M&T Bank (MTB) 10-Q 5 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	MTB
Entity Registrant Name	M&T BANK CORP
Entity Central Index Key	36,270
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		140,357,696

Consolidated Balance Sheet (Una

Consolidated Balance Sheet (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 1,311,611	$ 1,420,888
Interest-bearing deposits at banks	6,523,746	5,078,903
Trading account	125,038	132,909
Investment securities (includes pledged securities that can be sold or repledged of $477,609 at September 30, 2018; $487,151 at December 31, 2017)
Available for sale (cost: $9,449,975 at September 30, 2018; $10,938,796 at December 31, 2017)	9,154,515	10,896,284
Held to maturity (fair value: $3,313,270 at September 30, 2018; $3,341,762 at December 31, 2017)	3,418,719	3,353,213
Equity and other securities (cost: $488,389 at September 30, 2018; $415,028 at December 31, 2017)	500,647	415,028
Total investment securities	13,073,881	14,664,525
Loans and leases	86,942,468	88,242,886
Unearned discount	(261,983)	(253,903)
Loans and leases, net of unearned discount	86,680,485	87,988,983
Allowance for credit losses	(1,019,488)	(1,017,198)
Loans and leases, net	85,660,997	86,971,785
Premises and equipment	634,424	646,451
Goodwill	4,593,112	4,593,112
Core deposit and other intangible assets	52,426	71,589
Accrued interest and other assets	4,852,402	5,013,325
Total assets	116,827,637	118,593,487
Liabilities
Noninterest-bearing deposits	31,773,560	33,975,180
Savings and interest-checking deposits	51,108,962	51,698,008
Time deposits	5,810,587	6,580,962
Deposits at Cayman Islands office	447,287	177,996
Total deposits	89,140,396	92,432,146
Short-term borrowings	1,310,110	175,099
Accrued interest and other liabilities	1,800,778	1,593,993
Long-term borrowings	9,140,268	8,141,430
Total liabilities	101,391,552	102,342,668
Shareholders' equity
Preferred stock, $1.00 par, 1,000,000 shares authorized; Issued and outstanding: Liquidation preference of $1,000 per share: 731,500 shares at September 30, 2018 and December 31, 2017; Liquidation preference of $10,000 per share: 50,000 shares at September 30, 2018 and December 31, 2017	1,231,500	1,231,500
Common stock, $.50 par, 250,000,000 shares authorized, 159,765,948 shares issued at September 30, 2018; 159,817,518 shares issued at December 31, 2017	79,883	79,909
Common stock issuable, 24,595 shares at September 30, 2018; 27,138 shares at December 31, 2017	1,716	1,847
Additional paid-in capital	6,585,447	6,590,855
Retained earnings	11,128,343	10,164,804
Accumulated other comprehensive income (loss), net	(542,399)	(363,814)
Treasury stock — common, at cost — 18,312,024 shares at September 30, 2018; 9,733,115 shares at December 31, 2017	(3,048,405)	(1,454,282)
Total shareholders’ equity	15,436,085	16,250,819
Total liabilities and shareholders’ equity	$ 116,827,637	$ 118,593,487

Consolidated Balance Sheet (U_2

Consolidated Balance Sheet (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Pledged securities that can be sold or repledged	$ 477,609	$ 487,151
Investment securities, available for sale, amortized cost	9,449,975	10,938,796
Investment securities, held to maturity, fair value	3,313,270	3,341,762
Equity and other securities, cost	$ 488,389	$ 415,028
Preferred stock, par value	$ 1	$ 1
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	159,765,948	159,817,518
Common stock issuable, shares	24,595	27,138
Treasury stock, common shares	18,312,024	9,733,115
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	50,000
Preferred stock, shares outstanding	50,000	50,000
Preferred stock, liquidation preference per share	$ 10,000	$ 10,000

Consolidated Statement of Incom

Consolidated Statement of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest income
Loans and leases, including fees	$ 1,060,832	$ 953,662	$ 3,065,272	$ 2,776,340
Investment securities
Fully taxable	80,118	87,937	244,989	276,057
Exempt from federal taxes	153	345	573	1,154
Deposits at banks	26,000	14,970	66,546	39,345
Other	272	296	1,050	760
Total interest income	1,167,375	1,057,210	3,378,430	3,093,656
Interest expense
Savings and interest-checking deposits	56,156	37,714	145,421	93,891
Time deposits	12,976	13,992	35,274	49,293
Deposits at Cayman Islands office	1,556	310	2,479	856
Short-term borrowings	1,600	554	3,866	1,148
Long-term borrowings	66,049	47,506	178,048	138,874
Total interest expense	138,337	100,076	365,088	284,062
Net interest income	1,029,038	957,134	3,013,342	2,809,594
Provision for credit losses	16,000	30,000	94,000	137,000
Net interest income after provision for credit losses	1,013,038	927,134	2,919,342	2,672,594
Other income
Brokerage services income	12,267	14,676	38,288	48,677
Trading account and foreign exchange gains	6,073	7,058	15,965	24,833
Loss on bank investment securities	(3,415)		(10,520)	(17)
Other revenues from operations	113,769	106,702	340,351	334,704
Total other income	459,294	459,429	1,375,404	1,367,090
Other expense
Salaries and employee benefits	431,371	398,605	1,313,336	1,246,400
Equipment and net occupancy	77,481	75,558	225,309	223,721
Outside data processing and software	50,678	45,761	148,819	134,637
FDIC assessments	18,849	23,969	58,689	78,149
Advertising and marketing	21,784	17,403	59,800	49,837
Printing, postage and supplies	8,843	8,732	26,881	27,397
Amortization of core deposit and other intangible assets	6,143	7,808	19,163	24,341
Other costs of operations	160,830	228,189	633,903	560,030
Total other expense	775,979	806,025	2,485,900	2,344,512
Income before taxes	696,353	580,538	1,808,846	1,695,172
Income taxes	170,262	224,615	436,985	609,269
Net income	526,091	355,923	1,371,861	1,085,903
Net income available to common shareholders
Basic	505,363	335,801	1,310,697	1,025,011
Diluted	$ 505,365	$ 335,804	$ 1,310,703	$ 1,025,023
Net income per common share
Basic	$ 3.54	$ 2.22	$ 9.01	$ 6.71
Diluted	3.53	2.21	9	6.69
Cash dividends per common share	$ 1	$ 0.75	$ 2.55	$ 2.25
Average common shares outstanding
Basic	142,822	151,347	145,424	152,866
Diluted	142,976	151,691	145,605	153,293
Mortgage Banking Revenues [Member]
Other income
Revenue from contract with customer	$ 88,408	$ 96,737	$ 268,213	$ 267,592
Service Charges on Deposit Accounts [Member]
Other income
Revenue from contract with customer	108,647	109,356	320,546	319,589
Trust Income [Member]
Other income
Revenue from contract with customer	$ 133,545	$ 124,900	$ 402,561	$ 371,712

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Partners Capital [Abstract]
Net income	$ 526,091	$ 355,923	$ 1,371,861	$ 1,085,903
Other comprehensive income, net of tax and reclassification adjustments:
Net unrealized gains (losses) on investment securities	(30,381)	18,258	(167,798)	33,834
Cash flow hedges adjustments	(961)	(1,120)	(13,972)	(2,098)
Foreign currency translation adjustment	(265)	863	(1,409)	2,489
Defined benefit plans liability adjustments	7,149	4,165	21,447	12,496
Total other comprehensive income (loss)	(24,458)	22,166	(161,732)	46,721
Total comprehensive income	$ 501,633	$ 378,089	$ 1,210,129	$ 1,132,624

Consolidated Statement of Cash

Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net income	$ 1,371,861	$ 1,085,903
Adjustments to reconcile net income to net cash provided by operating activities
Provision for credit losses	94,000	137,000
Depreciation and amortization of premises and equipment	80,186	84,631
Amortization of capitalized servicing rights	36,567	41,475
Amortization of core deposit and other intangible assets	19,163	24,341
Provision for deferred income taxes	(73,410)	9,926
Asset write-downs	7,398	10,878
Net gain on sales of assets	(17,681)	(27,967)
Net change in accrued interest receivable, payable	(30,178)	(23,059)
Net change in other accrued income and expense	125,478	110,138
Net change in loans originated for sale	(252,981)	523,895
Net change in trading account assets and liabilities	179,214	88,705
Net cash provided by operating activities	1,539,617	2,065,866
Cash flows from investing activities
Proceeds from sales of investment securities Available for sale	418	512,143
Proceeds from sales of investment securities equity and other	649,204	178,244
Proceeds from maturities of investment securities Available for sale	1,415,214	1,650,258
Proceeds from maturities of investment securities Held to maturity	374,718	390,278
Purchases of investment securities Available for sale	(9,197)	(248,705)
Purchases of investment securities Held to maturity	(444,703)	(1,175,608)
Purchases of investment securities equity and other	(644,404)	(132,104)
Net decrease (increase) in loans and leases	1,443,623	2,259,049
Net increase in interest-bearing deposits at banks	(1,444,843)	(1,305,846)
Capital expenditures, net	(59,302)	(62,515)
Net decrease in loan servicing advances	267,074	47,786
Other, net	(11,072)	66,357
Net cash provided by investing activities	1,536,730	2,179,337
Net decrease in deposits	(3,289,371)	(1,976,237)
Net increase in short-term borrowings	1,135,011	37,326
Proceeds from long-term borrowings	1,773,189	2,145,950
Payments on long-term borrowings	(707,594)	(3,029,320)
Purchases of treasury stock	(1,694,562)	(981,691)
Dividends paid - common	(371,380)	(345,166)
Dividends paid - preferred	(53,628)	(53,842)
Other, net	22,711	5,480
Net cash used by financing activities	(3,185,624)	(4,197,500)
Net increase (decrease) in cash, cash equivalents and restricted cash	(109,277)	47,703
Cash, cash equivalents and restricted cash at beginning of period	1,420,888	1,320,549
Cash, cash equivalents and restricted cash at end of period	1,311,611	1,368,252
Supplemental disclosure of cash flow information
Interest received during the period	3,360,710	3,088,042
Interest paid during the period	381,137	310,640
Income taxes paid during the period	197,247	462,163
Supplemental schedule of noncash investing and financing activities
Real estate acquired in settlement of loans	50,849	88,551
Securitization of residential mortgage loans allocated to Available-for-sale investment securities	17,606	22,527
Securitization of residential mortgage loans allocated to capitalized servicing rights	$ 275	$ 262

Consolidated Statement of Chang

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]	Additional Paid-in Capital [Member]Series A Warrants [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [Member]	Treasury Stock [Member]Series A Warrants [Member]
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)
Beginning balance at Dec. 31, 2017	16,250,819	1,231,500	79,909	1,847	6,590,855		10,164,804	(363,814)	(1,454,282)
Cumulative effect of change in accounting principles- equity securities	(16,853)						16,853	(16,853)
Total comprehensive income	1,210,129						1,371,861	(161,732)
Preferred stock cash dividends	(54,390)						(54,390)
Exercise of stock warrants into common stock						$ (7,240)				$ 7,240
Purchases of treasury stock	(1,694,562)								(1,694,562)
Stock-based compensation plans:
Compensation expense, net	25,148		(26)		2,836				22,338
Exercises of stock options, net	56,793				(3,282)				60,075
Stock purchase plan	11,124				2,358				8,766
Directors’ stock plan	1,796				168				1,628
Deferred compensation plans, net, including dividend equivalents	(49)			(131)	(248)		(62)		392
Common stock cash dividends	(370,723)						(370,723)
Ending balance at Sep. 30, 2018	$ 15,436,085	$ 1,231,500	$ 79,883	$ 1,716	$ 6,585,447		$ 11,128,343	$ (542,399)	$ (3,048,405)

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Shareholders' Equity (Unaudited) (Parenthetical) - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Common stock per share dividend amount	$ 2.55	$ 2.25
Retained Earnings [Member]
Common stock per share dividend amount	$ 2.55	$ 2.25
Series A Warrants [Member] | Treasury Stock [Member]
Exercise of warrants into shares of common stock	76,517	304,436
Exercise of warrants into shares of common stock	45,426	165,498

Significant accounting policies

Significant accounting policies	9 Months Ended
	Sep. 30, 2018
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, 2017 (“2017 Annual Report”), except that effective January 1, 2018 the Company adopted amended accounting guidance that is discussed in notes 2, 15 and 16 herein. In the opinion of management, all adjustments necessary for a fair presentation have been made and were all of a normal recurring nature.

