,117		—		2,007,117		—
Obligations of states and political subdivisions		2,678		—		2,678		—
Mortgage-backed securities:
Government issued or guaranteed		9,184,483		—		9,184,483		—
Privately issued		30		—		—		30
Other debt securities		128,530		—		128,530		—
Equity securities		93,986		50,917		43,069		—
		11,416,824		50,917		11,365,877		30
Real estate loans held for sale		571,199		—		571,199		—
Other assets (b)		20,830		—		6,868		13,962
Total assets	$	12,179,369		98,844		12,066,533		13,992
Trading account liabilities	$	109,730		—		109,730		—
Other liabilities (b)		4,078		—		3,838		240
Total liabilities	$	113,808		—		113,568		240

December 31, 2016
Trading account assets	$	323,867		46,135		277,732		—
Investment securities available for sale:
U.S. Treasury and federal agencies		1,902,544		—		1,902,544		—
Obligations of states and political subdivisions		3,641		—		3,641		—
Mortgage-backed securities:
Government issued or guaranteed		10,954,861		—		10,954,861		—
Privately issued		44		—		—		44
Other debt securities		118,516		—		118,516		—
Equity securities		352,466		301,711		50,755		—
		13,332,072		301,711		13,030,317		44
Real estate loans held for sale		1,056,180		—		1,056,180		—
Other assets (b)		58,351		—		50,291		8,060
Total assets	$	14,770,470		347,846		14,414,520		8,104
Trading account liabilities	$	174,376		—		174,376		—
Other liabilities (b)		2,481		—		1,746		735
Total liabilities	$	176,857		—		176,122		735

(a)	There were no significant transfers between Level 1 and Level 2 of the fair value hierarchy during the nine months ended September 30, 2017 and the year ended December 31, 2016.

(b)	Comprised predominantly of interest rate swap agreements used for interest rate risk management (Level 2), commitments to sell real estate loans (Level 2) and commitments to originate real estate loans to be held for sale (Level 3).

Changes in Level 3 Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the three months ended September 30, 2017 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Other Assets and Other Liabilities
	(In thousands)

Balance — June 30, 2017	$	35			12,425
Total gains (losses) realized/unrealized:
Included in earnings		—			22,313		(b)
Settlements		(5	)		—
Transfers in and/or out of Level 3 (a)		—			(21,016	)	(d)
Balance — September 30, 2017	$	30			13,722
Changes in unrealized gains included in earnings related to assets still held at September 30, 2017	$	—			12,659		(b)

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the three months ended September 30, 2016 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Collateralized Debt Obligations				Other Assets and Other Liabilities
	(In thousands)

Balance — June 30, 2016	$	57			43,305				21,383
Total gains (losses) realized/unrealized:
Included in earnings		—			28,475				45,534		(b)
Included in other comprehensive income		—			(15,050	)	(c)		—
Sales		—			(56,730	)			—
Settlements		(6	)		—				—
Transfers in and/or out of Level 3 (a)		—			—				(37,117	)	(d)
Balance — September 30, 2016	$	51			—				29,800
Changes in unrealized gains included in earnings related to assets still held at September 30, 2016	$	—			—				27,663		(b)

12. Fair value measurements, continued

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the nine months ended September 30, 2017 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Other Assets and Other Liabilities
	(In thousands)

Balance — January 1, 2017	$	44			7,325
Total gains (losses) realized/unrealized:
Included in earnings		—			65,824		(b)
Settlements		(14	)		—
Transfers in and/or out of Level 3 (a)		—			(59,427	)	(d)
Balance — September 30, 2017	$	30		$	13,722
Changes in unrealized gains included in earnings related to assets still held at September 30, 2017	$	—		$	13,684		(b)

The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the nine months ended September 30, 2016 were as follows:

	Investment Securities Available for Sale
	Privately Issued Mortgage-Backed Securities			Collateralized Debt Obligations				Other Assets and Other Liabilities
				(In thousands)

Balance — January 1, 2016	$	74			47,393				9,879
Total gains (losses) realized/unrealized:
Included in earnings		—			28,475				104,862		(b)
Included in other comprehensive income		—			(18,268	)	(c)		—
Sales		—			(56,730	)			—
Settlements		(23	)		(870	)			—
Transfers in and/or out of Level 3 (a)		—			—				(84,941	)	(d)
Balance — September 30, 2016	$	51			—				29,800
Changes in unrealized gains included in earnings related to assets still held at September 30, 2016	$	—			—				29,288		(b)

(a)	The Company’s policy for transfers between fair value levels is to recognize the transfer as of the actual date of the event or change in circumstances that caused the transfer.

(b)	Reported as mortgage banking revenues in the consolidated statement of income and includes the fair value of commitment issuances and expirations.

(c)	Reported as net unrealized losses on investment securities in the consolidated statement of comprehensive income. The Company sold its collateralized debt obligations during the third and fourth quarters of 2016.

(d)	Transfers out of Level 3 consist of interest rate locks transferred to closed loans.

Quantitative Information Related to Significant Unobservable Inputs

Fair Value

Valuation

Technique

Unobservable

Inputs/Assumptions

Range

(Weighted-

Average)

(In thousands)

September 30, 2017

Recurring fair value measurements

Privately issued mortgage-backed

securities

Two independent pricing quotes

—

Net other assets (liabilities) (a)

13,722

Discounted cash flow

Commitment expirations

0%-80% (28%)

December 31, 2016

Recurring fair value measurements

Privately issued mortgage-backed

securities

Two independent pricing quotes

—

Net other assets (liabilities) (a)

7,325

Discounted cash flow

Commitment expirations

0%-77% (30%)

(a)	Other Level 3 assets (liabilities) consist of commitments to originate real estate loans.

Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities)

The carrying amounts and estimated fair value for financial instrument assets (liabilities) are presented in the following table:

	September 30, 2017
	Carrying Amount			Estimated Fair Value			Level 1		Level 2			Level 3
	(In thousands)
Financial assets:
Cash and cash equivalents	$	1,368,252			1,368,252			1,290,532		77,720			—
Interest-bearing deposits at banks		6,306,484			6,306,484			—		6,306,484			—
Trading account assets		170,516			170,516			47,927		122,589			—
Investment securities		15,073,926			15,079,756			50,917		14,916,360			112,479
Loans and leases:
Commercial loans and leases		21,743,251			21,409,984			—		—			21,409,984
Commercial real estate loans		32,914,288			32,507,319			—		223,659			32,283,660
Residential real estate loans		20,265,162			20,369,392			—		4,557,929			15,811,463
Consumer loans		13,002,433			12,935,924			—		—			12,935,924
Allowance for credit losses		(1,013,326	)		—			—		—			—
Loans and leases, net		86,911,808			87,222,619			—		4,781,588			82,441,031
Accrued interest receivable		325,982			325,982			—		325,982			—
Financial liabilities:
Noninterest-bearing deposits	$	(33,111,246	)		(33,111,246	)		—		(33,111,246	)		—
Savings and interest-checking deposits		(52,936,615	)		(52,936,615	)		—		(52,936,615	)		—
Time deposits		(7,233,518	)		(7,294,182	)		—		(7,294,182	)		—
Deposits at Cayman Islands office		(232,014	)		(232,014	)		—		(232,014	)		—
Short-term borrowings		(200,768	)		(200,768	)		—		(200,768	)		—
Long-term borrowings		(8,577,645	)		(8,630,195	)		—		(8,630,195	)		—
Accrued interest payable		(69,290	)		(69,290	)		—		(69,290	)		—
Trading account liabilities		(109,730	)		(109,730	)		—		(109,730	)		—
Other financial instruments:
Commitments to originate real estate loans for sale	$	13,722			13,722			—		—			13,722
Commitments to sell real estate loans		2,333			2,333			—		2,333			—
Other credit-related commitments		(119,938	)		(119,938	)		—		—			(119,938	)
Interest rate swap agreements used for interest rate risk management		697			697			—		697			—

	December 31, 2016
	Carrying Amount			Estimated Fair Value			Level 1		Level 2			Level 3
				(In thousands)
Financial assets:
Cash and cash equivalents	$	1,320,549			1,320,549			1,249,654		70,895		—
Interest-bearing deposits at banks		5,000,638			5,000,638			—		5,000,638		—
Trading account assets		323,867			323,867			46,135		277,732		—
Investment securities		16,250,468			16,244,412			301,711		15,821,176			121,525
Loans and leases:
Commercial loans and leases		22,610,047			22,239,428		—		—				22,239,428
Commercial real estate loans		33,506,394			33,129,428		—			642,590			32,486,838
Residential real estate loans		22,590,912			22,638,167		—			4,912,488			17,725,679
Consumer loans		12,146,063			12,061,590		—			—			12,061,590
Allowance for credit losses		(988,997	)		—		—			—			—
Loans and leases, net		89,864,419			90,068,613		—			5,555,078			84,513,535
Accrued interest receivable		308,805			308,805		—			308,805		—
Financial liabilities:
Noninterest-bearing deposits	$	(32,813,896	)		(32,813,896	)	—			(32,813,896	)	—
Savings and interest-checking deposits		(52,346,207	)		(52,346,207	)	—			(52,346,207	)	—
Time deposits		(10,131,846	)		(10,222,585	)	—			(10,222,585	)	—
Deposits at Cayman Islands office		(201,927	)		(201,927	)	—			(201,927	)	—
Short-term borrowings		(163,442	)		(163,442	)	—			(163,442	)	—
Long-term borrowings		(9,493,835	)		(9,473,844	)	—			(9,473,844	)	—
Accrued interest payable		(75,172	)		(75,172	)	—			(75,172	)	—
Trading account liabilities		(174,376	)		(174,376	)	—			(174,376	)	—
Other financial instruments:
Commitments to originate real estate loans for sale	$	7,325			7,325		—			—			7,325
Commitments to sell real estate loans		36,653			36,653		—			36,653		—
Other credit-related commitments		(136,295	)		(136,295	)	—			—			(136,295	)
Interest rate swap agreements used for interest rate risk management		11,892			11,892		—			11,892		—

Commitments and contingencies (Tables)

9 Months Ended

Sep. 30, 2017

Commitments And Contingencies Disclosure [Abstract]

Company's Significant Commitments

The following table presents the Company's significant commitments. Certain of these commitments are not included in the Company's consolidated balance sheet.