Investment securities

Investment securities	9 Months Ended
	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Investment securities	2. Investment securities On January 1, 2018, the Company adopted amended guidance requiring equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in the consolidated statement of income. This amended guidance excludes equity method investments, investments in consolidated subsidiaries, exchange membership ownership interests, and Federal Home Loan Bank of New York and Federal Reserve Bank of New York capital stock. Upon adoption the Company reclassified $17 million, after-tax effect, from accumulated other comprehensive income to retained earnings, representing the difference between fair value and the cost basis of equity investments with readily determinable fair values at January 1, 2018. Net unrealized losses recorded as loss on bank investment securities in the consolidated statement of income during the three months and nine months ended September 30, 2018 were $3 million and $11 million, respectively. 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, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 1,623,860 8 15,196 $ 1,608,672 Obligations of states and political subdivisions 1,792 9 5 1,796 Mortgage-backed securities: Government issued or guaranteed 7,686,746 9,610 283,660 7,412,696 Privately issued 25 — 2 23 Other debt securities 137,552 1,911 8,135 131,328 9,449,975 11,538 306,998 9,154,515 Investment securities held to maturity: U.S. Treasury and federal agencies 445,199 — 412 444,787 Obligations of states and political subdivisions 8,752 32 18 8,766 Mortgage-backed securities: Government issued or guaranteed 2,842,807 1,912 94,241 2,750,478 Privately issued 117,996 11,025 23,747 105,274 Other debt securities 3,965 — — 3,965 3,418,719 12,969 118,418 3,313,270 Total debt securities $ 12,868,694 24,507 425,416 $ 12,467,785 Equity and other securities: Readily marketable equity — at fair value $ 77,871 13,253 995 $ 90,129 Other — at cost 410,518 — — 410,518 Total equity and other securities $ 488,389 13,253 995 $ 500,647 2. Investment securities, continued Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In thousands) December 31, 2017 Investment securities available for sale: U.S. Treasury and federal agencies $ 1,965,665 — 18,178 $ 1,947,487 Obligations of states and political subdivisions 2,555 36 2 2,589 Mortgage-backed securities: Government issued or guaranteed 8,755,482 59,497 98,587 8,716,392 Privately issued 28 — — 28 Other debt securities 136,905 2,402 10,475 128,832 Equity securities 78,161 23,219 424 100,956 10,938,796 85,154 127,666 10,896,284 Investment securities held to maturity: Obligations of states and political subdivisions 24,562 109 49 24,622 Mortgage-backed securities: Government issued or guaranteed 3,187,953 27,236 13,746 3,201,443 Privately issued 135,688 2,574 27,575 110,687 Other debt securities 5,010 — — 5,010 3,353,213 29,919 41,370 3,341,762 Other securities — at cost 415,028 — — 415,028 Total $ 14,707,037 115,073 169,036 $ 14,653,074 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, 2018 and 2017, respectively. At September 30, 2018, 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 $ 1,269,955 1,261,175 Due after one year through five years 361,249 354,788 Due after five years through ten years 101,971 101,055 Due after ten years 30,029 24,778 1,763,204 1,741,796 Mortgage-backed securities available for sale 7,686,771 7,412,719 $ 9,449,975 9,154,515 Debt securities held to maturity: Due in one year or less $ 448,774 448,366 Due after one year through five years 5,177 5,187 Due after ten years 3,965 3,965 457,916 457,518 Mortgage-backed securities held to maturity 2,960,803 2,855,752 $ 3,418,719 3,313,270 2. Investment securities, continued A summary of investment securities that as of September 30, 2018 and December 31, 2017 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, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 9,221 (79 ) 1,601,806 (15,117 ) Obligations of states and political subdivisions 702 (4 ) 375 (1 ) Mortgage-backed securities: Government issued or guaranteed 2,973,861 (80,037 ) 3,628,562 (203,623 ) Privately issued 7 (2 ) — — Other debt securities 15,409 (127 ) 63,639 (8,008 ) 2,999,200 (80,249 ) 5,294,382 (226,749 ) Investment securities held to maturity: U.S. Treasury and federal agencies 444,787 (412 ) — — Obligations of states and political subdivisions 514 (1 ) 3,436 (17 ) Mortgage-backed securities: Government issued or guaranteed 1,762,808 (52,208 ) 800,906 (42,033 ) Privately issued — — 52,180 (23,747 ) 2,208,109 (52,621 ) 856,522 (65,797 ) Total $ 5,207,309 (132,870 ) 6,150,904 (292,546 ) December 31, 2017 Investment securities available for sale: U.S. Treasury and federal agencies $ 278,132 (1,761 ) 1,669,355 (16,417 ) Obligations of states and political subdivisions — — 474 (2 ) Mortgage-backed securities: Government issued or guaranteed 2,106,142 (13,695 ) 3,138,841 (84,892 ) Other debt securities 3,067 (26 ) 61,159 (10,449 ) Equity securities (a) — — 18,162 (424 ) 2,387,341 (15,482 ) 4,887,991 (112,184 ) Investment securities held to maturity: Obligations of states and political subdivisions 2,954 (4 ) 6,110 (45 ) Mortgage-backed securities: Government issued or guaranteed 1,331,759 (7,036 ) 265,695 (6,710 ) Privately issued 5,061 (1,216 ) 55,255 (26,359 ) 1,339,774 (8,256 ) 327,060 (33,114 ) Total $ 3,727,115 (23,738 ) 5,215,051 (145,298 ) (a) Beginning January 1, 2018, equity securities with readily determinable fair values are required to be measured at fair value with changes in fair value recognized in the consolidated statement of income. As a result, subsequent to December 31, 2017 disclosing the time period for which these equity securities had been in a continuous unrealized loss position is no longer relevant. 2. Investment securities, continued The Company owned 1,503 individual debt securities with aggregate gross unrealized losses of $425 million at September 30, 2018. Based on a review of each of the securities in the investment securities portfolio at September 30, 2018, the Company concluded that it expected to recover the amortized cost basis of its investment. As of September 30, 2018, 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, 2018, the Company has not identified events or changes in circumstances which may have a significant adverse effect on the fair value of the $411 million of cost method equity securities.

Loans and leases and the allowa

Loans and leases and the allowance for credit losses	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Loans and leases and the allowance for credit losses	3. Loans and leases and the allowance for credit losses A summary of current, past due and nonaccrual loans as of September 30, 2018 and December 31, 2017 follows: Current 30-89 Days Past Due Accruing Loans Due 90 Days or More (a) Accruing Loans Acquired a Discount Past Due 90 days or More (b) Purchased Impaired (c) Nonaccrual Total (In thousands) September 30, 2018 Commercial, financial, leasing, etc. $ 21,317,925 81,323 1,390 100 — 234,656 $ 21,635,394 Real estate: Commercial 24,650,660 97,630 52,436 4,277 9,948 207,584 25,022,535 Residential builder and developer 1,631,501 7,354 1,656 114 — 2,786 1,643,411 Other commercial construction 6,792,917 39,598 440 16 571 18,887 6,852,429 Residential 13,989,937 437,170 193,604 7,065 224,618 227,619 15,080,013 Residential — limited documentation 2,373,778 93,582 729 — 90,843 82,454 2,641,386 Consumer: Home equity lines and loans 4,850,989 35,212 — 4,694 — 66,303 4,957,198 Automobile 3,527,867 71,184 — — — 20,949 3,620,000 Other 5,144,471 41,992 4,105 27,957 — 9,594 5,228,119 Total $ 84,280,045 905,045 254,360 44,223 325,980 870,832 $ 86,680,485 December 31, 2017 Commercial, financial, leasing, etc. $ 21,332,234 167,756 1,322 327 21 240,991 $ 21,742,651 Real estate: Commercial 24,910,381 166,305 4,444 6,016 16,815 184,982 25,288,943 Residential builder and developer 1,618,973 5,159 — — 1,135 6,451 1,631,718 Other commercial construction 6,407,451 23,467 — — 4,706 10,088 6,445,712 Residential 15,376,759 474,372 233,437 7,582 282,102 235,834 16,610,086 Residential — limited documentation 2,718,019 83,898 — — 105,236 96,105 3,003,258 Consumer: Home equity lines and loans 5,171,345 38,546 — 9,391 — 74,500 5,293,782 Automobile 3,441,371 78,511 — — — 23,781 3,543,663 Other 4,349,071 40,929 5,202 24,102 — 9,866 4,429,170 Total $ 85,325,604 1,078,943 244,405 47,418 410,015 882,598 $ 87,988,983 (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. 3. Loans and leases and the allowance for credit losses, continued One-to-four family residential mortgage loans held for sale were $258 million and $356 million at September 30, 2018 and December 31, 2017, respectively. Commercial real estate loans held for sale were $381 million at September 30, 2018 and $22 million at December 31, 2017. 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, 2018 2017 (In thousands) Outstanding principal balance $ 1,124,232 1,394,188 Carrying amount: Commercial, financial, leasing, etc. 26,473 31,105 Commercial real estate 165,431 228,054 Residential real estate 507,475 620,827 Consumer 97,125 123,413 $ 796,504 1,003,399 Purchased impaired loans included in the table above totaled $326 million at September 30, 2018 and $410 million at December 31, 2017, 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, 2018 and 2017 follows: Three Months Ended September 30 2018 2017 Purchased Other Purchased Other Impaired Acquired Impaired Acquired (In thousands) Balance at beginning of period $ 149,388 $ 117,715 $ 133,532 $ 163,099 Interest income (8,105 ) (18,001 ) (10,815 ) (20,064 ) Reclassifications from nonaccretable balance 8,445 25 30,799 6,041 Other (a) — 2,001 — 1,545 Balance at end of period $ 149,728 101,740 $ 153,516 $ 150,621 Nine Months Ended September 30 2018 2017 Purchased Other Purchased Other Impaired Acquired Impaired Acquired (In thousands) Balance at beginning of period $ 157,918 $ 133,162 $ 154,233 $ 201,153 Interest income (25,893 ) (48,507 ) (32,546 ) (66,505 ) Reclassifications from nonaccretable balance 17,703 11,230 31,829 11,076 Other (a) — 5,855 — 4,897 Balance at end of period $ 149,728 $ 101,740 $ 153,516 150,621 (a) Other changes in expected cash flows including changes in interest rates and prepayment assumptions. 3. Loans and leases and the allowance for credit losses, continued Changes in the allowance for credit losses for the three months ended September 30, 2018 were as follows: Commercial, Financial, Real Estate Leasing, etc. Commercial Residential Consumer Unallocated Total (In thousands) Beginning balance $ 328,830 353,761 76,123 182,987 77,547 $ 1,019,248 Provision for credit losses (6,972 ) (11,394 ) 741 32,887 738 16,000 Net charge-offs Charge-offs (11,792 ) (1,941 ) (3,338 ) (34,995 ) — (52,066 ) Recoveries 7,123 14,577 1,655 12,951 — 36,306 Net (charge-offs) recoveries (4,669 ) 12,636 (1,683 ) (22,044 ) — (15,760 ) Ending balance $ 317,189 355,003 75,181 193,830 78,285 $ 1,019,488 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 nine months ended September 30, 2018 were as follows: Commercial, Financial, Real Estate Leasing, etc. Commercial Residential Consumer Unallocated Total (In thousands) Beginning balance $ 328,599 374,085 65,405 170,809 78,300 $ 1,017,198 Provision for credit losses 11,508 (27,464 ) 16,469 93,502 (15 ) 94,000 Net charge-offs Charge-offs (41,273 ) (7,855 ) (11,658 ) (105,479 ) — (166,265 ) Recoveries 18,355 16,237 4,965 34,998 — 74,555 Net (charge-offs) recoveries (22,918 ) 8,382 (6,693 ) (70,481 ) — (91,710 ) Ending balance $ 317,189 355,003 75,181 193,830 78,285 $ 1,019,488 3. Loans and leases and the allowance for credit losses, continued 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 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 targeted 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 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. 3. Loans and leases and the allowance for credit losses, continued I nformation with respect to loans and leases that were considered impaired as of September 30, 2018 and December 31, 2017 and for the three-month and nine-month periods ended September 30, 2018 and 2017 follows. September 30, 2018 December 31, 2017 Recorded Investment Unpaid Principal Balance Related Allowance Recorded Investment Unpaid Principal Balance Related Allowance (In thousands) With an allowance recorded: Commercial, financial, leasing, etc. $ 171,272 193,161 46,554 177,250 194,257 45,488 Real estate: Commercial 123,451 135,167 11,851 67,199 75,084 9,140 Residential builder and developer 6,248 6,782 352 5,320 5,641 308 Other commercial construction 11,287 11,650 878 4,817 20,357 647 Residential 122,627 145,231 5,695 101,724 122,602 4,000 Residential — limited documentation 75,183 91,149 4,000 77,277 92,439 3,900 Consumer: Home equity lines and loans 48,711 53,869 9,269 48,847 53,914 8,812 Automobile 3,445 4,118 705 13,498 15,737 2,811 Other 11,536 17,010 2,365 3,220 5,872 656 573,760 658,137 81,669 499,152 585,903 75,762 With no related allowance recorded: Commercial, financial, leasing, etc. 84,235 115,654 — 89,126 115,327 — Real estate: Commercial 104,753 114,998 — 138,356 149,716 — Residential builder and developer 1,174 1,174 — 5,057 5,296 — Other commercial construction 7,698 11,428 — 5,456 9,130 — Residential 14,651 19,742 — 13,574 18,980 — Residential — limited documentation 5,873 10,190 — 9,588 16,138 — 218,384 273,186 — 261,157 314,587 — Total: Commercial, financial, leasing, etc. 255,507 308,815 46,554 266,376 309,584 45,488 Real estate: Commercial 228,204 250,165 11,851 205,555 224,800 9,140 Residential builder and developer 7,422 7,956 352 10,377 10,937 308 Other commercial construction 18,985 23,078 878 10,273 29,487 647 Residential 137,278 164,973 5,695 115,298 141,582 4,000 Residential — limited documentation 81,056 101,339 4,000 86,865 108,577 3,900 Consumer: Home equity lines and loans 48,711 53,869 9,269 48,847 53,914 8,812 Automobile 3,445 4,118 705 13,498 15,737 2,811 Other 11,536 17,010 2,365 3,220 5,872 656 Total $ 792,144 931,323 81,669 760,309 900,490 75,762 3. Loans and leases and the allowance for credit losses, continued Three Months Ended September 30, 2018 Three Months Ended September 30, 2017 Interest Income Recognized Interest Income Recognized Average Recorded Investment Total Cash Basis Average Recorded Investment Total Cash Basis (In thousands) Commercial, financial, leasing, etc. $ 256,196 1,985 1,985 $ 224,526 391 391 Real estate: Commercial 204,315 1,489 1,489 233,572 1,425 1,425 Residential builder and developer 9,000 — — 8,550 895 895 Other commercial construction 9,623 3,379 3,379 16,578 25 25 Residential 133,337 1,959 773 113,892 1,903 905 Residential — limited documentation 81,729 1,607 481 91,974 1,624 569 Consumer: Home equity lines and loans 48,542 421 62 47,831 419 99 Automobile 7,805 181 20 14,588 251 22 Other 7,450 126 6 3,269 80 2 Total $ 757,997 11,147 8,195 754,780 7,013 4,333 Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 Interest Income Recognized Interest Income Recognized Average Recorded Investment Total Cash Basis Average Recorded Investment Total Cash Basis (In thousands) Commercial, financial, leasing, etc. $ 266,594 4,101 4,101 242,410 1,674 1,674 Real estate: Commercial 184,795 8,447 8,447 205,814 3,213 3,213 Residential builder and developer 9,111 1,682 1,682 14,551 1,791 1,791 Other commercial construction 9,056 3,438 3,438 15,474 958 958 Residential 126,910 6,190 2,612 108,741 5,004 2,285 Residential — limited documentation 83,700 4,763 1,494 94,680 4,573 1,292 Consumer: Home equity lines and loans 48,661 1,268 220 46,829 1,240 290 Automobile 11,189 630 49 15,483 788 62 Other 4,545 299 12 3,430 227 8 Total $ 744,561 30,818 22,055 747,412 19,468 11,573 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. 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. 3. Loans and leases and the allowance for credit losses, continued 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, 2018 Pass $ 20,498,610 24,190,472 1,499,791 6,709,973 Criticized accrual 902,128 624,479 140,834 123,569 Criticized nonaccrual 234,656 207,584 2,786 18,887 Total $ 21,635,394 25,022,535 1,643,411 6,852,429 December 31, 2017 Pass $ 20,490,486 24,380,184 1,485,148 6,270,812 Criticized accrual 1,011,174 723,777 140,119 164,812 Criticized nonaccrual 240,991 184,982 6,451 10,088 Total $ 21,742,651 25,288,943 1,631,718 6,445,712 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 collectibility 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 $29 million and $23 million, respectively, at September 30, 2018 and $34 million and $25 million, respectively, at December 31, 2017. 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 $18 million and $29 million, respectively, at September 30, 2018 and $20 million and $32 million, respectively, at December 31, 2017. 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 3. Loans and leases and the allowance for credit losses, continued 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. 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, 2018 Individually evaluated for impairment $ 46,554 13,081 9,695 12,339 $ 81,669 Collectively evaluated for impairment 270,635 341,922 50,576 181,491 844,624 Purchased impaired — — 14,910 — 14,910 Allocated $ 317,189 355,003 75,181 193,830 $ 941,203 Unallocated 78,285 Total $ 1,019,488 December 31, 2017 Individually evaluated for impairment $ 45,488 10,095 7,900 12,279 $ 75,762 Collectively evaluated for impairment 283,111 363,990 47,645 158,530 853,276 Purchased impaired — — 9,860 — 9,860 Allocated $ 328,599 374,085 65,405 170,809 938,898 Unallocated 78,300 Total $ 1,017,198 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, 2018 Individually evaluated for impairment $ 255,507 254,611 218,334 63,692 $ 792,144 Collectively evaluated for impairment 21,379,887 33,253,245 17,187,604 13,741,625 85,562,361 Purchased impaired — 10,519 315,461 — 325,980 Total $ 21,635,394 33,518,375 17,721,399 13,805,317 $ 86,680,485 December 31, 2017 Individually evaluated for impairment $ 266,376 226,205 202,163 65,565 $ 760,309 Collectively evaluated for impairment 21,476,254 33,117,512 19,023,843 13,201,050 86,818,659 Purchased impaired 21 22,656 387,338 — 410,015 Total $ 21,742,651 33,366,373 19,613,344 13,266,615 $ 87,988,983 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. 3. Loans and leases and the allowance for credit losses, continued The table that follows summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the three-month and nine-month periods ended September 30, 2018 and 2017: Post-modification (a) Number Pre- modification Recorded Investment Principal Deferral Interest Rate Reduction Other Combination of Concession Types Total Three Months Ended September 30, 2018 (Dollars in thousands) Commercial, financial, leasing, etc. 47 $ 6,837 $ 1,683 $ 5 $ — $ 5,018 $ 6,706 Real estate: Commercial 18 11,581 1,493 — 3,475 6,297 11,265 Residential 34 8,182 6,026 — — 3,002 9,028 Residential — limited documentation 3 716 — — — 847 847 Consumer: Home equity lines and loans 17 1,651 220 — — 1,450 1,670 Automobile 30 526 526 — — — 526 Other 2 44 44 — — — 44 Total 151 $ 29,537 $ 9,992 $ 5 $ 3,475 $ 16,614 $ 30,086 Three Months Ended September 30, 2017 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 3. Loans and leases and the allowance for credit losses, continued Post-modification (a) Nine Months Ended September 30, 2018 Number Pre- modification Recorded Investment Principal Deferral Interest Rate Reduction Other Combination of Concession Types Total (Dollars in thousands) Commercial, financial, leasing, etc. 150 $ 96,221 $ 47,029 $ 658 $ 6,111 $ 43,086 $ 96,884 Real estate: Commercial 66 25,561 14,693 175 3,869 7,224 25,961 Other commercial construction 1 752 746 — — — 746 Residential 111 28,769 15,785 — — 15,670 31,455 Residential — limited documentation 8 1,595 467 — — 1,423 1,890 Consumer: Home equity lines and loans 41 3,554 224 — — 3,357 3,581 Automobile 57 1,007 995 — — 12 1,007 Other 4 93 93 — — — 93 Total 438 $ 157,552 $ 80,032 $ 833 $ 9,980 $ 70,772 $ 161,617 Nine Months Ended September 30, 2017 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 (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, 2018 and 2017 and for which there was a subsequent payment default during the nine-month periods ended September 30, 2018 and 2017, respectively, were not material. The amount of foreclosed residential real estate property held by the Company was $85 million and $108 million at September 30, 2018 and December 31, 2017, respectively. There were $404 million and $497 million at September 30, 2018 and December 31, 2017, 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, 2018, approximately 40% were classified as purchased impaired and 20% were government guaranteed.

Borrowings

Borrowings	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Borrowings	4. Borrowings During January 2018, M&T Bank, the principal subsidiary of M&T, issued $1.0 billion of senior notes that mature in January 2021 pursuant to a Bank Note Program, of which $650 million have a 2.625% fixed interest rate and $350 million have a variable rate paid quarterly at rates that are indexed to the three-month London Interbank Offered Rate (“LIBOR”). In July 2018, M&T issued $750 million of senior notes that mature in July 2023, of which $500 million have a 3.55% fixed interest rate and $250 million have a variable rate paid quarterly at rates that are indexed to the three-month LIBOR. M&T had $521 million of fixed and variable rate junior subordinated deferrable interest debentures ("Junior Subordinated Debentures") outstanding at September 30, 2018 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. Also included in long-term borrowings are agreements to repurchase securities of $412 million and $422 million at September 30, 2018 and December 31, 2017, 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 $429 million and $442 million at September 30, 2018 and December 31, 2017, respectively .

Shareholders' equity

Shareholders' equity	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Shareholders' equity	5. 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, 2018 and December 31, 2017 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 $73.58 per share issued in connection with the Series A preferred stock expire on December 23, 2018 and totaled 180,491 at September 30, 2018. (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. 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 95,743 shares of M&T common stock at $517.01 per share was outstanding at September 30, 2018. The obligation under that warrant was assumed by M&T in an acquisition and expires on December 12, 2018.

Pension plans and other postret

Pension plans and other postretirement benefits	9 Months Ended
	Sep. 30, 2018
Compensation And Retirement Disclosure [Abstract]
Pension plans and other postretirement benefits	6. 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 2018 2017 2018 2017 (In thousands) Service cost $ 5,086 5,048 234 293 Interest cost on projected benefit obligation 18,676 19,818 573 929 Expected return on plan assets (30,781 ) (27,131 ) — — Amortization of prior service cost (credit) 139 139 (1,182 ) (340 ) Amortization of net actuarial loss (gain) 10,948 7,316 (206 ) (247 ) Net periodic benefit cost $ 4,068 5,190 (581 ) 635 Pension Benefits Other Postretirement Benefits Nine Months Ended September 30 2018 2017 2018 2017 (In thousands) Service cost $ 15,258 15,145 703 878 Interest cost on projected benefit obligation 56,029 59,452 1,719 2,787 Expected return on plan assets (92,344 ) (81,393 ) — — Amortization of prior service cost (credit) 417 418 (3,546 ) (1,019 ) Amortization of net actuarial loss (gain) 32,844 21,947 (619 ) (741 ) Net periodic benefit cost $ 12,204 15,569 (1,743 ) 1,905 Service cost is reflected in salaries and employee benefits expense. The other components of net periodic benefit cost are reflected in other costs of operations. Expenses incurred in connection with the Company's defined contribution pension and retirement savings plans totaled $16,907,000 and $16,085,000 for the three months ended September 30, 2018 and 2017, respectively, and $55,375,000 and $53,127,000 for the nine months ended September 30, 2018 and 2017, respectively, and are included in salaries and employee benefits expense.

Earnings per common share

Earnings per common share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings per common share	7. Earnings per common share The computations of basic earnings per common share follow: Three Months Ended September 30 Nine Months Ended September 30 2018 2017 2018 2017 (In thousands, except per share) Income available to common shareholders: Net income $ 526,091 355,923 1,371,861 1,085,903 Less: Preferred stock dividends (a) (18,130 ) (18,130 ) (54,390 ) (54,604 ) Net income available to common equity 507,961 337,793 1,317,471 1,031,299 Less: Income attributable to unvested stock-based compensation awards (2,598 ) (1,992 ) (6,774 ) (6,288 ) Net income available to common shareholders $ 505,363 335,801 1,310,697 1,025,011 Weighted-average shares outstanding: Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards 143,556 152,245 146,177 153,814 Less: Unvested stock-based compensation awards (734 ) (898 ) (753 ) (948 ) Weighted-average shares outstanding 142,822 151,347 145,424 152,866 Basic earnings per common share $ 3.54 2.22 9.01 6.71 (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 2018 2017 2018 2017 (In thousands, except per share) Net income available to common equity $ 507,961 337,793 1,317,471 1,031,299 Less: Income attributable to unvested stock-based compensation awards (2,596 ) (1,989 ) (6,768 ) (6,276 ) Net income available to common shareholders $ 505,365 335,804 1,310,703 1,025,023 Adjusted weighted-average shares outstanding: Common and unvested stock-based compensation awards 143,556 152,245 146,177 153,814 Less: Unvested stock-based compensation awards (734 ) (898 ) (753 ) (948 ) Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock 154 344 181 427 Adjusted weighted-average shares outstanding 142,976 151,691 145,605 153,293 Diluted earnings per common share $ 3.53 2.21 9.00 6.69 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 212,407 and 408,657 common shares during the three-month periods ended September 30, 2018 and 2017, respectively, and 220,653 and 404,487 common shares during the nine-month periods ended September 30, 2018 and 2017, 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

Comprehensive income	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Comprehensive income	8. 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 Defined Benefit Total Amount Income Securities (a) Plans Other Before Tax Tax Net (In thousands) Balance — January 1, 2018 $ (59,957 ) (413,168 ) (20,165 ) $ (493,290 ) 129,476 $ (363,814 ) Cumulative effect of change in accounting principle — equity securities (22,795 ) — — (22,795 ) 5,942 (16,853 ) Other comprehensive income before reclassifications: Unrealized holding losses, net (230,135 ) — — (230,135 ) 60,494 (169,641 ) Foreign currency translation adjustment — — (1,783 ) (1,783 ) 374 (1,409 ) Unrealized losses on cash flow hedges — — (26,522 ) (26,522 ) 6,972 (19,550 ) Total other comprehensive income (loss) before reclassifications (230,135 ) — (28,305 ) (258,440 ) 67,840 (190,600 ) Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income: Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities 2,519 — — 2,519 (c) (662 ) 1,857 Gains realized in net income (18 ) — — (18 ) (d) 4 (14 ) Accretion of net gain on terminated cash flow hedges — — (83 ) (83 ) (e) 22 (61 ) Net yield adjustment from cash flow hedges currently in effect — — 7,650 7,650 (e) (2,011 ) 5,639 Amortization of prior service credit — (3,129 ) — (3,129 ) (f) 823 (2,306 ) Amortization of actuarial losses — 32,225 — 32,225 (f) (8,472 ) 23,753 Total other comprehensive income (loss) (227,634 ) 29,096 (20,738 ) (219,276 ) 57,544 (161,732 ) Balance — September 30, 2018 $ (310,386 ) (384,072 ) (40,903 ) $ (735,361 ) 192,962 $ (542,399 ) Investment Securities Defined Benefit Total Amount Income With OTTI (b) 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 HTM securities — 2,535 — — 2,535 (c) (998 ) 1,537 (Gains) losses realized in net income (50 ) 67 — — 17 (d) (7 ) 10 Accretion of net gain on terminated cash flow hedges — — — (109 ) (109 ) (e) 43 (66 ) Net yield adjustment from cash flow hedges currently in effect — — — (2,275 ) (2,275 ) (e) 895 (1,380 ) Amortization of prior service credit — — (601 ) — (601 ) (f) 236 (365 ) Amortization of actuarial losses — — 21,206 — 21,206 (f) (8,345 ) 12,861 Total other comprehensive income (loss) (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 ) (a) Beginning January 1, 2018, equity securities with readily determinable fair values are required to be measured at fair value with changes in fair value recognized in the income statement. Separate presentation of investment securities with an other-than-temporary impairment charge is no longer required. (b) Other-than-temporary impairment (c) Included in interest income (d) Included in gain (loss) on bank investment securities (e) Included in interest expense (f) Included in other costs of operations 8. Comprehensive income, continued Accumulated other comprehensive income (loss), net consisted of the following: Investment Defined Benefit Securities Plans Other Total (In thousands) Balance — December 31, 2017 $ (44,150 ) (304,546 ) (15,118 ) $ (363,814 ) Cumulative effect of change in accounting principle — equity securities (16,853 ) — — (16,853 ) Net gain (loss) during period (167,798 ) 21,447 (15,381 ) (161,732 ) Balance — September 30, 2018 $ (228,801 ) (283,099 ) (30,499 ) $ (542,399 )