	September 30,		December 31,
	2017		2016
	(In thousands)
Commitments to extend credit
Home equity lines of credit	$	5,492,892		5,499,609
Commercial real estate loans to be sold		170,786		70,100
Other commercial real estate		5,749,428		6,451,709
Residential real estate loans to be sold		482,650		478,950
Other residential real estate		202,702		232,721
Commercial and other		12,677,838		12,298,473
Standby letters of credit		2,657,352		2,987,091
Commercial letters of credit		42,684		44,723
Financial guarantees and indemnification contracts		3,385,498		3,043,580
Commitments to sell real estate loans		1,052,472		1,489,237

Segment information (Tables)

9 Months Ended

Sep. 30, 2017

Segment Reporting [Abstract]

Summary of Reclassified Segment Information on Comparable Basis

14. Segment information, continued

financial information has been reclassified to provide segment information on a comparable basis, as noted in the following tables.

	Three Months Ended September 30, 2016
	Total Revenues as Previously Reported		Impact of Changes			Total Revenues as Reclassified		Net Income (Loss) as Previously Reported			Impact of Changes			Net Income (Loss) as Reclassified
	(In thousands)

Business Banking	$	116,513		4,388			120,901	$	21,422			2,602			24,024
Commercial Banking		268,683		(155	)		268,528		102,796			(92	)		102,704
Commercial Real Estate		205,562		—			205,562		90,065			—			90,065
Discretionary Portfolio		114,391		(8,806	)		105,585		50,773			(5,222	)		45,551
Residential Mortgage Banking		108,576		(11,901	)		96,675		22,924			(7,059	)		15,865
Retail Banking		353,016		8,848			361,864		69,506			5,247			74,753
All Other		182,949		7,626			190,575		(7,502	)		4,524			(2,978	)
Total	$	1,349,690		—			1,349,690	$	349,984			—			349,984

	Nine Months Ended September 30, 2016
	Total Revenues as Previously Reported		Impact of Changes			Total Revenues as Reclassified		Net Income (Loss) as Previously Reported			Impact of Changes			Net Income (Loss) as Reclassified
	(In thousands)

Business Banking	$	344,562		13,022			357,584	$	69,617			7,723			77,340
Commercial Banking		787,781		(423	)		787,358		309,515			(251	)		309,264
Commercial Real Estate		575,117		—			575,117		254,682			—			254,682
Discretionary Portfolio		324,195		(28,575	)		295,620		151,522			(16,947	)		134,575
Residential Mortgage Banking		309,393		(28,539	)		280,854		59,981			(16,926	)		43,055
Retail Banking		1,037,727		25,196			1,062,923		204,291			14,943			219,234
All Other		575,885		19,319			595,204		(65,065	)		11,458			(53,607	)
Total	$	3,954,660		—			3,954,660	$	984,543			—			984,543

Information about Company's Segments

14. Segment information, continued

Information about the Company's segments is presented in the following table:

	Three Months Ended September 30
	2017								2016
	Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)			Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)
	(In thousands)

Business Banking	$	130,501		919			31,408		$	120,901		1,086			24,024
Commercial Banking		267,822		840			109,797			268,528		950			102,704
Commercial Real Estate		212,014		401			97,295			205,562		463			90,065
Discretionary Portfolio		65,808		(12,346	)		31,515			105,585		(14,795	)		45,551
Residential Mortgage Banking		90,018		18,866			13,546			96,675		22,051			15,865
Retail Banking		392,542		2,668			96,329			361,864		3,052			74,753
All Other		257,858		(11,348	)		(23,967	)		190,575		(12,807	)		(2,978	)
Total	$	1,416,563		—			355,923		$	1,349,690		—			349,984

	Nine Months Ended September 30
	2017								2016
	Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)			Total Revenues(a)		Inter- segment Revenues			Net Income (Loss)
	(In thousands)

Business Banking	$	375,816		2,836			85,146		$	357,584		3,274			77,340
Commercial Banking		818,846		2,603			328,211			787,358		2,917			309,264
Commercial Real Estate		604,437		1,165			269,113			575,117		1,299			254,682
Discretionary Portfolio		216,798		(37,670	)		95,200			295,620		(43,726	)		134,575
Residential Mortgage Banking		264,120		55,221			37,206			280,854		62,955			43,055
Retail Banking		1,144,964		8,760			282,614			1,062,923		9,198			219,234
All Other		751,703		(32,915	)		(11,587	)		595,204		(35,917	)		(53,607	)
Total	$	4,176,684		—			1,085,903		$	3,954,660		—			984,543

14. Segment information, continued

	Average Total Assets
	Nine Months Ended September 30				Year Ended December 31
	2017		2016		2016
	(In millions)

Business Banking	$	5,596		5,442		5,456
Commercial Banking		26,699		25,363		25,592
Commercial Real Estate		22,800		20,571		21,131
Discretionary Portfolio		37,807		41,253		40,867
Residential Mortgage Banking		2,335		2,578		2,569
Retail Banking		12,519		11,739		11,840
All Other		13,317		16,951		16,885
Total	$	121,073		123,897		124,340

(a)

Significant Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Significant Accounting Policies [Line Items]
Diluted	$ 2.21		$ 2.10	$ 6.69	$ 5.80
Adoption of New Accounting Guidance [Member]
Significant Accounting Policies [Line Items]
Reduction of Income tax expense		$ (18)
Diluted		$ 0.12

Acquisitions - Summary of Merger-Related Expenses (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Summary of merger-related expenses
Salaries and employee benefits	$ 399,089,000	$ 399,786,000	$ 1,247,851,000	$ 1,230,246,000
Equipment and net occupancy	75,558,000	75,263,000	223,721,000	225,165,000
Outside data processing and software	45,761,000	42,878,000	134,637,000	128,402,000
Advertising and marketing	17,403,000	21,996,000	49,837,000	66,063,000
Printing, postage and supplies	8,732,000	8,972,000	27,397,000	30,865,000
Other costs of operations	227,705,000	165,251,000	558,579,000	488,063,000
Hudson City [Member]
Summary of merger-related expenses
Salaries and employee benefits				5,334,000
Equipment and net occupancy				1,278,000
Outside data processing and software				1,067,000
Advertising and marketing				10,522,000
Printing, postage and supplies				1,482,000
Other costs of operations				16,072,000
Total	$ 0	$ 0	$ 0	$ 35,755,000

Acquisitions - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Hudson City [Member]
Business Acquisition [Line Items]
Merger-related expenses	$ 0	$ 0	$ 0	$ 35,755,000

Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities available for sale, amortized cost	$ 11,369,815	$ 13,338,301
Investment securities available for sale, gross unrealized gains	133,165	135,286
Investment securities available for sale, gross unrealized losses	86,156	141,515
Investment securities available for sale, estimated fair value	11,416,824	13,332,072
Amortized cost for held to maturity	3,242,124	2,457,278
Gross unrealized gains for held to maturity	43,792	38,662
Gross unrealized losses for held to maturity	37,962	44,718
Estimated fair value for held to maturity	3,247,954	2,451,222
Other securities, Amortized cost	414,978	461,118
Other securities, Estimated fair value	414,978	461,118
Total Amortized cost	15,026,917	16,256,697
Total gross unrealized gains	176,957	173,948
Total gross unrealized losses	124,118	186,233
Total estimated fair value	15,079,756	16,244,412
U.S. Treasury and Federal Agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities available for sale, amortized cost	2,017,901	1,912,110
Investment securities available for sale, gross unrealized gains	25	386
Investment securities available for sale, gross unrealized losses	10,809	9,952
Investment securities available for sale, estimated fair value	2,007,117	1,902,544
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities available for sale, amortized cost	2,621	3,570
Investment securities available for sale, gross unrealized gains	59	77
Investment securities available for sale, gross unrealized losses	2	6
Investment securities available for sale, estimated fair value	2,678	3,641
Amortized cost for held to maturity	32,445	60,858
Gross unrealized gains for held to maturity	190	267
Gross unrealized losses for held to maturity	81	224
Estimated fair value for held to maturity	32,554	60,901
Government Issued or Guaranteed [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities available for sale, amortized cost	9,155,485	10,980,507
Investment securities available for sale, gross unrealized gains	92,915	88,343
Investment securities available for sale, gross unrealized losses	63,917	113,989
Investment securities available for sale, estimated fair value	9,184,483	10,954,861
Amortized cost for held to maturity	3,063,164	2,233,173
Gross unrealized gains for held to maturity	41,849	37,498
Gross unrealized losses for held to maturity	7,147	7,374
Estimated fair value for held to maturity	3,097,866	2,263,297
Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities available for sale, amortized cost	30	45
Investment securities available for sale, gross unrealized losses		1
Investment securities available for sale, estimated fair value	30	44
Amortized cost for held to maturity	141,430	157,704
Gross unrealized gains for held to maturity	1,753	897
Gross unrealized losses for held to maturity	30,734	37,120
Estimated fair value for held to maturity	112,449	121,481
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities available for sale, amortized cost	136,769	134,105
Investment securities available for sale, gross unrealized gains	2,739	1,407
Investment securities available for sale, gross unrealized losses	10,978	16,996
Investment securities available for sale, estimated fair value	128,530	118,516
Amortized cost for held to maturity	5,085	5,543
Estimated fair value for held to maturity	5,085	5,543
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities available for sale, amortized cost	57,009	307,964
Investment securities available for sale, gross unrealized gains	37,427	45,073
Investment securities available for sale, gross unrealized losses	450	571
Investment securities available for sale, estimated fair value	$ 93,986	$ 352,466

Investment Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
Investment Securities - Additional Information (Detail)	Sep. 30, 2017 USD ($) Investment	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Investment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Investment Holdings [Line Items]
Gross realized gains on sale of investment securities	$ 0	$ 0	$ 0	$ 0
Number of investment securities with aggregate gross unrealized losses \| Investment	939		939
Unrealized losses on individual investment securities	$ 124,118,000		$ 124,118,000		$ 186,233,000
Cost method investment securities	$ 415,000,000		$ 415,000,000
Collateralized Debt Obligations [Member]
Investment Holdings [Line Items]
Net gain on securities sold		$ 28,000,000

Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Debt securities available for sale:
Due in one year or less	$ 393,453
Due after one year through five years	1,632,143
Due after five years through ten years	72,508
Due after ten years	59,187
Total available for sale (amortized cost)	2,157,291
Mortgage-backed securities available for sale	9,155,515
Total	11,312,806
Debt securities held to maturity:
Due in one year or less	18,640
Due after one year through five years	13,612
Due after five years through ten years	193
Due after ten years	5,085
Total available for held to maturity (amortized cost)	37,530
Mortgage-backed securities held to maturity	3,204,594
Amortized cost for held to maturity	3,242,124	$ 2,457,278
Debt securities available for sale:
Due in one year or less	392,506
Due after one year through five years	1,622,447
Due after five years through ten years	72,854
Due after ten years	50,518
Total available for sale (fair value)	2,138,325
Mortgage-backed securities available for sale	9,184,513
Total	11,322,838
Debt securities held to maturity:
Due in one year or less	18,738
Due after one year through five years	13,619
Due after five years through ten years	197
Due after ten years	5,085
Total available for held to maturity (fair value)	37,639
Mortgage-backed securities held to maturity	3,210,315
Total	$ 3,247,954	$ 2,451,222

Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	$ 4,451,384	$ 8,458,946
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(40,431)	(123,747)
Estimated fair value, 12 months or more	1,733,051	169,469
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(45,725)	(17,768)
Held to maturity, Estimated fair value, Less than 12 months	643,795	654,731
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(2,863)	(8,190)
Held to maturity, Estimated fair value, 12 months or more	218,647	86,388
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(35,099)	(36,528)
Total investment securities, fair value less than 12 months	5,095,179	9,113,677
Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses	(43,294)	(131,937)
Total of investment securities, fair value, 12 Months or More	1,951,698	255,857
Investment Securities Continuous Unrealized Loss Position Twelve Months or Longer Aggregate Losses	(80,824)	(54,296)
U.S. Treasury and Federal Agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	1,576,717	1,710,241
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(8,002)	(9,950)
Estimated fair value, 12 months or more	373,852	2,295
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(2,807)	(2)
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, 12 months or more	474	593
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(2)	(6)
Held to maturity, Estimated fair value, Less than 12 months	4,932	17,988
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(31)	(126)
Held to maturity, Estimated fair value, 12 months or more	7,093	11,891
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(50)	(98)
Government Issued or Guaranteed [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	2,854,982	6,730,829
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(32,123)	(113,374)
Estimated fair value, 12 months or more	1,298,054	81,003
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(31,794)	(615)
Held to maturity, Estimated fair value, Less than 12 months	638,863	618,832
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(2,832)	(6,842)
Held to maturity, Estimated fair value, 12 months or more	157,923	17,481
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(4,315)	(532)
Privately Issued Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, 12 months or more		27
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses		(1)
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	1,500	100
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(3)	(1)
Estimated fair value, 12 months or more	60,518	85,400
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(10,975)	(16,995)
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	18,185	17,776
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(303)	(422)
Estimated fair value, 12 months or more	153	151
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(147)	(149)
Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Held to maturity, Estimated fair value, Less than 12 months		17,911
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses		(1,222)
Held to maturity, Estimated fair value, 12 months or more	53,631	57,016
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	$ (30,734)	$ (35,898)

Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 85,190,196	$ 87,968,321
30-89 Days Past Due	1,081,120	1,025,245
Accruing Loans Past Due 90 Days or More	261,288	300,659
Purchased Impaired	466,943	578,032
Nonaccrual	869,362	920,015
Loans and leases, net of unearned discount	87,925,134	90,853,416
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	56,225	61,144
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,486,942	22,287,857
30-89 Days Past Due	48,159	53,503
Accruing Loans Past Due 90 Days or More	3,710	6,195
Purchased Impaired	75	641
Nonaccrual	203,996	261,434
Loans and leases, net of unearned discount	21,743,251	22,610,047
Commercial, Financial, Leasing, etc. [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	369	417
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	24,724,768	25,076,684
30-89 Days Past Due	273,539	183,531
Accruing Loans Past Due 90 Days or More	1,710	7,054
Purchased Impaired	20,509	31,404
Nonaccrual	200,193	176,201
Loans and leases, net of unearned discount	25,228,242	25,487,744
Commercial [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	7,523	12,870
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,604,095	1,884,989
30-89 Days Past Due	26,182	4,667
Accruing Loans Past Due 90 Days or More		5
Purchased Impaired	10,717	14,006
Nonaccrual	2,416	16,707
Loans and leases, net of unearned discount	1,647,823	1,922,326
Residential Builder and Developer [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	4,413	1,952
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,952,636	5,985,118
30-89 Days Past Due	51,132	77,701
Accruing Loans Past Due 90 Days or More	1,220	922
Purchased Impaired	13,972	14,274
Nonaccrual	19,263	18,111
Loans and leases, net of unearned discount	6,038,223	6,096,324
Other Commercial Construction [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More		198
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	15,868,656	17,631,377
30-89 Days Past Due	458,066	485,468
Accruing Loans Past Due 90 Days or More	249,983	281,298
Purchased Impaired	307,529	378,549
Nonaccrual	236,363	229,242
Loans and leases, net of unearned discount	17,130,622	19,017,471
Residential [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	10,025	11,537
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,829,667	3,239,344
30-89 Days Past Due	88,814	88,366
Purchased Impaired	114,141	139,158
Nonaccrual	101,918	106,573
Loans and leases, net of unearned discount	3,134,540	3,573,441
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,275,572	5,502,091
30-89 Days Past Due	34,878	44,565
Accruing Loans Past Due 90 Days or More	772
Nonaccrual	75,584	81,815
Loans and leases, net of unearned discount	5,396,662	5,641,149
Home Equity Lines and Loans [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	9,856	12,678
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,327,148	2,869,232
30-89 Days Past Due	67,280	56,158
Nonaccrual	21,267	18,674
Loans and leases, net of unearned discount	3,415,696	2,944,065
Automobile [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	1	1
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,120,712	3,491,629
30-89 Days Past Due	33,070	31,286
Accruing Loans Past Due 90 Days or More	3,893	5,185
Nonaccrual	8,362	11,258
Loans and leases, net of unearned discount	4,190,075	3,560,849
Other [Member] \| Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	$ 24,038	$ 21,491

Loans and Leases and the Allowance for Credit Losses - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Loans And Leases Receivable [Line Items]
Commercial real estate loans held for sale	$ 224	$ 643
Contractual principal and interest payments	$ 467	578
Loan delinquent period	90 days
Minimum delinquency period for loan level collectability analysis consumer mortgage	150 days
Amount of foreclosed residential real estate property held	$ 106	129
Loans secured by residential real estate that were in the process of foreclosure	$ 545	506
Percentage loans in the process of foreclosure, serviced by other entities, classified as purchased impaired	48.00%
Percentage loans in the process of foreclosure, serviced by other entities, classified as government guaranteed	20.00%
Residential Mortgage Loans [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	$ 347	414
Carrying value of loans for which partial charge-off has been recognized	39	44
Mortgage loans on real real estate not requiring charge off due to collateral carrying amount	19	16
Home Equity Loans and Lines of Credit [Member]
Loans And Leases Receivable [Line Items]
Carrying value of loans for which partial charge-off has been recognized	27	32
Mortgage loans on real real estate not requiring charge off due to collateral carrying amount	$ 33	$ 39
Maximum [Member]
Loans And Leases Receivable [Line Items]
Purchased impaired loans as a percentage of total assets	1.00%	1.00%

Loans and Leases and the Allowance for Credit Losses - Outstanding Principal Balance and Carrying Amount of Loans and Included in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$ 1,584,126	$ 2,311,699
Carrying amount	1,144,501	1,804,271
Commercial, Financial, Leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	42,878	59,928
Commercial Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	308,426	456,820
Residential Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	665,278	799,802
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$ 127,919	$ 487,721

Loans and Leases and the Allowance for Credit Losses - Summary of Changes in Accretable Yield for Acquired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 133,532	$ 162,023	$ 154,233	$ 184,618
Interest income	(10,815)	(12,784)	(32,546)	(40,906)
Reclassifications from nonaccretable balance	30,799	2,256	31,829	7,783
Balance at end of period	153,516	151,495	153,516	151,495
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	163,099	245,195	201,153	296,434
Interest income	(20,064)	(26,540)	(66,505)	(97,300)
Reclassifications from nonaccretable balance	6,041	12,050	11,076	20,647
Other	1,545	(818)	4,897	10,106
Balance at end of period	$ 150,621	$ 229,887	$ 150,621	$ 229,887

Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,008,225	$ 970,496	$ 988,997	$ 955,992
Provision for credit losses	30,000	47,000	137,000	128,000
Net charge-offs
Charge-offs	(47,052)	(59,275)	(171,298)	(164,857)
Recoveries	22,153	17,900	58,627	56,986
Net (charge-offs) recoveries	(24,899)	(41,375)	(112,671)	(107,871)
Ending balance	1,013,326	976,121	1,013,326	976,121
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	339,314	316,079	330,833	300,404
Provision for credit losses	2,451	26,222	44,642	39,667
Net charge-offs
Charge-offs	(9,714)	(21,075)	(51,318)	(34,711)
Recoveries	4,423	6,958	12,317	22,824
Net (charge-offs) recoveries	(5,291)	(14,117)	(39,001)	(11,887)
Ending balance	336,474	328,184	336,474	328,184
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	366,229	349,674	362,719	326,831
Provision for credit losses	(7,699)	9,963	1,201	29,799
Net charge-offs
Charge-offs	(258)	(1,564)	(7,556)	(3,569)
Recoveries	5,895	1,704	7,803	6,716
Net (charge-offs) recoveries	5,637	140	247	3,147
Ending balance	364,167	359,777	364,167	359,777
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	66,006	69,660	61,127	72,238
Provision for credit losses	1,267	(6,232)	14,067	(610)
Net charge-offs
Charge-offs	(4,206)	(6,754)	(16,364)	(18,816)
Recoveries	2,028	1,919	6,265	5,781
Net (charge-offs) recoveries	(2,178)	(4,835)	(10,099)	(13,035)
Ending balance	65,095	58,593	65,095	58,593
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	158,559	157,361	156,288	178,320
Provision for credit losses	33,886	16,539	76,908	59,113
Net charge-offs
Charge-offs	(32,874)	(29,882)	(96,060)	(107,761)
Recoveries	9,807	7,319	32,242	21,665
Net (charge-offs) recoveries	(23,067)	(22,563)	(63,818)	(86,096)
Ending balance	169,378	151,337	169,378	151,337
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,117	77,722	78,030	78,199
Provision for credit losses	95	508	182	31
Net charge-offs
Ending balance	$ 78,212	$ 78,230	$ 78,212	$ 78,230

Loans and Leases and the Allowance for Credit Losses - Impaired Loans and Leases (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	$ 472,199	$ 484,498
Unpaid principal balance with related allowance	556,566	558,385
Related allowance	80,674	83,054
Recorded investment with no related allowance	277,112	276,634
Unpaid principal balance with no related allowance	336,070	351,788
Recorded investment	749,311	761,132
Unpaid principal balance	892,636	910,173
Commercial Real Estate [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	73,144	71,862
Unpaid principal balance with related allowance	81,244	86,666
Related allowance	10,200	11,620
Recorded investment with no related allowance	148,733	113,276
Unpaid principal balance with no related allowance	158,815	121,846
Recorded investment	221,877	185,138
Unpaid principal balance	240,059	208,512
Automobile [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	14,225	16,982
Unpaid principal balance with related allowance	16,743	18,272
Related allowance	3,011	3,740
Recorded investment	14,225	16,982
Unpaid principal balance	16,743	18,272
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	148,747	168,072
Unpaid principal balance with related allowance	179,120	184,432
Related allowance	49,447	48,480
Recorded investment with no related allowance	80,952	100,805
Unpaid principal balance with no related allowance	97,073	124,786
Recorded investment	229,699	268,877
Unpaid principal balance	276,193	309,218
Residential Builder and Developer [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	6,537	7,396
Unpaid principal balance with related allowance	6,842	8,361
Related allowance	288	506
Recorded investment with no related allowance	1,174	14,368
Unpaid principal balance with no related allowance	1,174	21,124
Recorded investment	7,711	21,764
Unpaid principal balance	8,016	29,485
Other Commercial Construction [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	1,626	2,475
Unpaid principal balance with related allowance	1,785	2,731
Related allowance	292	448
Recorded investment with no related allowance	17,850	15,933
Unpaid principal balance with no related allowance	37,237	35,281
Recorded investment	19,476	18,408
Unpaid principal balance	39,022	38,012
Residential [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	97,483	86,680
Unpaid principal balance with related allowance	118,030	105,944
Related allowance	3,475	3,457
Recorded investment with no related allowance	17,312	16,823
Unpaid principal balance with no related allowance	23,291	24,161
Recorded investment	114,795	103,503
Unpaid principal balance	141,321	130,105
Residential Limited Documentation [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	79,030	82,547
Unpaid principal balance with related allowance	94,194	97,718
Related allowance	4,600	6,000
Recorded investment with no related allowance	11,091	15,429
Unpaid principal balance with no related allowance	18,480	24,590
Recorded investment	90,121	97,976
Unpaid principal balance	112,674	122,308
Home Equity Lines and Loans [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	48,231	44,693
Unpaid principal balance with related allowance	52,975	48,965
Related allowance	8,711	8,027
Recorded investment	48,231	44,693
Unpaid principal balance	52,975	48,965
Other [Member]
Financing Receivable Impaired [Line Items]
Recorded investment with related allowance	3,176	3,791
Unpaid principal balance with related allowance	5,633	5,296
Related allowance	650	776
Recorded investment	3,176	3,791
Unpaid principal balance	$ 5,633	$ 5,296

Loans and Leases and the Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	$ 754,780	$ 749,774	$ 747,412	$ 778,922
Interest Income Recognized, Total	7,013	6,961	19,468	23,627
Interest Income Recognized, Cash Basis	4,333	4,235	11,573	16,688
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	233,572	175,256	205,814	177,579
Interest Income Recognized, Total	1,425	1,806	3,213	3,891
Interest Income Recognized, Cash Basis	1,425	1,806	3,213	3,891
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	224,526	262,796	242,410	283,783
Interest Income Recognized, Total	391	744	1,674	7,055
Interest Income Recognized, Cash Basis	391	744	1,674	7,055
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	8,550	26,996	14,551	30,832
Interest Income Recognized, Total	895	405	1,791	488
Interest Income Recognized, Cash Basis	895	405	1,791	488
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	16,578	21,500	15,474	19,774
Interest Income Recognized, Total	25	190	958	563
Interest Income Recognized, Cash Basis	25	190	958	563
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	113,892	96,961	108,741	97,229
Interest Income Recognized, Total	1,903	1,572	5,004	4,778
Interest Income Recognized, Cash Basis	905	570	2,285	2,591
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	91,974	101,877	94,680	104,382
Interest Income Recognized, Total	1,624	1,501	4,573	4,580
Interest Income Recognized, Cash Basis	569	378	1,292	1,648
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	47,831	41,740	46,829	33,998
Interest Income Recognized, Total	419	368	1,240	937
Interest Income Recognized, Cash Basis	99	112	290	295
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	14,588	18,571	15,483	20,358
Interest Income Recognized, Total	251	303	788	964
Interest Income Recognized, Cash Basis	22	19	62	83
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	3,269	4,077	3,430	10,987
Interest Income Recognized, Total	80	72	227	371
Interest Income Recognized, Cash Basis	$ 2	$ 11	$ 8	$ 74

Loans and Leases and the Allowance for Credit Losses - Summary of Loan Grades (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 87,925,134	$ 90,853,416
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,743,251	22,610,047
Commercial, Financial, Leasing, etc. [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,561,077	21,398,581
Commercial, Financial, Leasing, etc. [Member] \| Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	978,178	950,032
Commercial, Financial, Leasing, etc. [Member] \| Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	203,996	261,434
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	25,228,242	25,487,744
Commercial [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	24,309,923	24,570,269
Commercial [Member] \| Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	718,126	741,274
Commercial [Member] \| Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	200,193	176,201
Residential Builder and Developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,647,823	1,922,326
Residential Builder and Developer [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,580,763	1,789,071
Residential Builder and Developer [Member] \| Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	64,644	116,548
Residential Builder and Developer [Member] \| Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,416	16,707
Other Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	6,038,223	6,096,324
Other Commercial Construction [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	5,830,122	5,912,351
Other Commercial Construction [Member] \| Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	188,838	165,862
Other Commercial Construction [Member] \| Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 19,263	$ 18,111

Loans and Leases and the Allowance for Credit Losses - Allocation of Allowance for Credit Losses on Basis of Company's Impairment Methodology (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	$ 80,674		$ 82,980
Allowance for credit losses	845,094		822,392
Allowance for credit losses	1,013,326	$ 1,008,225	988,997	$ 976,121	$ 970,496	$ 955,992
Purchased Impaired [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	9,346		5,595
Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	935,114		910,967
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	78,212	$ 78,117	78,030	$ 78,230	$ 77,722	$ 78,199
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	49,447		48,480
Allowance for credit losses	287,027		282,353
Commercial, Financial, Leasing, etc. [Member] \| Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	336,474		330,833
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	10,780		12,500
Allowance for credit losses	353,387		348,301
Commercial Real Estate [Member] \| Purchased Impaired [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses			1,918
Commercial Real Estate [Member] \| Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	364,167		362,719
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	8,075		9,457
Allowance for credit losses	47,674		47,993
Residential Real Estate [Member] \| Purchased Impaired [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	9,346		3,677
Residential Real Estate [Member] \| Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	65,095		61,127
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	12,372		12,543
Allowance for credit losses	157,006		143,745
Consumer Loans [Member] \| Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	$ 169,378		$ 156,288