Derivative financial instrument

Derivative financial instruments	9 Months Ended
	Sep. 30, 2018
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative financial instruments	9. 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, 2018. The net effect of interest rate swap agreements was to decrease net interest income by $8 million and $12 million for the three-month and nine-month periods ended September 30, 2018, respectively, compared with increases of $7 million and $18 million for the three-month and nine-month periods ended September 30, 2017, respectively. 9. Derivative financial instruments, continued 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: Notional Average Weighted- Average Rate Estimated Fair Amount Maturity Fixed Variable Value (In thousands) (In years) (In thousands) September 30, 2018 Fair value hedges: Fixed rate long-term borrowings (b) $ 5,200,000 2.7 2.45 % 2.76 % $ 1,458 Cash flow hedges: Interest payments on variable rate commercial real estate loans (b)(c) 10,550,000 1.4 1.52 % 2.11 % 988 Total $ 15,750,000 1.8 $ 2,446 December 31, 2017 Fair value hedges: Fixed rate long-term borrowings (b) $ 4,550,000 2.9 2.27 % 2.09 % $ 573 Cash flow hedges: Interest payments on variable rate commercial real estate loans (b)(d) 4,850,000 2.0 1.52 % 1.36 % 66 Total $ 9,400,000 2.5 $ 639 (a) Certain clearinghouse exchanges consider payments by counterparties for variation margin on derivative instruments to be settlements of those positions. The impact of such treatment at September 30, 2018 and December 31, 2017 was a reduction of the estimated fair value losses on interest rate swap agreements designated as fair value hedges of $110.3 million and $41.1 million, respectively, and on interest rate swap agreements designated as cash flow hedges of $36.1 million and $16.3 million, respectively. (b) Under the terms of these agreements, the Company receives settlement amounts at a fixed rate and pays at a variable rate. (c) (d) 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 $40.3 billion and $29.9 billion at September 30, 2018 and December 31, 2017, respectively. The notional amounts of foreign currency and other option and futures contracts entered into for trading account purposes aggregated $869 million and $530 million at September 30, 2018 and December 31, 2017, respectively. 9. Derivative financial instruments, continued 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, December 31, September 30, December 31, 2018 2017 2018 2017 (In thousands) Derivatives designated and qualifying as hedging instruments Interest rate swap agreements (a) $ 2,446 $ 639 $ — $ — Commitments to sell real estate loans (a) 5,832 734 546 283 8,278 1,373 546 283 Derivatives not designated and qualifying as hedging instruments Mortgage-related commitments to originate real estate loans for sale (a) 5,625 8,797 1,439 494 Commitments to sell real estate loans (a) 5,795 2,526 250 1,019 Trading: Interest rate contracts (b) 62,472 74,164 299,791 132,104 Foreign exchange and other option and futures contracts (b) 9,270 5,657 8,942 5,286 83,162 91,144 310,422 138,903 Total derivatives $ 91,440 $ 92,517 $ 310,968 $ 139,186 (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 variation margin payments at September 30, 2018 and December 31, 2017 Amount of Gain (Loss) Recognized Three Months Ended September 30, 2018 Three Months Ended September 30, 2017 Derivative Hedged Item Derivative Hedged Item (In thousands) Derivatives in fair value hedging relationships Interest rate swap agreements: Fixed rate long-term borrowings (a) $ (12,568 ) 12,607 $ (13,509 ) 14,026 Derivatives not designated as hedging instruments Trading: Interest rate contracts (b) $ (1,348 ) $ (418 ) Foreign exchange and other option and futures contracts (b) 782 1,362 Total $ (566 ) $ 944 9. Derivative financial instruments, continued Amount of Gain (Loss) Recognized Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 Derivative Hedged Item Derivative Hedged Item (In thousands) Derivatives in fair value hedging relationships Interest rate swap agreements: Fixed rate long-term borrowings (a) $ (68,315 ) 68,861 $ (23,423 ) 23,049 Derivatives not designated as hedging instruments Trading: Interest rate contracts (b) $ (5,639 ) $ 2,363 Foreign exchange and other option and futures contracts (b) 5,778 4,766 Total $ 139 $ 7,129 (a) Effective January 1, 2018, reported as an adjustment to interest expense. Prior to 2018, reported as other revenues from operations. (b) Reported as trading account and foreign exchange gains. Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount of the Hedged Item September 30, December 31, September 30, December 31, 2018 2017 2018 2017 (In thousands) Location in the Consolidated Balance Sheet of the Hedged Items in Fair Value Hedges Long-term debt $ 5,085,610 $ 4,504,029 $ (108,994 ) $ (40,133 ) The amount of gain (loss) resulting from hedge ineffectiveness recognized in the consolidated statement of income associated with derivatives designated as cash flow hedges was not material during the three months and nine months ended September 30, 2018 and 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 $18 million and $16 million at September 30, 2018 and December 31, 2017, 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. 9. Derivative financial instruments, continued The aggregate fair value of derivative financial instruments in a liability position and the net liability positions with counterparties, which are subject to enforceable master netting arrangements, was $3 million and $13 million at September 30, 2018 and December 31, 2017, respectively. The Company was required to post collateral relating to those positions of $3 million and $12 million at September 30, 2018 and December 31, 2017, 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, 2018 was not significant. If the credit risk-related contingent features had been triggered on September 30, 2018, the Company would not have been required to post any additional collateral to counterparties. The aggregate fair value of derivative financial instruments in an asset position and the net asset positions with counterparties, which are subject to enforceable master netting arrangements, was $49 million and $13 million at September 30, 2018 and December 31, 2017, respectively. Counterparties posted collateral relating to those positions of $46 million and $12 million at September 30, 2018 and December 31, 2017, 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 $48 million and $52 million at September 30, 2018 and December 31, 2017, respectively. The fair value asset and liability amounts of derivative contracts at September 30, 2018 have been reduced by variation margin payments treated as settlements of $302 million and $149 million, respectively. Variation margin on derivative contracts not treated as settlements continues to represent collateral posted or received by the Company.

Variable interest entities and

Variable interest entities and asset securitizations	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Variable interest entities and asset securitizations	10. Variable interest entities and asset securitizations The Company’s securitization activity has consisted of securitizing loans originated for sale into government issued or guaranteed mortgage-backed securities. The amounts of those securitizations during the nine-month periods ended September 30, 2018 and 2017 are presented in the Company’s consolidated statement of cash flows. The Company has not recognized any losses as a result of having securitized assets. As described in note 4, 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 each of September 30, 2018 and December 31, 2017, the Company included the junior subordinated debentures as “long-term borrowings” in its consolidated balance sheet and recognized $23 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 4. The Company has invested as a limited partner in various partnerships that collectively had total assets of approximately $1.0 billion at each of September 30, 2018 and December 31, 2017. 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 10. Variable interest entities and asset securitizations, continued 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 $457 million, including $215 million of unfunded commitments, at September 30, 2018 and $420 million, including $201 million of unfunded commitments, at December 31, 2017. Contingent commitments to provide additional capital contributions to these partnerships were not material at September 30, 2018. 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 $13 million and $39 million of its investments in qualified affordable housing projects to income tax expense during the three-month and nine-month periods ended September 30, 2018, respectively, and recognized $15 million and $47 million of tax credits and other tax benefits during each of those respective periods. Similarly, for the three-month and nine-month periods ended September 30, 2017, the Company amortized $11 million and $35 million, respectively, of its investments in qualified affordable housing projects to income tax expense and recognized $16 million and $47 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

Fair value measurements	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair value measurements	11. 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, 2018. 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 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. 11. Fair value measurements, continued Trading account assets and liabilities Trading account assets and liabilities consist primarily of interest rate contracts 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 and equity securities 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 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. 11. Fair value measurements, continued The following tables present assets and liabilities at September 30, 2018 and December 31, 2017 measured at estimated fair value on a recurring basis: Fair Value Measurements Level 1 (a) Level 2 (a) Level 3 (In thousands) September 30, 2018 Trading account assets $ 125,038 $ 47,653 $ 77,385 $ — Investment securities available for sale: U.S. Treasury and federal agencies 1,608,672 — 1,608,672 — Obligations of states and political subdivisions 1,796 — 1,796 — Mortgage-backed securities: Government issued or guaranteed 7,412,696 — 7,412,696 — Privately issued 23 — — 23 Other debt securities 131,328 — 131,328 — 9,154,515 — 9,154,492 23 Equity securities 90,129 72,651 17,478 — Real estate loans held for sale 638,579 — 638,579 — Other assets (b) 19,698 — 14,073 5,625 Total assets $ 10,027,959 $ 120,304 $ 9,902,007 $ 5,648 Trading account liabilities $ 308,733 $ — $ 308,733 $ — Other liabilities (b) 2,235 — 796 1,439 Total liabilities $ 310,968 $ — $ 309,529 $ 1,439 December 31, 2017 Trading account assets $ 132,909 $ 47,873 $ 85,036 $ — Investment securities available for sale: U.S. Treasury and federal agencies 1,947,487 — 1,947,487 — Obligations of states and political subdivisions 2,589 — 2,589 — Mortgage-backed securities: Government issued or guaranteed 8,716,392 — 8,716,392 — Privately issued 28 — — 28 Other debt securities 128,832 — 128,832 — Equity securities 100,956 73,232 27,724 — 10,896,284 73,232 10,823,024 28 Real estate loans held for sale 378,047 — 378,047 — Other assets (b) 12,696 — 3,899 8,797 Total assets $ 11,419,936 $ 121,105 $ 11,290,006 $ 8,825 Trading account liabilities $ 137,390 $ — $ 137,390 $ — Other liabilities (b) 1,796 — 1,302 494 Total liabilities $ 139,186 $ — $ 138,692 $ 494 (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, 2017. (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). 11. 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, 2018 were as follows: Investment Securities Available for S Privately Issued Mortgage-Backed Securities Other Assets and Other Liabilities (In thousands) Balance — June 30, 2018 $ 24 10,751 Total gains (losses) realized/unrealized: Included in earnings — 10,284 (b) Settlements (1 ) — Transfers out of Level 3 (a) — (16,849 ) (c) Balance — September 30, 2018 $ 23 4,186 Changes in unrealized gains included in earnings related to assets still held at September 30, 2018 $ — 4,508 (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, 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 out of Level 3 (a) — (21,016 ) (c) 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) 11. 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, 2018 were as follows: Investment securities available for sale Privately Issued Mortgage-Backed Securities Other Assets and Other Liabilities (In thousands) Balance — January 1, 2018 $ 28 8,303 Total gains (losses) realized/unrealized: Included in earnings — 38,691 (b) Settlements (5 ) — Transfers out of Level 3 (a) — (42,808 ) (c) Balance — September 30, 2018 $ 23 4,186 Changes in unrealized gains included in earnings related to assets still held at September 30, 2018 $ — 3,663 (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, 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 out of Level 3 (a) — (59,427 ) (c) 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) (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) Transfers out of Level 3 consist of interest rate locks transferred to closed loans. 11. 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, 2018. 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 $292 million at September 30, 2018 ($128 million and $164 million of which were classified as Level 2 and Level 3, respectively), $210 million at December 31, 2017 ($145 million and $65 million of which were classified as Level 2 and Level 3, respectively) and $184 million at September 30, 2017 ($105 million and $79 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, 2018 were decreases of $35 million and $69 million for the three-month and nine-month periods ended September 30, 2018, 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. 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 $32 million and $36 million at September 30, 2018 and 2017, 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, 2018 and 2017. 11. 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, 2018 and December 31, 2017: Fair Value Valuation Technique Unobservable Inputs/Assumptions Range (Weighted- Average) (In thousands) September 30, 2018 Recurring fair value measurements Privately issued mortgage-backed securities $ 23 Two independent pricing quotes — — Net other assets (liabilities) (a) 4,186 Discounted cash flow Commitment expirations 0%-90% (16%) December 31, 2017 Recurring fair value measurements Privately issued mortgage-backed securities $ 28 Two independent pricing quotes — — Net other assets (liabilities) (a) 8,303 Discounted cash flow Commitment expirations 0%-78% (22%) (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. 11. 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, 2018 Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 (In thousands) Financial assets: Cash and cash equivalents $ 1,311,611 1,311,611 1,232,393 79,218 — Interest-bearing deposits at banks 6,523,746 6,523,746 — 6,523,746 — Trading account assets 125,038 125,038 47,653 77,385 — Investment securities 13,073,881 12,968,432 72,651 12,790,484 105,297 Loans and leases: Commercial loans and leases 21,635,394 21,215,945 — — 21,215,945 Commercial real estate loans 33,518,375 32,971,832 — 381,007 32,590,825 Residential real estate loans 17,721,399 17,429,777 — 3,984,387 13,445,390 Consumer loans 13,805,317 13,676,356 — — 13,676,356 Allowance for credit losses (1,019,488 ) — — — — Loans and leases, net 85,660,997 85,293,910 — 4,365,394 80,928,516 Accrued interest receivable 349,903 349,903 — 349,903 — Financial liabilities: Noninterest-bearing deposits $ (31,773,560 ) (31,773,560 ) — (31,773,560 ) — Savings and interest-checking deposits (51,108,962 ) (51,108,962 ) — (51,108,962 ) — Time deposits (5,810,587 ) (5,872,516 ) — (5,872,516 ) — Deposits at Cayman Islands office (447,287 ) (447,287 ) — (447,287 ) — Short-term borrowings (1,310,110 ) (1,310,110 ) — (1,310,110 ) — Long-term borrowings (9,140,268 ) (9,160,009 ) — (9,160,009 ) — Accrued interest payable (68,196 ) (68,196 ) — (68,196 ) — Trading account liabilities (308,733 ) (308,733 ) — (308,733 ) — Other financial instruments: Commitments to originate real estate loans for sale $ 4,186 4,186 — — 4,186 Commitments to sell real estate loans 10,831 10,831 — 10,831 — Other credit-related commitments (129,102 ) (129,102 ) — — (129,102 ) Interest rate swap agreements used for interest rate risk management 2,446 2,446 — 2,446 — 11. Fair value measurements, continued December 31, 2017 Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 (In thousands) Financial assets: Cash and cash equivalents $ 1,420,888 1,420,888 1,352,035 68,853 — Interest-bearing deposits at banks 5,078,903 5,078,903 — 5,078,903 — Trading account assets 132,909 132,909 47,873 85,036 — Investment securities 14,664,525 14,653,074 73,232 14,469,127 110,715 Loans and leases: Commercial loans and leases 21,742,651 21,321,282 — — 21,321,282 Commercial real estate loans 33,366,373 32,950,724 — 22,130 32,928,594 Residential real estate loans 19,613,344 19,596,826 — 4,440,645 15,156,181 Consumer loans 13,266,615 13,161,517 — — 13,161,517 Allowance for credit losses (1,017,198 ) — — — — Loans and leases, net 86,971,785 87,030,349 — 4,462,775 82,567,574 Accrued interest receivable 327,170 327,170 — 327,170 — Financial liabilities: Noninterest-bearing deposits $ (33,975,180 ) (33,975,180 ) — (33,975,180 ) — Savings and interest-checking deposits (51,698,008 ) (51,698,008 ) — (51,698,008 ) — Time deposits (6,580,962 ) (6,635,048 ) — (6,635,048 ) — Deposits at Cayman Islands office (177,996 ) (177,996 ) — (177,996 ) — Short-term borrowings (175,099 ) (175,099 ) — (175,099 ) — Long-term borrowings (8,141,430 ) (8,193,783 ) — (8,193,783 ) — Accrued interest payable (75,641 ) (75,641 ) — (75,641 ) — Trading account liabilities (137,390 ) (137,390 ) — (137,390 ) — Other financial instruments: Commitments to originate real estate loans for sale $ 8,303 8,303 — — 8,303 Commitments to sell real estate loans 1,958 1,958 — 1,958 — Other credit-related commitments (125,281 ) (125,281 ) — — (125,281 ) Interest rate swap agreements used for interest rate risk management 639 639 — 639 — 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 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.

Commitments and contingencies

Commitments and contingencies	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and contingencies	12. 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, 2018 2017 (In thousands) Commitments to extend credit Home equity lines of credit $ 5,465,893 5,482,622 Commercial real estate loans to be sold 153,900 194,763 Other commercial real estate 6,549,168 6,050,569 Residential real estate loans to be sold 307,955 347,113 Other residential real estate 267,948 201,426 Commercial and other 14,608,286 12,733,815 Standby letters of credit 2,385,904 2,497,844 Commercial letters of credit 42,030 46,739 Financial guarantees and indemnification contracts 3,416,625 3,434,381 Commitments to sell real estate loans 994,879 812,217 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 $3.3 billion at each of September 30, 2018 and December 31, 2017. 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. 12. Commitments and contingencies, continued 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, 2018 the Company believes that its obligation to loan purchasers was not material to the Company’s consolidated financial position. As previously disclosed, Wilmington Trust Corporation (“WTC”), a wholly-owned subsidiary of M&T, is the subject of a class action lawsuit alleging that WTC’s financial reporting and securities filings prior to its acquisition by M&T in 2011 were in violation of securities laws. In April 2018, the parties reached an agreement in principle and a formal settlement agreement was executed and filed with the court later in the second quarter of 2018. The proposed settlement was preliminarily approved by the court in July 2018. In the first quarter of 2018, the Company increased its reserve for litigation matters by $135 million in anticipation of the settlement. The settlement amount of $200 million was paid, pursuant to the settlement agreement, during the third quarter of 2018. The settlement agreement is subject to the final approval of the court which is expected to occur in the fourth quarter of 2018. M&T and its subsidiaries are subject in the normal course of business to various other pending and threatened legal proceedings and 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

Segment information	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Segment information	13. 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 2017 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. 13. Segment information, continued Information about the Company's segments is presented in the following table: Three Months Ended September 30 2018 2017 Total Revenues(a) Inter- segment Revenues Net Income (Loss) Total Revenues(a) Inter- segment Revenues Net Income (Loss) (In thousands) Business Banking $ 138,898 920 43,730 $ 130,501 919 31,408 Commercial Banking 280,671 875 147,910 267,822 840 109,797 Commercial Real Estate 214,266 371 116,386 212,014 401 97,295 Discretionary Portfolio 53,061 (10,270 ) 39,723 65,808 (12,346 ) 31,515 Residential 79,603 15,402 13,289 90,018 18,866 13,546 Retail Banking 427,452 2,862 141,612 392,542 2,668 96,329 All Other 294,381 (10,160 ) 23,441 257,858 (11,348 ) (23,967 ) Total $ 1,488,332 — 526,091 $ 1,416,563 — 355,923 Nine Months Ended September 30 2018 2017 Total Revenues(a) Inter- segment Revenues Net Income (Loss) Total Revenues(a) Inter- segment Revenues Net Income (Loss) (In thousands) Business Banking $ 402,811 2,750 124,455 $ 375,816 2,836 85,146 Commercial Banking 816,566 2,653 399,766 818,846 2,603 328,211 Commercial Real Estate 622,414 1,096 337,380 604,437 1,165 269,113 Discretionary Portfolio 162,075 (31,656 ) 88,575 216,798 (37,670 ) 95,200 Residential Mortgage Banking 244,228 46,870 43,637 264,120 55,221 37,206 Retail Banking 1,241,468 8,434 408,081 1,144,964 8,760 282,614 All Other 899,184 (30,147 ) (30,033 ) 751,703 (32,915 ) (11,587 ) Total $ 4,388,746 — 1,371,861 $ 4,176,684 — 1,085,903 13. Segment information, continued Average Total Assets Nine Months Ended September 30 Year Ended December 31 2018 2017 2017 (In millions) Business Banking $ 5,637 5,596 5,602 Commercial Banking 26,524 26,699 26,573 Commercial Real Estate 22,899 22,800 22,741 Discretionary Portfolio 32,659 37,807 37,203 Residential Mortgage Banking 2,123 2,335 2,355 Retail Banking 13,522 12,519 12,702 All Other 13,312 13,317 13,684 Total $ 116,676 121,073 120,860 (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 $5,733,000 and $8,828,000 for the three-month periods ended September 30, 2018 and 2017, respectively, and $15,939,000 and $25,563,000 for the nine-month periods ended September 30, 2018 and 2017, 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 Lendi

Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P.	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P.	14. 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 Bayview Financial Holdings, L.P. (together with its affiliates, "Bayview Financial"), a privately-held specialty 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 $2.7 billion and $3.0 billion at September 30, 2018 and December 31, 2017, respectively. Revenues from those servicing rights were $4 million for each of the three-month periods ended September 30, 2018 and 2017, and $11 million and $13 million for the nine-month periods ended September 30, 2018 and 2017, respectively. The Company sub-services residential mortgage loans for Bayview Financial having outstanding principal balances of $60.3 billion and $56.6 billion at September 30, 2018 and December 31, 2017, respectively. Revenues earned for sub-servicing loans for Bayview Financial were $28 million and $26 million for the three-month periods ended September 30, 2018 and 2017, respectively, and $86 million and $74 million for the nine-month periods ended September 30, 2018 and 2017, respectively. In addition, the Company held $118 million and $136 million of mortgage-backed securities in its held-to-maturity portfolio at September 30, 2018 and December 31, 2017, respectively, that were securitized by Bayview Financial. At September 30, 2018, the Company held $90 million of Bayview Financial’s $750 million syndicated loan facility.

Revenue from Contracts with Cus

Revenue from Contracts with Customer	9 Months Ended
	Sep. 30, 2018
Revenue From Contract With Customer [Abstract]
Revenue from Contracts with Customer	15. Revenue from contracts with customers Effective January 1, 2018 the Company adopted amended accounting and disclosure guidance for revenue from contracts with customers under the modified retrospective approach. A significant amount of the Company’s revenues are derived from net interest income on financial assets and liabilities, mortgage banking revenues, trading account and foreign exchange gains, investment securities gains, loan and letter of credit fees, operating lease income, income from bank-owned life insurance, and certain other revenues that are generally excluded from the scope of the amended guidance. As of result of the adoption, the Company began reporting credit card interchange revenue net of $3 million and $9 million of rewards in other revenue from operations for the three-month and nine-month periods ended September 30, 2018, respectively. For the three-month and nine-month periods ended September 30, 2017, credit card rewards expense of $3 million and $8 million, respectively, was included in other costs of operations. The adjustment to beginning retained earnings as well as the impact of any changes in timing of revenue recognition of noninterest income items within the scope of the guidance was not material to the Company’s consolidated financial position at December 31, 2017 or its consolidated results of operations for the nine months ended September 30, 2018. For noninterest income revenue streams within the scope of the amended guidance, the Company recognizes the expected amount of consideration as revenue when the performance obligations related to the services under the terms of a contract are satisfied. The Company’s contracts generally do not contain terms that necessitate significant judgment to determine the amount of revenue to recognize. The Company generally charges customer accounts or otherwise bills customers upon completion of its services. Typically the Company’s contracts with customers have a duration of one year or less and payment for services is received at least annually, but oftentimes more frequently as services are provided. At September 30, 2018, the Company had $52 million of uncollected amounts receivable related to recognized revenue from the sources in the table below. Such amount is classified in accrued interest and other assets in the Company’s consolidated balance sheet. In certain situations the Company is paid in advance of providing services and defers the recognition of revenue until its service obligation is satisfied. At September 30, 2018, the Company had deferred revenue of $43 million related to the sources in the table below recorded in accrued interest and other liabilities on its consolidated balance sheet. The following tables summarize sources of M&T’s noninterest income during 2018 that are subject to the amended guidance. Three Months Ended September 30, 2018 Business Banking Commercial Banking Commercial Real Estate Discretionary Portfolio Residential Mortgage Banking Retail Banking All Other Total (In thousands) Classification in consolidated statement of income Service charges on deposit accounts $ 15,767 24,167 2,374 — 2 64,709 1,628 $ 108,647 Trust income — — — — — — 133,545 133,545 Brokerage services income — — — — — — 12,267 12,267 Other revenues from operations: Merchant discount and credit card fees 9,238 13,520 643 — — 3,908 462 27,771 Other — 1,662 1,822 386 916 9,397 6,723 20,906 $ 25,005 39,349 4,839 386 918 78,014 154,625 $ 303,136 15. Revenue from contracts with customers, continued Nine Months Ended September 30, 2018 Business Banking Commercial Banking Commercial Real Estate Discretionary Portfolio Residential Mortgage Banking Retail Banking All Other Total (In thousands) Classification in consolidated statement of income Service charges on deposit accounts $ 46,782 73,091 7,589 — 8 188,325 4,751 $ 320,546 Trust income — — — — — — 402,561 402,561 Brokerage services income — — — — — — 38,288 38,288 Other revenues from operations: Merchant discount and credit card fees 25,075 38,774 1,625 — — 11,436 1,695 78,605 Other — 6,871 4,896 1,251 2,886 28,875 23,429 68,208 $ 71,857 118,736 14,110 1,251 2,894 228,636 470,724 $ 908,208 Service charges on deposit accounts are generally deducted directly from customer account balances and include account maintenance charges as well as fees for insufficient funds, debit card usage, and other transactional services. Account maintenance charges are generally recognized as revenue on a monthly basis, whereas transactional fees are recognized after M&T provides the respective service. Trust income includes fees related to the Institutional Client Services (“ICS”) business and the Wealth Advisory Services (“WAS”) business. Revenues from the ICS business are largely derived from a variety of trustee, agency, investment, cash management and administrative services, whereas revenues from the WAS business are mainly derived from asset management, fiduciary services, and family office services. Trust fees may be billed in arrears or in advance and are recognized as revenues as M&T’s performance obligations are satisfied. Certain fees are based on a percentage of assets invested or under management and are recognized as the service is performed and constraints regarding the uncertainty of the amount of fees are resolved. Brokerage service income includes revenues from the sale of mutual funds and annuities and securities brokerage fees. Such revenues are generally recognized at the time of transaction execution. Mutual fund and other distribution fees are recognized upon initial placement of customer funds as well as in future periods as such customers continue to hold amounts in those mutual funds. Other revenues from operations include merchant discount and credit card fees such as interchange fees and merchant discount fees that are generally recognized when the cardholder’s transaction is approved and settled. Beginning in 2018, credit card rewards accrued to cardholders are recognized as a reduction of interchange revenue. Also included in other revenues from operations are insurance commissions, ATM surcharge fees, and advisory fees. Insurance commissions are recognized at the time the insurance policy is executed with the customer. Insurance renewal commissions are recognized upon subsequent renewal of the policy. ATM surcharge fees are included in revenue at the time of the respective ATM transaction. Advisory fees are generally recognized at the conclusion of the advisory engagement when the Company has satisfied its service obligation.