Loans and Leases and the Allowance for Credit Losses - Recorded Investment in Loans and Leases on Basis of Company's Impairment Methodology (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Recorded investment in loans and leases, individually evaluated for impairment	$ 749,311	$ 760,452
Recorded investment in loans and leases, collectively evaluated for impairment	86,708,880	89,514,932
Recorded investment in loans and leases, purchased impaired	466,943	578,032
Loans and leases, net of unearned discount	87,925,134	90,853,416
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment in loans and leases, individually evaluated for impairment	229,699	268,877
Recorded investment in loans and leases, collectively evaluated for impairment	21,513,477	22,340,529
Recorded investment in loans and leases, purchased impaired	75	641
Loans and leases, net of unearned discount	21,743,251	22,610,047
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment in loans and leases, individually evaluated for impairment	249,064	224,630
Recorded investment in loans and leases, collectively evaluated for impairment	32,620,026	33,222,080
Recorded investment in loans and leases, purchased impaired	45,198	59,684
Loans and leases, net of unearned discount	32,914,288	33,506,394
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment in loans and leases, individually evaluated for impairment	204,916	201,479
Recorded investment in loans and leases, collectively evaluated for impairment	19,638,576	21,871,726
Recorded investment in loans and leases, purchased impaired	421,670	517,707
Loans and leases, net of unearned discount	20,265,162	22,590,912
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment in loans and leases, individually evaluated for impairment	65,632	65,466
Recorded investment in loans and leases, collectively evaluated for impairment	12,936,801	12,080,597
Loans and leases, net of unearned discount	$ 13,002,433	$ 12,146,063

Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) Modification	Sep. 30, 2016 USD ($) Modification	Sep. 30, 2017 USD ($) Modification	Sep. 30, 2016 USD ($) Modification
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	147	134	506	569
Pre-modification recorded investment	$ 29,812	$ 93,640	$ 179,726	$ 235,214
Post- modification	$ 29,857	$ 83,898	$ 158,912	$ 224,499
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	17	18	67	55
Pre-modification recorded investment	$ 5,861	$ 14,925	$ 38,608	$ 36,984
Post- modification	5,738	14,258	38,393	35,924
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	11,516	57,474	49,250	150,790
Principal Deferral [Member] \| Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	1,420	11,644	16,193	17,802
Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	965		7,818	4,676
Other [Member] \| Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	868		868	4,576
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	17,376	26,424	101,844	69,033
Combination of Concession Types [Member] \| Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 3,450	$ 2,614	$ 21,332	$ 13,546
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	49	43	162	112
Pre-modification recorded investment	$ 15,812	$ 69,486	$ 93,346	$ 148,204
Post- modification	15,236	59,985	72,119	138,532
Commercial, Financial, Leasing, etc. [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	5,888	40,183	18,449	98,561
Commercial, Financial, Leasing, etc. [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	97		6,459
Commercial, Financial, Leasing, etc. [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 9,251	$ 19,802	$ 47,211	$ 39,971
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	34	30	105	73
Pre-modification recorded investment	$ 5,123	$ 5,638	$ 22,459	$ 11,946
Post- modification	5,749	5,928	24,165	12,650
Residential [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	3,033	4,714	11,608	7,945
Residential [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 2,716	$ 1,214	$ 12,557	$ 4,705
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	4	6	17	14
Pre-modification recorded investment	$ 515	$ 827	$ 3,724	$ 2,415
Post- modification	550	963	3,970	2,675
Residential Limited Documentation [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	383	470	618	803
Residential Limited Documentation [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 167	$ 493	$ 3,352	$ 1,872
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	25	26	85	84
Pre-modification recorded investment	$ 2,154	$ 2,552	$ 7,885	$ 9,189
Post- modification	2,237	2,552	7,973	9,189
Home Equity Lines and Loans [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	461	251	1,040	655
Home Equity Lines and Loans [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			491
Home Equity Lines and Loans [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 1,776	$ 2,301	$ 6,442	$ 8,534
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	17	10	59	148
Pre-modification recorded investment	$ 342	$ 186	$ 1,160	$ 1,005
Post- modification	342	186	1,160	1,005
Automobile [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	326	$ 186	1,089	865
Automobile [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				55
Automobile [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 16		$ 71	$ 85
Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification	1	1	6	78
Pre-modification recorded investment	$ 5	$ 26	$ 85	$ 1,192
Post- modification	5	26	85	1,192
Other [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 5	$ 26	$ 85	951
Other [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				45
Other [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				$ 196
Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification			3	3
Pre-modification recorded investment			$ 12,291	$ 23,905
Post- modification			10,879	22,958
Residential Builder and Developer [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				$ 22,958
Residential Builder and Developer [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			$ 10,879
Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications \| Modification			2	2
Pre-modification recorded investment			$ 168	$ 374
Post- modification			168	374
Other Commercial Construction [Member] \| Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			$ 168	250
Other Commercial Construction [Member] \| Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification				$ 124

Borrowings - Additional Information (Detail) - USD ($) $ in Millions			1 Months Ended	9 Months Ended
	Aug. 31, 2017	Jun. 30, 2017	May 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Junior subordinated debentures				$ 519
Debt Maturity, Start Year				Jan. 01, 2027
Debt Maturity, End Year				Dec. 31, 2033
Agreements to repurchase securities				$ 425	$ 1,100
Collateral posted				$ 445	$ 1,100
Bank Note Program [Member]
Debt Instrument [Line Items]
Senior notes			$ 900
Debt instrument maturity year			May 31, 2022
Bank Note Program Fixed Interest Rate [Member]
Debt Instrument [Line Items]
Senior notes			$ 650
Fixed interest rate			2.50%
Fixed Rate Senior Notes Due August 2020 [Member]
Debt Instrument [Line Items]
Senior notes	$ 750
Fixed interest rate	2.05%
Debt instrument maturity year	Aug. 31, 2020
Debt instrument maturity period	3 years
Fixed Rate Subordinated Notes Due August 2027 [Member]
Debt Instrument [Line Items]
Fixed interest rate	3.40%
Debt instrument maturity year	Aug. 31, 2027
Debt instrument maturity period	10 years
Subordinated notes	$ 500
London Interbank Offered Rate (LIBOR) [Member] \| Bank Note Program Variable Interest Rate [Member]
Debt Instrument [Line Items]
Senior notes			$ 250
Fixed Rate Senior Notes [Member]
Debt Instrument [Line Items]
Fixed interest rate		1.40%
Debt instrument maturity year		Jul. 25, 2017
Repayments of senior notes		$ 750
Debt instrument, redemption, description				The notes had a maturity date of July 25, 2017 and were redeemable on or after the 30th day prior to the maturity date.

Shareholders' Equity - Additional Information (Detail) - $ / shares	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, par value	$ 1.00	$ 1.00
Warrant [Member] \| Assumed In Acquisition [Member]
Class of Stock [Line Items]
Exercise price of each class of warrants or rights outstanding	$ 518.47
Warrant to purchase common stock	95,472
Warrants, year of expiration	2018

Shareholders' Equity - Issued and Outstanding Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Carrying Value	$ 1,231,500	$ 1,231,500
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, Shares Issued	230,000	230,000
Preferred stock, Shares Outstanding	230,000	230,000
Carrying Value	$ 230,000	$ 230,000
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, Shares Issued	151,500	151,500
Preferred stock, Shares Outstanding	151,500	151,500
Carrying Value	$ 151,500	$ 151,500
Series E Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, Shares Issued	350,000	350,000
Preferred stock, Shares Outstanding	350,000	350,000
Carrying Value	$ 350,000	$ 350,000
Series F Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, Shares Issued	50,000	50,000
Preferred stock, Shares Outstanding	50,000	50,000
Carrying Value	$ 500,000	$ 500,000

Shareholders' Equity - Issued and Outstanding Preferred Stock (Parenthetical) (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Preferred stock dividend rate	6.375%	6.375%
Exercise price of each class of warrants or rights outstanding	$ 73.79	$ 73.79
Warrants and rights outstanding	327,358
Warrants, year of expiration	2018	2018
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Preferred stock dividend rate	6.375%	6.375%
Series E Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Preferred stock dividend rate	6.45%	6.45%
Date of change in the dividend rate	Feb. 14, 2024	Feb. 14, 2024
London Interbank offered rate plus basis points	3.61%	3.61%
Preferred shares redemption date	Feb. 15, 2024	Feb. 15, 2024
Preferred Stock, Redemption Feature, Redemption Term	90 days	90 days
Series F Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 10,000	$ 10,000
Preferred stock dividend rate	5.125%	5.125%
Date of change in the dividend rate	Oct. 31, 2026	Oct. 31, 2026
London Interbank offered rate plus basis points	3.52%	3.52%
Preferred shares redemption date	Nov. 01, 2026	Nov. 01, 2026
Preferred Stock, Redemption Feature, Redemption Term	90 days	90 days

Pension Plans and Other Postretirement Benefits - Net Periodic Defined Benefit Cost for Defined Benefit Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,048	$ 6,259	$ 15,145	$ 18,778
Interest cost on projected benefit obligation	19,818	20,853	59,452	62,558
Expected return on plan assets	(27,131)	(27,118)	(81,393)	(81,355)
Amortization of prior service cost (credit)	139	(807)	418	(2,421)
Amortization of net actuarial loss (gain)	7,316	7,536	21,947	22,609
Net periodic benefit cost	5,190	6,723	15,569	20,169
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	293	399	878	1,197
Interest cost on projected benefit obligation	929	1,242	2,787	3,728
Amortization of prior service cost (credit)	(340)	(339)	(1,019)	(1,019)
Amortization of net actuarial loss (gain)	(247)	15	(741)	45
Net periodic benefit cost	$ 635	$ 1,317	$ 1,905	$ 3,951

Pension Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Compensation And Retirement Disclosure [Abstract]
Defined contribution pension and retirement savings plans total expense	$ 16,085,000	$ 14,783,000	$ 53,127,000	$ 47,747,000

Earnings Per Common Share - Computations of Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income available to common shareholders:
Net income	$ 355,923	$ 349,984	$ 1,085,903	$ 984,543
Less: Preferred stock dividends	(18,130)	(20,318)	(54,604)	(60,953)
Net income available to common equity	337,793	329,666	1,031,299	923,590
Less: Income attributable to unvested stock-based compensation awards	(1,992)	(2,674)	(6,288)	(7,920)
Net income available to common shareholders	$ 335,801	$ 326,992	$ 1,025,011	$ 915,670
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	152,245	156,767	153,814	158,710
Less: Unvested stock-based compensation awards	(898)	(1,274)	(948)	(1,374)
Weighted-average shares outstanding	151,347	155,493	152,866	157,336
Basic earnings per common share	$ 2.22	$ 2.10	$ 6.71	$ 5.82

Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income available to common equity	$ 337,793	$ 329,666	$ 1,031,299	$ 923,590
Less: Income attributable to unvested stock-based compensation awards	(1,989)	(2,668)	(6,276)	(7,904)
Net income available to common shareholders	$ 335,804	$ 326,998	$ 1,025,023	$ 915,686
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	152,245	156,767	153,814	158,710
Less: Unvested stock-based compensation awards	(898)	(1,274)	(948)	(1,374)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	344	533	427	507
Adjusted weighted-average shares outstanding	151,691	156,026	153,293	157,843
Diluted earnings per common share	$ 2.21	$ 2.10	$ 6.69	$ 5.80

Earnings Per Common Share - Additional Information (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	408,657	2,015,870	404,487	2,513,288

Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			$ (485,245)	$ (414,545)
Unrealized holding gains (losses), before tax			53,221	235,666
Foreign currency translation adjustment, before tax			3,829	(2,836)
Unrealized losses on cash flow hedges, before tax			(1,076)
Total other comprehensive income (loss) before reclassifications, before tax			55,974	232,830
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, before tax			2,535	2,998
(Gains) losses realized in net income, before tax			17	(28,748)
Accretion of net gain (losses) on terminated cash flow hedges, before tax			(109)	(116)
Net yield adjustment from cash flow hedges currently in effect, before tax			(2,275)
Amortization of prior service credit, before tax			(601)	(3,440)
Amortization of actuarial losses, before tax			21,206	22,654
Total reclassifications, before tax			20,773	(6,652)
Total gain (loss) during the period, before tax			76,747	226,178
Ending balance, before tax	$ (408,498)	$ (188,367)	(408,498)	(188,367)
Beginning balance, tax			190,609	162,918
Unrealized holding gains (losses), tax			(20,934)	(92,714)
Foreign currency translation adjustment, tax			(1,340)	989
Unrealized losses on cash flow hedges, tax			424
Total other comprehensive income (loss) before reclassifications, tax			(21,850)	(91,725)
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, tax			(998)	(1,180)
(Gains) losses realized in net income, before tax			(7)	11,309
Accretion of net gain (losses) on terminated cash flow hedges, tax			43	46
Net yield adjustment from cash flow hedges currently in effect, tax			895
Amortization of prior service credit, tax			236	1,354
Amortization of actuarial losses, tax			(8,345)	(8,914)
Total reclassifications, tax			(8,176)	2,615
Total gain (loss) during the period, tax			(30,026)	(89,110)
Ending balance, tax	160,583	73,808	160,583	73,808
Total other comprehensive income (loss) before reclassifications, tax			(21,850)	(91,725)
Beginning balance, net of tax			(294,636)	(251,627)
Unrealized holding gains (losses), net			32,287	142,952
Foreign currency translation adjustment, net of tax	863	(229)	2,489	(1,847)
Unrealized losses on cash flow hedges, net of tax			(652)
Total other comprehensive income (loss) before reclassifications, net of tax			34,124	141,105
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, net of tax			1,537	1,818
(Gains) losses realized in net income, before tax			10	(17,439)
Accretion of net gain on terminated cash flow hedges, net of tax			(66)	(70)
Net yield adjustment from cash flow hedges currently in effect, net of tax			(1,380)
Amortization of prior service credit, net of tax			(365)	(2,086)
Amortization of actuarial losses, net of tax			12,861	13,740
Total reclassifications, net of tax			12,597	(4,037)
Total other comprehensive income (loss)	22,166	(13,538)	46,721	137,068
Ending balance, net of tax	(247,915)	(114,559)	(247,915)	(114,559)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			46,725	16,359
Unrealized holding gains (losses), before tax			(7,365)	1,228
Total other comprehensive income (loss) before reclassifications, before tax			(7,365)	1,228
(Gains) losses realized in net income, before tax			(50)
Total reclassifications, before tax			(50)
Total gain (loss) during the period, before tax			(7,415)	1,228
Ending balance, before tax	39,310	17,587	39,310	17,587
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(73,785)	62,849
Unrealized holding gains (losses), before tax			60,586	234,438
Total other comprehensive income (loss) before reclassifications, before tax			60,586	234,438
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, before tax			2,535	2,998
(Gains) losses realized in net income, before tax			67	(28,748)
Total reclassifications, before tax			2,602	(25,750)
Total gain (loss) during the period, before tax			63,188	208,688
Ending balance, before tax	(10,597)	271,537	(10,597)	271,537
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(449,917)	(489,660)
Amortization of prior service credit, before tax			(601)	(3,440)
Amortization of actuarial losses, before tax			21,206	22,654
Total reclassifications, before tax			20,605	19,214
Total gain (loss) during the period, before tax			20,605	19,214
Ending balance, before tax	(429,312)	(470,446)	(429,312)	(470,446)
Total other comprehensive income (loss)			12,496
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(8,268)	(4,093)
Foreign currency translation adjustment, before tax			3,829	(2,836)
Unrealized losses on cash flow hedges, before tax			(1,076)
Total other comprehensive income (loss) before reclassifications, before tax			2,753	(2,836)
Accretion of net gain (losses) on terminated cash flow hedges, before tax			(109)	(116)
Net yield adjustment from cash flow hedges currently in effect, before tax			(2,275)
Total reclassifications, before tax			(2,384)	(116)
Total gain (loss) during the period, before tax			369	(2,952)
Ending balance, before tax	$ (7,899)	$ (7,045)	$ (7,899)	$ (7,045)

Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 16,486,622	$ 16,173,289
Net gain (loss) during period	$ 22,166	$ (13,538)	46,721	137,068
Ending balance	16,318,052	16,340,976	16,318,052	16,340,976
Investment Securities With OTTI [Member] \| Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			28,338
Net gain (loss) during period			(4,496)
Ending balance	23,842		23,842
Investment Securities All Other [Member] \| Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(44,657)
Net gain (loss) during period			38,330
Ending balance	(6,327)		(6,327)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(272,874)
Net gain (loss) during period			12,496
Ending balance	(260,378)		(260,378)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(5,443)
Net gain (loss) during period			391
Ending balance	(5,052)		(5,052)
Accumulated Other Comprehensive Income (Loss), Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(294,636)	(251,627)
Net gain (loss) during period			46,721
Ending balance	$ (247,915)	$ (114,559)	$ (247,915)	$ (114,559)

Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 6,950,000,000		$ 6,950,000,000
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans	27,000,000		27,000,000		$ 28,000,000
Aggregate fair value of derivative financial instruments in a liability position	17,000,000		17,000,000		34,000,000
Net liability positions with counterparties	17,000,000		17,000,000		30,000,000
Aggregate fair value of derivative financial instruments in asset position	7,000,000		7,000,000		15,000,000
Net fair value of derivative financial instruments in a net asset position	7,000,000		7,000,000		11,000,000
Collateral relating to net asset positions	5,000,000		5,000,000		9,000,000
Counterparties [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	18,000,000		18,000,000		27,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Amount of initial margin posted	49,000,000		49,000,000		111,000,000
Net fair value of derivative financial instruments in a net asset position	1,000,000		1,000,000		63,000,000
Collateral relating to net asset positions	1,000,000		1,000,000		81,000,000
Reduction in the fair value of derivative asset due to contractual settlements			(89,000,000)
Reduction in the fair value of derivative liability due to contractual settlements			(45,000,000)
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	7,000,000	$ 9,000,000	18,000,000	$ 30,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	15,500,000,000		15,500,000,000		21,600,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	545,000,000		545,000,000		$ 471,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Amount of initial margin posted	0		0
Fair value of additional collateral to be posted for derivative financial instruments	0		0
Credit Risk Derivative [Member] \| Maximum [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	$ 1,000,000		$ 1,000,000

Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional Amount	$ 6,950,000,000
Average Maturity (in years)	2 years 6 months
Estimated Fair Value Gain (Loss)	$ 697,000
Variable Rate Commercial Real Estate Loans [Member] \| Cash Flow Hedges [Member]
Derivative [Line Items]
Notional Amount	$ 2,000,000,000
Average Maturity (in years)	1 year 7 months 6 days
Weighted-Average Rate, Fixed	1.46%
Weighted-Average Rate, Variable	1.24%
Fixed Rate Long-Term Borrowings [Member] \| Fair Value Hedges [Member]
Derivative [Line Items]
Notional Amount	$ 4,950,000,000	$ 900,000,000
Average Maturity (in years)	2 years 10 months 25 days	1 year 1 month 6 days
Weighted-Average Rate, Fixed	2.63%	3.75%
Weighted-Average Rate, Variable	2.04%	2.08%
Estimated Fair Value Gain (Loss)	$ 697,000	$ 11,892,000

Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Parenthetical) (Detail) $ in Millions	Sep. 30, 2017 USD ($)
Fair Value Hedges [Member]
Derivative [Line Items]
Reduction of estimated fair value losses on hedging instruments	$ 12.2
Cash Flow Hedges [Member]
Derivative [Line Items]
Reduction of estimated fair value losses on hedging instruments	$ 3.4