Recent accounting developments

Recent accounting developments	9 Months Ended
	Sep. 30, 2018
Accounting Changes And Error Corrections [Abstract]
Recent accounting developments	16. Recent accounting developments The following table provides a description of accounting standards that were adopted by the Company in 2018 as well as standards that are not effective that could have an impact to M&T’s consolidated financial statements upon adoption. Standard Description Required date of adoption Effect on consolidated financial statements Standards Adopted in 2018 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. January 1, 2018 As described in note 15 the Company adopted the revenue recognition guidance effective January 1, 2018 and applied the modified retrospective approach for reporting purposes. The adjustment to beginning retained earnings as well as the impact of any changes in the timing of revenue recognition of noninterest income items within the scope of this guidance did not have a material effect on the Company’s financial position or results of operations. Recognition and Measurement of Financial Assets and Financial Liabilities The amended guidance requires 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, public entities to use the exit price when measuring the fair value of financial instruments for disclosure purposes, and 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. January 1, 2018 At January 1, 2018 the Company reclassified marketable equity securities from investment securities available for sale. Upon adoption $17 million of fair value changes in those equity securities, net of tax were reclassified from accumulated other comprehensive income to retained earnings. See note 2 for information on amounts recognized in gain (loss) on bank investment securities in the consolidated statement of income. Improvements to Accounting for Hedging Activities The amended guidance expands and clarifies hedge accounting for nonfinancial and financial risk components, aligns the recognition and presentation of the effects of the hedging instrument and hedged item in the financial statements, and simplifies the requirements for assessing effectiveness in a hedging relationship. January 1, 2019 Early adoption permitted The Company early adopted the amended guidance on January 1, 2018 and such adoption did not have a material impact on its consolidated financial statements. Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost The amended guidance requires 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 component. January 1, 2018 The Company adopted the new reporting requirements effective January 1, 2018. The Company previously reported all of its net periodic pension and postretirement benefit costs in salaries and employee benefits expense within the consolidated statement of income. Information about net periodic pension and postretirement benefit costs that were not service cost-related is included in note 6. The impact of adopting the amended guidance was not material. Scope of Modification Accounting for Share-Based Payment Awards The amended guidance addresses which changes to the terms and conditions of a share-based payment award require an entity to apply modification accounting. January 1, 2018 The Company adopted the amended guidance on January 1, 2018. The guidance is being applied on a prospective basis for awards modified on or after the adoption date. Restricted Cash The amended 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. January 1, 2018 The guidance was adopted on January 1, 2018 and did not have a material impact on the Company’s consolidated financial statements. 16. Recent accounting developments, continued Standard Description Required date of adoption Effect on consolidated financial statements Standards Adopted in 2018 Classification of Certain Cash Receipts and Cash Payments This amendment provides clarifying guidance for classifying cash inflows or outflows on the statement of cash flows where current guidance is unclear or silent. January 1, 2018 The guidance was Clarifying the Definition of a Business The amended guidance clarifies the definition of a business for purposes of evaluating whether transactions would be accounted for as acquisitions (or disposals) of assets or businesses. January 1, 2018 The guidance was adopted January 1, 2018 and will be future transactions Standards Not Yet Adopted as of September 30, 2018 Leases The new guidance requires lessees to record a right-of-use asset and a lease liability for all leases with a term greater than 12 months. 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 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. January 1, 2019 Early adoption permitted 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 expects to recognize increased liabilities in the range of $385 million to $410 million as a result of recognizing lease liabilities on its consolidated balance sheet. However, the determination of the final amount is dependent on the terms of leases in effect and the level of interest rates on January 1, 2019. The Company does not expect the new guidance will have a material impact on its consolidated statement of income. Premium Amortization on Purchased Callable Debt Securities The amended guidance requires the premium on callable debt securities 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. January 1, 2019 Early adoption permitted 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. 16. Recent accounting developments, continued Standard Description Required date of adoption Effect on consolidated financial statements Standards Not Yet Adopted as of September 30, 2018 Measurement of Credit Losses on Financial Instruments The amended guidance replaces the current incurred loss model for determining the allowance for credit losses. The 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. January 1, 2020 Early adoption permitted as of January 1, 2019 The Company is developing its approach for determining expected credit losses under the new guidance. 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 allowances will 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 expected increase to the allowance for credit losses and the impact to the Company’s financial statements are still being determined. Simplifying the Test for Goodwill Impairment The amended guidance eliminates step 2 from the goodwill impairment test. January 1, 2020 Early adoption permitted The amendments should be applied using a prospective transition method. 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. 16. Recent accounting developments, continued Standard Description Required date of adoption Effect on consolidated financial statements Standards Not Yet Adopted as of September 30, 2018 Changes to the Disclosure Requirements for Fair Value Measurements The amended guidance modifies the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurements. The amendments are a result of the disclosure framework project that focuses on improvements to the effectiveness of disclosures in the notes to financial statements. The amendments remove, modify, and add certain disclosure requirements. The disclosure requirements being removed relating to public companies are (1) the amount and reason for transfers between Level 1 and Level 2 of the fair value hierarchy, (2) the policy for timing of transfers between levels, and (3) the valuation process for Level 3 fair value measurements. The disclosure requirements being modified relating to public companies are (1)for investments in certain entities that calculate net asset value, an entity is required to disclose the timing of liquidation of an investee’s asset and the date when restrictions from redemption might lapse only if the investee has communicated the timing to the entity or announced the timing publicly, and (2) the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as a result of the use of unobservable inputs. The disclosure requirements being added relating to public companies are (1) to disclose the changes in unrealized gains and losses for the period for recurring Level 3 fair value measurements, and (2) to disclose the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. January 1, 2020 Early adoption permitted The amendments relating to changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurements uncertainty should be applied prospectively. All other amendments should be applied retrospectively. The Company does not expect the guidance to have a material impact on its consolidated financial statements. Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract The amended guidance requires a hosting arrangement that is a service contract to follow the guidance in Subtopic 350-40 to determine which implementation costs to capitalize and which costs to expense. January 1, 2020 Early adoption permitted The amendments should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company is evaluating the impact that the guidance will have on its consolidated financial statements. 16. Recent accounting developments, continued Standard Description Required date of adoption Effect on consolidated financial statements Standards Not Yet Adopted as of September 30, 2018 Changes to the Disclosure Requirements for Defined Benefit Plans The amended guidance modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. The amendments are a result of the disclosure framework project that focuses on improvements to the effectiveness of disclosures in the notes to financial statements. The amendments remove and add certain disclosure requirements. The disclosure requirements being removed relating to public companies are (1) the amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit cost over the next fiscal year, (2) the amount and timing of plan assets expected to be returned to the employer, (3) the 2001 disclosure requirement relating to Japanese Welfare Pension Insurance Law, (4) related party disclosures about the amount of future annual benefits covered by insurance, and (5) the effects of a one-percentage-point change in assumed health care cost trends on the benefit cost and obligation. The disclosure requirements being added relating to public companies are (1) the weighted-average interest crediting rates for cash balance plans , and (2) an explanation of the reasons for significant gains and losses related to changes in the benefit obligation for the period. January 1, 2021 Early adoption permitted The amendments should be applied retrospectively. The Company does not expect the guidance to have a material impact on its consolidated financial statements.

Significant accounting polici_2

Significant accounting policies (Policies)	9 Months Ended
	Sep. 30, 2018
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, 2017 (“2017 Annual Report”), except that effective January 1, 2018 the Company adopted amended accounting guidance that is discussed in notes 2, 15 and 16 herein. In the opinion of management, all adjustments necessary for a fair presentation have been made and were all of a normal recurring nature.

Investment securities (Tables)

Investment securities (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 1,623,860 8 15,196 $ 1,608,672 Obligations of states and political subdivisions 1,792 9 5 1,796 Mortgage-backed securities: Government issued or guaranteed 7,686,746 9,610 283,660 7,412,696 Privately issued 25 — 2 23 Other debt securities 137,552 1,911 8,135 131,328 9,449,975 11,538 306,998 9,154,515 Investment securities held to maturity: U.S. Treasury and federal agencies 445,199 — 412 444,787 Obligations of states and political subdivisions 8,752 32 18 8,766 Mortgage-backed securities: Government issued or guaranteed 2,842,807 1,912 94,241 2,750,478 Privately issued 117,996 11,025 23,747 105,274 Other debt securities 3,965 — — 3,965 3,418,719 12,969 118,418 3,313,270 Total debt securities $ 12,868,694 24,507 425,416 $ 12,467,785 Equity and other securities: Readily marketable equity — at fair value $ 77,871 13,253 995 $ 90,129 Other — at cost 410,518 — — 410,518 Total equity and other securities $ 488,389 13,253 995 $ 500,647 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In thousands) December 31, 2017 Investment securities available for sale: U.S. Treasury and federal agencies $ 1,965,665 — 18,178 $ 1,947,487 Obligations of states and political subdivisions 2,555 36 2 2,589 Mortgage-backed securities: Government issued or guaranteed 8,755,482 59,497 98,587 8,716,392 Privately issued 28 — — 28 Other debt securities 136,905 2,402 10,475 128,832 Equity securities 78,161 23,219 424 100,956 10,938,796 85,154 127,666 10,896,284 Investment securities held to maturity: Obligations of states and political subdivisions 24,562 109 49 24,622 Mortgage-backed securities: Government issued or guaranteed 3,187,953 27,236 13,746 3,201,443 Privately issued 135,688 2,574 27,575 110,687 Other debt securities 5,010 — — 5,010 3,353,213 29,919 41,370 3,341,762 Other securities — at cost 415,028 — — 415,028 Total $ 14,707,037 115,073 169,036 $ 14,653,074
Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity	At September 30, 2018, 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 $ 1,269,955 1,261,175 Due after one year through five years 361,249 354,788 Due after five years through ten years 101,971 101,055 Due after ten years 30,029 24,778 1,763,204 1,741,796 Mortgage-backed securities available for sale 7,686,771 7,412,719 $ 9,449,975 9,154,515 Debt securities held to maturity: Due in one year or less $ 448,774 448,366 Due after one year through five years 5,177 5,187 Due after ten years 3,965 3,965 457,916 457,518 Mortgage-backed securities held to maturity 2,960,803 2,855,752 $ 3,418,719 3,313,270
Investment Securities in Continuous Unrealized Loss Position	A summary of investment securities that as of September 30, 2018 and December 31, 2017 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, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 9,221 (79 ) 1,601,806 (15,117 ) Obligations of states and political subdivisions 702 (4 ) 375 (1 ) Mortgage-backed securities: Government issued or guaranteed 2,973,861 (80,037 ) 3,628,562 (203,623 ) Privately issued 7 (2 ) — — Other debt securities 15,409 (127 ) 63,639 (8,008 ) 2,999,200 (80,249 ) 5,294,382 (226,749 ) Investment securities held to maturity: U.S. Treasury and federal agencies 444,787 (412 ) — — Obligations of states and political subdivisions 514 (1 ) 3,436 (17 ) Mortgage-backed securities: Government issued or guaranteed 1,762,808 (52,208 ) 800,906 (42,033 ) Privately issued — — 52,180 (23,747 ) 2,208,109 (52,621 ) 856,522 (65,797 ) Total $ 5,207,309 (132,870 ) 6,150,904 (292,546 ) December 31, 2017 Investment securities available for sale: U.S. Treasury and federal agencies $ 278,132 (1,761 ) 1,669,355 (16,417 ) Obligations of states and political subdivisions — — 474 (2 ) Mortgage-backed securities: Government issued or guaranteed 2,106,142 (13,695 ) 3,138,841 (84,892 ) Other debt securities 3,067 (26 ) 61,159 (10,449 ) Equity securities (a) — — 18,162 (424 ) 2,387,341 (15,482 ) 4,887,991 (112,184 ) Investment securities held to maturity: Obligations of states and political subdivisions 2,954 (4 ) 6,110 (45 ) Mortgage-backed securities: Government issued or guaranteed 1,331,759 (7,036 ) 265,695 (6,710 ) Privately issued 5,061 (1,216 ) 55,255 (26,359 ) 1,339,774 (8,256 ) 327,060 (33,114 ) Total $ 3,727,115 (23,738 ) 5,215,051 (145,298 ) (a) Beginning January 1, 2018, equity securities with readily determinable fair values are required to be measured at fair value with changes in fair value recognized in the consolidated statement of income. As a result, subsequent to December 31, 2017 disclosing the time period for which these equity securities had been in a continuous unrealized loss position is no longer relevant.