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 131,831	$ 295,069
Liability Derivatives, Fair Value	113,808	176,857
Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	3,715	45,081
Liability Derivatives, Fair Value	2,902	1,347
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	128,116	249,988
Liability Derivatives, Fair Value	110,906	175,510
Interest Rate Swap Agreements [Member] \| Fair Value Hedges [Member] \| Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	2,048	11,892
Liability Derivatives, Fair Value	1,351
Commitments to Sell Real Estate Loans [Member] \| Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	3,153	5,210
Liability Derivatives, Fair Value	936	399
Commitments to Sell Real Estate Loans [Member] \| Fair Value Hedges [Member] \| Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	1,667	33,189
Liability Derivatives, Fair Value	1,551	1,347
Mortgage-Related Commitments to Originate Real Estate Loans for Sale [Member] \| Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	13,962	8,060
Liability Derivatives, Fair Value	240	735
Interest Rate Contracts [Member] \| Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	104,178	228,810
Liability Derivatives, Fair Value	103,825	167,737
Foreign Exchange and Other Option and Futures Contracts [Member] \| Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	6,823	7,908
Liability Derivatives, Fair Value	$ 5,905	$ 6,639

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Parenthetical) (Detail) $ in Millions	Sep. 30, 2017 USD ($)
Offsetting [Abstract]
Reduction in estimated fair value of interest rate swaps in asset position	$ 89.3
Reduction in estimated fair value of interest rate swaps in liability position	$ 29.2

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Statement of Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 944	$ 6,568	$ 7,129	$ 16,993
Interest Rate Swap Agreements [Member] \| Fixed Rate Long-Term Borrowings [Member] \| Derivatives Designated and Qualifying as Hedging Instruments [Member] \| Fair Value Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives in fair value hedging relationships, Derivatives	(13,509)	(12,588)	(23,423)	(22,832)
Derivatives in fair value hedging relationships, Hedged item	14,026	12,587	23,049	21,603
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	(418)	4,822	2,363	11,578
Foreign Exchange and Other Option and Futures Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 1,362	$ 1,746	$ 4,766	$ 5,415

Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Variable Interest Entity Disclosure [Abstract]
Other assets for its "investment" in the common securities recognized by the company of various trusts	$ 24,000,000		$ 24,000,000		$ 24,000,000
Total assets of partnerships in which the company invested	1,000,000,000		1,000,000,000		1,000,000,000
Maximum exposure to loss of investments in real estate partnerships	329,000,000		329,000,000		294,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	118,000,000		118,000,000		$ 102,000,000
Investments amortized to income tax expense	11,000,000	$ 13,000,000	35,000,000	$ 34,000,000
Federal tax credits and other federal tax benefits recognized	$ 16,000,000	$ 18,000,000	$ 47,000,000	$ 46,000,000

Fair Value Measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets	$ 170,516	$ 323,867
Investment securities	11,416,824	13,332,072
U.S. Treasury and Federal Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	2,007,117	1,902,544
Obligations of States and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	2,678	3,641
Government Issued or Guaranteed [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	9,184,483	10,954,861
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	128,530	118,516
Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	93,986	352,466
Fair Value Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets	170,516	323,867
Investment securities	11,416,824	13,332,072
Real estate loans held for sale	571,199	1,056,180
Other assets	20,830	58,351
Total assets	12,179,369	14,770,470
Trading account liabilities	109,730	174,376
Other liabilities	4,078	2,481
Total liabilities	113,808	176,857
Fair Value Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets	47,927	46,135
Investment securities	50,917	301,711
Total assets	98,844	347,846
Fair Value Measurements, Recurring [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets	122,589	277,732
Investment securities	11,365,877	13,030,317
Real estate loans held for sale	571,199	1,056,180
Other assets	6,868	50,291
Total assets	12,066,533	14,414,520
Trading account liabilities	109,730	174,376
Other liabilities	3,838	1,746
Total liabilities	113,568	176,122
Fair Value Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	30	44
Other assets	13,962	8,060
Total assets	13,992	8,104
Other liabilities	240	735
Total liabilities	240	735
Fair Value Measurements, Recurring [Member] \| U.S. Treasury and Federal Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	2,007,117	1,902,544
Fair Value Measurements, Recurring [Member] \| U.S. Treasury and Federal Agencies [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	2,007,117	1,902,544
Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	2,678	3,641
Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	2,678	3,641
Fair Value Measurements, Recurring [Member] \| Government Issued or Guaranteed [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	9,184,483	10,954,861
Fair Value Measurements, Recurring [Member] \| Government Issued or Guaranteed [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	9,184,483	10,954,861
Fair Value Measurements, Recurring [Member] \| Privately Issued Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	30	44
Fair Value Measurements, Recurring [Member] \| Privately Issued Mortgage-Backed Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	30	44
Fair Value Measurements, Recurring [Member] \| Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	128,530	118,516
Fair Value Measurements, Recurring [Member] \| Other Debt Securities [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	128,530	118,516
Fair Value Measurements, Recurring [Member] \| Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	93,986	352,466
Fair Value Measurements, Recurring [Member] \| Equity Securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	50,917	301,711
Fair Value Measurements, Recurring [Member] \| Equity Securities [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	$ 43,069	$ 50,755

Fair Value Measurements - Changes in Level 3 Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - Fair Value Measurements, Recurring [Member] - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Privately Issued [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 35	$ 57	$ 44	$ 74
Total gains (losses) realized/unrealized:
Settlements	(5)	(6)	(14)	(23)
Ending Balance	30	51	30	51
Other Assets and Other Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	12,425	21,383	7,325	9,879
Total gains (losses) realized/unrealized:
Included in earnings	22,313	45,534	65,824	104,862
Transfers in and/or out of Level 3 (a)	(21,016)	(37,117)	(59,427)	(84,941)
Ending Balance	13,722	29,800	13,722	29,800
Changes in unrealized gains included in earnings related to assets still held at end of period	$ 12,659	27,663	$ 13,684	29,288
Collateralized Debt Obligations [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		43,305		47,393
Total gains (losses) realized/unrealized:
Included in earnings		28,475		28,475
Included in other comprehensive income		(15,050)		(18,268)
Sales		$ (56,730)		(56,730)
Settlements				$ (870)

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rates for fair value estimations			15.00%
Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rates for fair value estimations			90.00%
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves	$ 16	$ 20	$ 55	$ 42
Fair Value, Measurements, Nonrecurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	184	249	184	249	$ 293
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	36	53	36	53
Fair Value, Measurements, Nonrecurring [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	105	144	105	144	153
Fair Value, Measurements, Nonrecurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	$ 79	$ 105	$ 79	$ 105	$ 140

Fair Value Measurements - Quantitative Information Related to Significant Unobservable Inputs (Detail) - Fair Value Measurements, Recurring [Member] - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Privately Issued [Member] \| Two Independent Pricing Quotes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Recurring fair value measurements for certain Level 3 Assets and Liabilities	$ 30	$ 44
Other Assets and Other Liabilities [Member] \| Discounted Cash Flows [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Recurring fair value measurements for certain Level 3 Assets and Liabilities	$ 13,722	$ 7,325
Other Assets and Other Liabilities [Member] \| Discounted Cash Flows [Member] \| Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Commitment expirations	0.00%	0.00%
Other Assets and Other Liabilities [Member] \| Discounted Cash Flows [Member] \| Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Commitment expirations	80.00%	77.00%
Other Assets and Other Liabilities [Member] \| Discounted Cash Flows [Member] \| Weighted Average [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Commitment expirations	28.00%	30.00%

Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Financial assets:
Cash and cash equivalents	$ 1,368,252		$ 1,320,549	$ 1,332,202		$ 1,368,040
Interest-bearing deposits at banks	6,306,484		5,000,638
Trading account assets	170,516		323,867
Investment securities	15,073,926		16,250,468
Loans and leases:
Allowance for credit losses	(1,013,326)	$ (1,008,225)	(988,997)	$ (976,121)	$ (970,496)	$ (955,992)
Loans and leases, net	86,911,808		89,864,419
Financial liabilities:
Noninterest-bearing deposits	(33,111,246)		(32,813,896)
Savings and interest-checking deposits	(52,936,615)		(52,346,207)
Time deposits	(7,233,518)		(10,131,846)
Deposits at Cayman Islands office	(232,014)		(201,927)
Short-term borrowings	(200,768)		(163,442)
Long-term borrowings	(8,577,645)		(9,493,835)
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,368,252		1,320,549
Interest-bearing deposits at banks	6,306,484		5,000,638
Trading account assets	170,516		323,867
Investment securities	15,073,926		16,250,468
Loans and leases:
Commercial loans and leases	21,743,251		22,610,047
Commercial real estate loans	32,914,288		33,506,394
Residential real estate loans	20,265,162		22,590,912
Consumer loans	13,002,433		12,146,063
Allowance for credit losses	(1,013,326)		(988,997)
Loans and leases, net	86,911,808		89,864,419
Accrued interest receivable	325,982		308,805
Financial liabilities:
Noninterest-bearing deposits	(33,111,246)		(32,813,896)
Savings and interest-checking deposits	(52,936,615)		(52,346,207)
Time deposits	(7,233,518)		(10,131,846)
Deposits at Cayman Islands office	(232,014)		(201,927)
Short-term borrowings	(200,768)		(163,442)
Long-term borrowings	(8,577,645)		(9,493,835)
Accrued interest payable	(69,290)		(75,172)
Trading account liabilities	(109,730)		(174,376)
Other financial instruments:
Commitments to originate real estate loans for sale	13,722		7,325
Commitments to sell real estate loans	2,333		36,653
Other credit-related commitments	(119,938)		(136,295)
Interest rate swap agreements used for interest rate risk management	697		11,892
Estimate Fair Value [Member]
Financial assets:
Cash and cash equivalents	1,368,252		1,320,549
Interest-bearing deposits at banks	6,306,484		5,000,638
Trading account assets	170,516		323,867
Investment securities	15,079,756		16,244,412
Loans and leases:
Commercial loans and leases	21,409,984		22,239,428
Commercial real estate loans	32,507,319		33,129,428
Residential real estate loans	20,369,392		22,638,167
Consumer loans	12,935,924		12,061,590
Loans and leases, net	87,222,619		90,068,613
Accrued interest receivable	325,982		308,805
Financial liabilities:
Noninterest-bearing deposits	(33,111,246)		(32,813,896)
Savings and interest-checking deposits	(52,936,615)		(52,346,207)
Time deposits	(7,294,182)		(10,222,585)
Deposits at Cayman Islands office	(232,014)		(201,927)
Short-term borrowings	(200,768)		(163,442)
Long-term borrowings	(8,630,195)		(9,473,844)
Accrued interest payable	(69,290)		(75,172)
Trading account liabilities	(109,730)		(174,376)
Other financial instruments:
Commitments to originate real estate loans for sale	13,722		7,325
Commitments to sell real estate loans	2,333		36,653
Other credit-related commitments	(119,938)		(136,295)
Interest rate swap agreements used for interest rate risk management	697		11,892
Estimate Fair Value [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,290,532		1,249,654
Trading account assets	47,927		46,135
Investment securities	50,917		301,711
Estimate Fair Value [Member] \| Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	77,720		70,895
Interest-bearing deposits at banks	6,306,484		5,000,638
Trading account assets	122,589		277,732
Investment securities	14,916,360		15,821,176
Loans and leases:
Commercial real estate loans	223,659		642,590
Residential real estate loans	4,557,929		4,912,488
Loans and leases, net	4,781,588		5,555,078
Accrued interest receivable	325,982		308,805
Financial liabilities:
Noninterest-bearing deposits	(33,111,246)		(32,813,896)
Savings and interest-checking deposits	(52,936,615)		(52,346,207)
Time deposits	(7,294,182)		(10,222,585)
Deposits at Cayman Islands office	(232,014)		(201,927)
Short-term borrowings	(200,768)		(163,442)
Long-term borrowings	(8,630,195)		(9,473,844)
Accrued interest payable	(69,290)		(75,172)
Trading account liabilities	(109,730)		(174,376)
Other financial instruments:
Commitments to sell real estate loans	2,333		36,653
Interest rate swap agreements used for interest rate risk management	697		11,892
Estimate Fair Value [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Investment securities	112,479		121,525
Loans and leases:
Commercial loans and leases	21,409,984		22,239,428
Commercial real estate loans	32,283,660		32,486,838
Residential real estate loans	15,811,463		17,725,679
Consumer loans	12,935,924		12,061,590
Loans and leases, net	82,441,031		84,513,535
Other financial instruments:
Commitments to originate real estate loans for sale	13,722		7,325
Other credit-related commitments	$ (119,938)		$ (136,295)

Commitments and Contingencies - Company's Significant Commitments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Commitments to extend credit
Home equity lines of credit	$ 5,492,892	$ 5,499,609
Commercial real estate loans to be sold	170,786	70,100
Other commercial real estate	5,749,428	6,451,709
Residential real estate loans to be sold	482,650	478,950
Other residential real estate	202,702	232,721
Commercial and other	12,677,838	12,298,473
Standby letters of credit	2,657,352	2,987,091
Commercial letters of credit	42,684	44,723
Financial guarantees and indemnification contracts	3,385,498	3,043,580
Commitments to sell real estate loans	$ 1,052,472	$ 1,489,237

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	$ 3,200,000,000	$ 2,800,000,000
Minimum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses	0
Maximum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses	$ 50,000,000

Segment Information - Summary of Reclassified Segment Information on Comparable Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Net income	$ 355,923	$ 349,984	$ 1,085,903	$ 984,543
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,416,563	1,349,690	4,176,684	3,954,660
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income	31,408	24,024	85,146	77,340
Business Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	130,501	120,901	375,816	357,584
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income	109,797	102,704	328,211	309,264
Commercial Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	267,822	268,528	818,846	787,358
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income	97,295	90,065	269,113	254,682
Commercial Real Estate [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	212,014	205,562	604,437	575,117
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income	31,515	45,551	95,200	134,575
Discretionary Portfolio [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	65,808	105,585	216,798	295,620
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income	13,546	15,865	37,206	43,055
Residential Mortgage Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	90,018	96,675	264,120	280,854
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income	96,329	74,753	282,614	219,234
Retail Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	392,542	361,864	1,144,964	1,062,923
All Other [Member]
Segment Reporting Information [Line Items]
Net income	(23,967)	(2,978)	(11,587)	(53,607)
All Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ 257,858	190,575	$ 751,703	595,204
As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		349,984		984,543
As Previously Reported [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		1,349,690		3,954,660
As Previously Reported [Member] \| Business Banking [Member]
Segment Reporting Information [Line Items]
Net income		21,422		69,617
As Previously Reported [Member] \| Business Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		116,513		344,562
As Previously Reported [Member] \| Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income		102,796		309,515
As Previously Reported [Member] \| Commercial Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		268,683		787,781
As Previously Reported [Member] \| Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income		90,065		254,682
As Previously Reported [Member] \| Commercial Real Estate [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		205,562		575,117
As Previously Reported [Member] \| Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income		50,773		151,522
As Previously Reported [Member] \| Discretionary Portfolio [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		114,391		324,195
As Previously Reported [Member] \| Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income		22,924		59,981
As Previously Reported [Member] \| Residential Mortgage Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		108,576		309,393
As Previously Reported [Member] \| Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income		69,506		204,291
As Previously Reported [Member] \| Retail Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		353,016		1,037,727
As Previously Reported [Member] \| All Other [Member]
Segment Reporting Information [Line Items]
Net income		(7,502)		(65,065)
As Previously Reported [Member] \| All Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		182,949		575,885
Impact of Changes [Member] \| Business Banking [Member]
Segment Reporting Information [Line Items]
Net income		2,602		7,723
Impact of Changes [Member] \| Business Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		4,388		13,022
Impact of Changes [Member] \| Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income		(92)		(251)
Impact of Changes [Member] \| Commercial Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		(155)		(423)
Impact of Changes [Member] \| Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income		(5,222)		(16,947)
Impact of Changes [Member] \| Discretionary Portfolio [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		(8,806)		(28,575)
Impact of Changes [Member] \| Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income		(7,059)		(16,926)
Impact of Changes [Member] \| Residential Mortgage Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		(11,901)		(28,539)
Impact of Changes [Member] \| Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income		5,247		14,943
Impact of Changes [Member] \| Retail Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		8,848		25,196
Impact of Changes [Member] \| All Other [Member]
Segment Reporting Information [Line Items]
Net income		4,524		11,458
Impact of Changes [Member] \| All Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		$ 7,626		$ 19,319

Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 355,923	$ 349,984	$ 1,085,903	$ 984,543
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,416,563	1,349,690	4,176,684	3,954,660
Business Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	31,408	24,024	85,146	77,340
Business Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	130,501	120,901	375,816	357,584
Business Banking [Member] \| Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	919	1,086	2,836	3,274
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	109,797	102,704	328,211	309,264
Commercial Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	267,822	268,528	818,846	787,358
Commercial Banking [Member] \| Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	840	950	2,603	2,917
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	97,295	90,065	269,113	254,682
Commercial Real Estate [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	212,014	205,562	604,437	575,117
Commercial Real Estate [Member] \| Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	401	463	1,165	1,299
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	31,515	45,551	95,200	134,575
Discretionary Portfolio [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	65,808	105,585	216,798	295,620
Discretionary Portfolio [Member] \| Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(12,346)	(14,795)	(37,670)	(43,726)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	13,546	15,865	37,206	43,055
Residential Mortgage Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	90,018	96,675	264,120	280,854
Residential Mortgage Banking [Member] \| Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	18,866	22,051	55,221	62,955
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	96,329	74,753	282,614	219,234
Retail Banking [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	392,542	361,864	1,144,964	1,062,923
Retail Banking [Member] \| Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	2,668	3,052	8,760	9,198
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	(23,967)	(2,978)	(11,587)	(53,607)
All Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	257,858	190,575	751,703	595,204
All Other [Member] \| Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (11,348)	$ (12,807)	$ (32,915)	$ (35,917)

Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Segment Reporting Information [Line Items]
Average Assets	$ 121,073	$ 124,340	$ 123,897
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	5,596	5,456	5,442
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	26,699	25,592	25,363
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Assets	22,800	21,131	20,571
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Assets	37,807	40,867	41,253
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	2,335	2,569	2,578
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	12,519	11,840	11,739
All Other [Member]
Segment Reporting Information [Line Items]
Average Assets	$ 13,317	$ 16,885	$ 16,951

Segment Information - Summary of Segment Information (Parenthetical) (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting [Abstract]
Taxable-equivalent adjustment	$ 8,828,000	$ 6,725,000	$ 25,563,000	$ 19,579,000

Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Apr. 28, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 8,577,645		$ 8,577,645				$ 9,493,835
Bayview Lending Group [Member]
Schedule of Equity Method Investments [Line Items]
Minority interest in Bayview Lending Group LLC	20.00%		20.00%
Carrying value of minority interest investment in Bayview Lending Group LLC	$ 0		$ 0
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	3,200,000		3,200,000				3,500,000
Revenues from servicing	4,000	$ 5,000	13,000	$ 15,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	59,300,000		59,300,000				30,400,000
Revenues from sub-servicing	26,000	$ 25,000	74,000	$ 73,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	141,000		141,000				$ 158,000
Loan to Bayview Financial						$ 100,000
Bayview Financial [Member] \| Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount					$ 750,000
Bayview Financial [Member] \| Syndicated Loan Facility [Member] \| M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 88,000		$ 88,000

Recent Accounting Developments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Minimum lease payments under non cancelable operating lease		$ 467
Adoption of New Accounting Guidance [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reduction of Income tax expense	$ (18)