Loans and leases and the allo_2

Loans and leases and the allowance for credit losses (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Summary of Current, Past Due and Nonaccrual Loans	A summary of current, past due and nonaccrual loans as of September 30, 2018 and December 31, 2017 follows: Current 30-89 Days Past Due Accruing Loans Due 90 Days or More (a) Accruing Loans Acquired a Discount Past Due 90 days or More (b) Purchased Impaired (c) Nonaccrual Total (In thousands) September 30, 2018 Commercial, financial, leasing, etc. $ 21,317,925 81,323 1,390 100 — 234,656 $ 21,635,394 Real estate: Commercial 24,650,660 97,630 52,436 4,277 9,948 207,584 25,022,535 Residential builder and developer 1,631,501 7,354 1,656 114 — 2,786 1,643,411 Other commercial construction 6,792,917 39,598 440 16 571 18,887 6,852,429 Residential 13,989,937 437,170 193,604 7,065 224,618 227,619 15,080,013 Residential — limited documentation 2,373,778 93,582 729 — 90,843 82,454 2,641,386 Consumer: Home equity lines and loans 4,850,989 35,212 — 4,694 — 66,303 4,957,198 Automobile 3,527,867 71,184 — — — 20,949 3,620,000 Other 5,144,471 41,992 4,105 27,957 — 9,594 5,228,119 Total $ 84,280,045 905,045 254,360 44,223 325,980 870,832 $ 86,680,485 December 31, 2017 Commercial, financial, leasing, etc. $ 21,332,234 167,756 1,322 327 21 240,991 $ 21,742,651 Real estate: Commercial 24,910,381 166,305 4,444 6,016 16,815 184,982 25,288,943 Residential builder and developer 1,618,973 5,159 — — 1,135 6,451 1,631,718 Other commercial construction 6,407,451 23,467 — — 4,706 10,088 6,445,712 Residential 15,376,759 474,372 233,437 7,582 282,102 235,834 16,610,086 Residential — limited documentation 2,718,019 83,898 — — 105,236 96,105 3,003,258 Consumer: Home equity lines and loans 5,171,345 38,546 — 9,391 — 74,500 5,293,782 Automobile 3,441,371 78,511 — — — 23,781 3,543,663 Other 4,349,071 40,929 5,202 24,102 — 9,866 4,429,170 Total $ 85,325,604 1,078,943 244,405 47,418 410,015 882,598 $ 87,988,983 (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	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, 2018 2017 (In thousands) Outstanding principal balance $ 1,124,232 1,394,188 Carrying amount: Commercial, financial, leasing, etc. 26,473 31,105 Commercial real estate 165,431 228,054 Residential real estate 507,475 620,827 Consumer 97,125 123,413 $ 796,504 1,003,399
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, 2018 and 2017 follows: Three Months Ended September 30 2018 2017 Purchased Other Purchased Other Impaired Acquired Impaired Acquired (In thousands) Balance at beginning of period $ 149,388 $ 117,715 $ 133,532 $ 163,099 Interest income (8,105 ) (18,001 ) (10,815 ) (20,064 ) Reclassifications from nonaccretable balance 8,445 25 30,799 6,041 Other (a) — 2,001 — 1,545 Balance at end of period $ 149,728 101,740 $ 153,516 $ 150,621 Nine Months Ended September 30 2018 2017 Purchased Other Purchased Other Impaired Acquired Impaired Acquired (In thousands) Balance at beginning of period $ 157,918 $ 133,162 $ 154,233 $ 201,153 Interest income (25,893 ) (48,507 ) (32,546 ) (66,505 ) Reclassifications from nonaccretable balance 17,703 11,230 31,829 11,076 Other (a) — 5,855 — 4,897 Balance at end of period $ 149,728 $ 101,740 $ 153,516 150,621 (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, 2018 were as follows: Commercial, Financial, Real Estate Leasing, etc. Commercial Residential Consumer Unallocated Total (In thousands) Beginning balance $ 328,830 353,761 76,123 182,987 77,547 $ 1,019,248 Provision for credit losses (6,972 ) (11,394 ) 741 32,887 738 16,000 Net charge-offs Charge-offs (11,792 ) (1,941 ) (3,338 ) (34,995 ) — (52,066 ) Recoveries 7,123 14,577 1,655 12,951 — 36,306 Net (charge-offs) recoveries (4,669 ) 12,636 (1,683 ) (22,044 ) — (15,760 ) Ending balance $ 317,189 355,003 75,181 193,830 78,285 $ 1,019,488 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 nine months ended September 30, 2018 were as follows: Commercial, Financial, Real Estate Leasing, etc. Commercial Residential Consumer Unallocated Total (In thousands) Beginning balance $ 328,599 374,085 65,405 170,809 78,300 $ 1,017,198 Provision for credit losses 11,508 (27,464 ) 16,469 93,502 (15 ) 94,000 Net charge-offs Charge-offs (41,273 ) (7,855 ) (11,658 ) (105,479 ) — (166,265 ) Recoveries 18,355 16,237 4,965 34,998 — 74,555 Net (charge-offs) recoveries (22,918 ) 8,382 (6,693 ) (70,481 ) — (91,710 ) Ending balance $ 317,189 355,003 75,181 193,830 78,285 $ 1,019,488 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
Impaired Loans and Leases	I nformation with respect to loans and leases that were considered impaired as of September 30, 2018 and December 31, 2017 and for the three-month and nine-month periods ended September 30, 2018 and 2017 follows. September 30, 2018 December 31, 2017 Recorded Investment Unpaid Principal Balance Related Allowance Recorded Investment Unpaid Principal Balance Related Allowance (In thousands) With an allowance recorded: Commercial, financial, leasing, etc. $ 171,272 193,161 46,554 177,250 194,257 45,488 Real estate: Commercial 123,451 135,167 11,851 67,199 75,084 9,140 Residential builder and developer 6,248 6,782 352 5,320 5,641 308 Other commercial construction 11,287 11,650 878 4,817 20,357 647 Residential 122,627 145,231 5,695 101,724 122,602 4,000 Residential — limited documentation 75,183 91,149 4,000 77,277 92,439 3,900 Consumer: Home equity lines and loans 48,711 53,869 9,269 48,847 53,914 8,812 Automobile 3,445 4,118 705 13,498 15,737 2,811 Other 11,536 17,010 2,365 3,220 5,872 656 573,760 658,137 81,669 499,152 585,903 75,762 With no related allowance recorded: Commercial, financial, leasing, etc. 84,235 115,654 — 89,126 115,327 — Real estate: Commercial 104,753 114,998 — 138,356 149,716 — Residential builder and developer 1,174 1,174 — 5,057 5,296 — Other commercial construction 7,698 11,428 — 5,456 9,130 — Residential 14,651 19,742 — 13,574 18,980 — Residential — limited documentation 5,873 10,190 — 9,588 16,138 — 218,384 273,186 — 261,157 314,587 — Total: Commercial, financial, leasing, etc. 255,507 308,815 46,554 266,376 309,584 45,488 Real estate: Commercial 228,204 250,165 11,851 205,555 224,800 9,140 Residential builder and developer 7,422 7,956 352 10,377 10,937 308 Other commercial construction 18,985 23,078 878 10,273 29,487 647 Residential 137,278 164,973 5,695 115,298 141,582 4,000 Residential — limited documentation 81,056 101,339 4,000 86,865 108,577 3,900 Consumer: Home equity lines and loans 48,711 53,869 9,269 48,847 53,914 8,812 Automobile 3,445 4,118 705 13,498 15,737 2,811 Other 11,536 17,010 2,365 3,220 5,872 656 Total $ 792,144 931,323 81,669 760,309 900,490 75,762
Interest Income Recognized on Impaired Loans	Three Months Ended September 30, 2018 Three Months Ended September 30, 2017 Interest Income Recognized Interest Income Recognized Average Recorded Investment Total Cash Basis Average Recorded Investment Total Cash Basis (In thousands) Commercial, financial, leasing, etc. $ 256,196 1,985 1,985 $ 224,526 391 391 Real estate: Commercial 204,315 1,489 1,489 233,572 1,425 1,425 Residential builder and developer 9,000 — — 8,550 895 895 Other commercial construction 9,623 3,379 3,379 16,578 25 25 Residential 133,337 1,959 773 113,892 1,903 905 Residential — limited documentation 81,729 1,607 481 91,974 1,624 569 Consumer: Home equity lines and loans 48,542 421 62 47,831 419 99 Automobile 7,805 181 20 14,588 251 22 Other 7,450 126 6 3,269 80 2 Total $ 757,997 11,147 8,195 754,780 7,013 4,333 Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 Interest Income Recognized Interest Income Recognized Average Recorded Investment Total Cash Basis Average Recorded Investment Total Cash Basis (In thousands) Commercial, financial, leasing, etc. $ 266,594 4,101 4,101 242,410 1,674 1,674 Real estate: Commercial 184,795 8,447 8,447 205,814 3,213 3,213 Residential builder and developer 9,111 1,682 1,682 14,551 1,791 1,791 Other commercial construction 9,056 3,438 3,438 15,474 958 958 Residential 126,910 6,190 2,612 108,741 5,004 2,285 Residential — limited documentation 83,700 4,763 1,494 94,680 4,573 1,292 Consumer: Home equity lines and loans 48,661 1,268 220 46,829 1,240 290 Automobile 11,189 630 49 15,483 788 62 Other 4,545 299 12 3,430 227 8 Total $ 744,561 30,818 22,055 747,412 19,468 11,573
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, 2018 Pass $ 20,498,610 24,190,472 1,499,791 6,709,973 Criticized accrual 902,128 624,479 140,834 123,569 Criticized nonaccrual 234,656 207,584 2,786 18,887 Total $ 21,635,394 25,022,535 1,643,411 6,852,429 December 31, 2017 Pass $ 20,490,486 24,380,184 1,485,148 6,270,812 Criticized accrual 1,011,174 723,777 140,119 164,812 Criticized nonaccrual 240,991 184,982 6,451 10,088 Total $ 21,742,651 25,288,943 1,631,718 6,445,712
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, 2018 Individually evaluated for impairment $ 46,554 13,081 9,695 12,339 $ 81,669 Collectively evaluated for impairment 270,635 341,922 50,576 181,491 844,624 Purchased impaired — — 14,910 — 14,910 Allocated $ 317,189 355,003 75,181 193,830 $ 941,203 Unallocated 78,285 Total $ 1,019,488 December 31, 2017 Individually evaluated for impairment $ 45,488 10,095 7,900 12,279 $ 75,762 Collectively evaluated for impairment 283,111 363,990 47,645 158,530 853,276 Purchased impaired — — 9,860 — 9,860 Allocated $ 328,599 374,085 65,405 170,809 938,898 Unallocated 78,300 Total $ 1,017,198
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, 2018 Individually evaluated for impairment $ 255,507 254,611 218,334 63,692 $ 792,144 Collectively evaluated for impairment 21,379,887 33,253,245 17,187,604 13,741,625 85,562,361 Purchased impaired — 10,519 315,461 — 325,980 Total $ 21,635,394 33,518,375 17,721,399 13,805,317 $ 86,680,485 December 31, 2017 Individually evaluated for impairment $ 266,376 226,205 202,163 65,565 $ 760,309 Collectively evaluated for impairment 21,476,254 33,117,512 19,023,843 13,201,050 86,818,659 Purchased impaired 21 22,656 387,338 — 410,015 Total $ 21,742,651 33,366,373 19,613,344 13,266,615 $ 87,988,983
Loan Modification Activities that were Considered Troubled Debt Restructurings	The table that follows summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the three-month and nine-month periods ended September 30, 2018 and 2017: Post-modification (a) Number Pre- modification Recorded Investment Principal Deferral Interest Rate Reduction Other Combination of Concession Types Total Three Months Ended September 30, 2018 (Dollars in thousands) Commercial, financial, leasing, etc. 47 $ 6,837 $ 1,683 $ 5 $ — $ 5,018 $ 6,706 Real estate: Commercial 18 11,581 1,493 — 3,475 6,297 11,265 Residential 34 8,182 6,026 — — 3,002 9,028 Residential — limited documentation 3 716 — — — 847 847 Consumer: Home equity lines and loans 17 1,651 220 — — 1,450 1,670 Automobile 30 526 526 — — — 526 Other 2 44 44 — — — 44 Total 151 $ 29,537 $ 9,992 $ 5 $ 3,475 $ 16,614 $ 30,086 Three Months Ended September 30, 2017 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 Post-modification (a) Nine Months Ended September 30, 2018 Number Pre- modification Recorded Investment Principal Deferral Interest Rate Reduction Other Combination of Concession Types Total (Dollars in thousands) Commercial, financial, leasing, etc. 150 $ 96,221 $ 47,029 $ 658 $ 6,111 $ 43,086 $ 96,884 Real estate: Commercial 66 25,561 14,693 175 3,869 7,224 25,961 Other commercial construction 1 752 746 — — — 746 Residential 111 28,769 15,785 — — 15,670 31,455 Residential — limited documentation 8 1,595 467 — — 1,423 1,890 Consumer: Home equity lines and loans 41 3,554 224 — — 3,357 3,581 Automobile 57 1,007 995 — — 12 1,007 Other 4 93 93 — — — 93 Total 438 $ 157,552 $ 80,032 $ 833 $ 9,980 $ 70,772 $ 161,617 Nine Months Ended September 30, 2017 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 (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)

Shareholders' equity (Tables)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Issued and Outstanding Preferred Stock	Issued and outstanding preferred stock of M&T as of September 30, 2018 and December 31, 2017 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 $73.58 per share issued in connection with the Series A preferred stock expire on December 23, 2018 and totaled 180,491 at September 30, 2018. (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. 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.

Pension plans and other postr_2

Pension plans and other postretirement benefits (Tables)	9 Months Ended
	Sep. 30, 2018
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 2018 2017 2018 2017 (In thousands) Service cost $ 5,086 5,048 234 293 Interest cost on projected benefit obligation 18,676 19,818 573 929 Expected return on plan assets (30,781 ) (27,131 ) — — Amortization of prior service cost (credit) 139 139 (1,182 ) (340 ) Amortization of net actuarial loss (gain) 10,948 7,316 (206 ) (247 ) Net periodic benefit cost $ 4,068 5,190 (581 ) 635 Pension Benefits Other Postretirement Benefits Nine Months Ended September 30 2018 2017 2018 2017 (In thousands) Service cost $ 15,258 15,145 703 878 Interest cost on projected benefit obligation 56,029 59,452 1,719 2,787 Expected return on plan assets (92,344 ) (81,393 ) — — Amortization of prior service cost (credit) 417 418 (3,546 ) (1,019 ) Amortization of net actuarial loss (gain) 32,844 21,947 (619 ) (741 ) Net periodic benefit cost $ 12,204 15,569 (1,743 ) 1,905

Earnings per common share (Tabl

Earnings per common share (Tables)	9 Months Ended
	Sep. 30, 2018
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 2018 2017 2018 2017 (In thousands, except per share) Income available to common shareholders: Net income $ 526,091 355,923 1,371,861 1,085,903 Less: Preferred stock dividends (a) (18,130 ) (18,130 ) (54,390 ) (54,604 ) Net income available to common equity 507,961 337,793 1,317,471 1,031,299 Less: Income attributable to unvested stock-based compensation awards (2,598 ) (1,992 ) (6,774 ) (6,288 ) Net income available to common shareholders $ 505,363 335,801 1,310,697 1,025,011 Weighted-average shares outstanding: Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards 143,556 152,245 146,177 153,814 Less: Unvested stock-based compensation awards (734 ) (898 ) (753 ) (948 ) Weighted-average shares outstanding 142,822 151,347 145,424 152,866 Basic earnings per common share $ 3.54 2.22 9.01 6.71 (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 2018 2017 2018 2017 (In thousands, except per share) Net income available to common equity $ 507,961 337,793 1,317,471 1,031,299 Less: Income attributable to unvested stock-based compensation awards (2,596 ) (1,989 ) (6,768 ) (6,276 ) Net income available to common shareholders $ 505,365 335,804 1,310,703 1,025,023 Adjusted weighted-average shares outstanding: Common and unvested stock-based compensation awards 143,556 152,245 146,177 153,814 Less: Unvested stock-based compensation awards (734 ) (898 ) (753 ) (948 ) Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock 154 344 181 427 Adjusted weighted-average shares outstanding 142,976 151,691 145,605 153,293 Diluted earnings per common share $ 3.53 2.21 9.00 6.69

Comprehensive income (Tables)

Comprehensive income (Tables)	9 Months Ended
	Sep. 30, 2018
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 Defined Benefit Total Amount Income Securities (a) Plans Other Before Tax Tax Net (In thousands) Balance — January 1, 2018 $ (59,957 ) (413,168 ) (20,165 ) $ (493,290 ) 129,476 $ (363,814 ) Cumulative effect of change in accounting principle — equity securities (22,795 ) — — (22,795 ) 5,942 (16,853 ) Other comprehensive income before reclassifications: Unrealized holding losses, net (230,135 ) — — (230,135 ) 60,494 (169,641 ) Foreign currency translation adjustment — — (1,783 ) (1,783 ) 374 (1,409 ) Unrealized losses on cash flow hedges — — (26,522 ) (26,522 ) 6,972 (19,550 ) Total other comprehensive income (loss) before reclassifications (230,135 ) — (28,305 ) (258,440 ) 67,840 (190,600 ) Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income: Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities 2,519 — — 2,519 (c) (662 ) 1,857 Gains realized in net income (18 ) — — (18 ) (d) 4 (14 ) Accretion of net gain on terminated cash flow hedges — — (83 ) (83 ) (e) 22 (61 ) Net yield adjustment from cash flow hedges currently in effect — — 7,650 7,650 (e) (2,011 ) 5,639 Amortization of prior service credit — (3,129 ) — (3,129 ) (f) 823 (2,306 ) Amortization of actuarial losses — 32,225 — 32,225 (f) (8,472 ) 23,753 Total other comprehensive income (loss) (227,634 ) 29,096 (20,738 ) (219,276 ) 57,544 (161,732 ) Balance — September 30, 2018 $ (310,386 ) (384,072 ) (40,903 ) $ (735,361 ) 192,962 $ (542,399 ) Investment Securities Defined Benefit Total Amount Income With OTTI (b) 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 HTM securities — 2,535 — — 2,535 (c) (998 ) 1,537 (Gains) losses realized in net income (50 ) 67 — — 17 (d) (7 ) 10 Accretion of net gain on terminated cash flow hedges — — — (109 ) (109 ) (e) 43 (66 ) Net yield adjustment from cash flow hedges currently in effect — — — (2,275 ) (2,275 ) (e) 895 (1,380 ) Amortization of prior service credit — — (601 ) — (601 ) (f) 236 (365 ) Amortization of actuarial losses — — 21,206 — 21,206 (f) (8,345 ) 12,861 Total other comprehensive income (loss) (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 ) (a) Beginning January 1, 2018, equity securities with readily determinable fair values are required to be measured at fair value with changes in fair value recognized in the income statement. Separate presentation of investment securities with an other-than-temporary impairment charge is no longer required. (b) Other-than-temporary impairment (c) Included in interest income (d) Included in gain (loss) on bank investment securities (e) Included in interest expense (f) Included in other costs of operations
Accumulated Other Comprehensive Income (Loss), Net	Accumulated other comprehensive income (loss), net consisted of the following: Investment Defined Benefit Securities Plans Other Total (In thousands) Balance — December 31, 2017 $ (44,150 ) (304,546 ) (15,118 ) $ (363,814 ) Cumulative effect of change in accounting principle — equity securities (16,853 ) — — (16,853 ) Net gain (loss) during period (167,798 ) 21,447 (15,381 ) (161,732 ) Balance — September 30, 2018 $ (228,801 ) (283,099 ) (30,499 ) $ (542,399 )

Derivative financial instrume_2

Derivative financial instruments (Tables)	9 Months Ended
	Sep. 30, 2018
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: Notional Average Weighted- Average Rate Estimated Fair Amount Maturity Fixed Variable Value (In thousands) (In years) (In thousands) September 30, 2018 Fair value hedges: Fixed rate long-term borrowings (b) $ 5,200,000 2.7 2.45 % 2.76 % $ 1,458 Cash flow hedges: Interest payments on variable rate commercial real estate loans (b)(c) 10,550,000 1.4 1.52 % 2.11 % 988 Total $ 15,750,000 1.8 $ 2,446 December 31, 2017 Fair value hedges: Fixed rate long-term borrowings (b) $ 4,550,000 2.9 2.27 % 2.09 % $ 573 Cash flow hedges: Interest payments on variable rate commercial real estate loans (b)(d) 4,850,000 2.0 1.52 % 1.36 % 66 Total $ 9,400,000 2.5 $ 639 (a) Certain clearinghouse exchanges consider payments by counterparties for variation margin on derivative instruments to be settlements of those positions. The impact of such treatment at September 30, 2018 and December 31, 2017 was a reduction of the estimated fair value losses on interest rate swap agreements designated as fair value hedges of $110.3 million and $41.1 million, respectively, and on interest rate swap agreements designated as cash flow hedges of $36.1 million and $16.3 million, respectively. (b) Under the terms of these agreements, the Company receives settlement amounts at a fixed rate and pays at a variable rate. (c) (d)
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, December 31, September 30, December 31, 2018 2017 2018 2017 (In thousands) Derivatives designated and qualifying as hedging instruments Interest rate swap agreements (a) $ 2,446 $ 639 $ — $ — Commitments to sell real estate loans (a) 5,832 734 546 283 8,278 1,373 546 283 Derivatives not designated and qualifying as hedging instruments Mortgage-related commitments to originate real estate loans for sale (a) 5,625 8,797 1,439 494 Commitments to sell real estate loans (a) 5,795 2,526 250 1,019 Trading: Interest rate contracts (b) 62,472 74,164 299,791 132,104 Foreign exchange and other option and futures contracts (b) 9,270 5,657 8,942 5,286 83,162 91,144 310,422 138,903 Total derivatives $ 91,440 $ 92,517 $ 310,968 $ 139,186 (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 variation margin payments at September 30, 2018 and December 31, 2017 Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount of the Hedged Item September 30, December 31, September 30, December 31, 2018 2017 2018 2017 (In thousands) Location in the Consolidated Balance Sheet of the Hedged Items in Fair Value Hedges Long-term debt $ 5,085,610 $ 4,504,029 $ (108,994 ) $ (40,133 )
Information about Fair Values of Derivative Instruments in Consolidated Statement of Income	Amount of Gain (Loss) Recognized Three Months Ended September 30, 2018 Three Months Ended September 30, 2017 Derivative Hedged Item Derivative Hedged Item (In thousands) Derivatives in fair value hedging relationships Interest rate swap agreements: Fixed rate long-term borrowings (a) $ (12,568 ) 12,607 $ (13,509 ) 14,026 Derivatives not designated as hedging instruments Trading: Interest rate contracts (b) $ (1,348 ) $ (418 ) Foreign exchange and other option and futures contracts (b) 782 1,362 Total $ (566 ) $ 944 9. Derivative financial instruments, continued Amount of Gain (Loss) Recognized Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 Derivative Hedged Item Derivative Hedged Item (In thousands) Derivatives in fair value hedging relationships Interest rate swap agreements: Fixed rate long-term borrowings (a) $ (68,315 ) 68,861 $ (23,423 ) 23,049 Derivatives not designated as hedging instruments Trading: Interest rate contracts (b) $ (5,639 ) $ 2,363 Foreign exchange and other option and futures contracts (b) 5,778 4,766 Total $ 139 $ 7,129 (a) Effective January 1, 2018, reported as an adjustment to interest expense. Prior to 2018, reported as other revenues from operations. (b) Reported as trading account and foreign exchange gains.

Fair value measurements (Tables

Fair value measurements (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 and December 31, 2017 measured at estimated fair value on a recurring basis: Fair Value Measurements Level 1 (a) Level 2 (a) Level 3 (In thousands) September 30, 2018 Trading account assets $ 125,038 $ 47,653 $ 77,385 $ — Investment securities available for sale: U.S. Treasury and federal agencies 1,608,672 — 1,608,672 — Obligations of states and political subdivisions 1,796 — 1,796 — Mortgage-backed securities: Government issued or guaranteed 7,412,696 — 7,412,696 — Privately issued 23 — — 23 Other debt securities 131,328 — 131,328 — 9,154,515 — 9,154,492 23 Equity securities 90,129 72,651 17,478 — Real estate loans held for sale 638,579 — 638,579 — Other assets (b) 19,698 — 14,073 5,625 Total assets $ 10,027,959 $ 120,304 $ 9,902,007 $ 5,648 Trading account liabilities $ 308,733 $ — $ 308,733 $ — Other liabilities (b) 2,235 — 796 1,439 Total liabilities $ 310,968 $ — $ 309,529 $ 1,439 December 31, 2017 Trading account assets $ 132,909 $ 47,873 $ 85,036 $ — Investment securities available for sale: U.S. Treasury and federal agencies 1,947,487 — 1,947,487 — Obligations of states and political subdivisions 2,589 — 2,589 — Mortgage-backed securities: Government issued or guaranteed 8,716,392 — 8,716,392 — Privately issued 28 — — 28 Other debt securities 128,832 — 128,832 — Equity securities 100,956 73,232 27,724 — 10,896,284 73,232 10,823,024 28 Real estate loans held for sale 378,047 — 378,047 — Other assets (b) 12,696 — 3,899 8,797 Total assets $ 11,419,936 $ 121,105 $ 11,290,006 $ 8,825 Trading account liabilities $ 137,390 $ — $ 137,390 $ — Other liabilities (b) 1,796 — 1,302 494 Total liabilities $ 139,186 $ — $ 138,692 $ 494 (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, 2017. (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, 2018 were as follows: Investment Securities Available for S Privately Issued Mortgage-Backed Securities Other Assets and Other Liabilities (In thousands) Balance — June 30, 2018 $ 24 10,751 Total gains (losses) realized/unrealized: Included in earnings — 10,284 (b) Settlements (1 ) — Transfers out of Level 3 (a) — (16,849 ) (c) Balance — September 30, 2018 $ 23 4,186 Changes in unrealized gains included in earnings related to assets still held at September 30, 2018 $ — 4,508 (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, 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 out of Level 3 (a) — (21,016 ) (c) 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) 11. 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, 2018 were as follows: Investment securities available for sale Privately Issued Mortgage-Backed Securities Other Assets and Other Liabilities (In thousands) Balance — January 1, 2018 $ 28 8,303 Total gains (losses) realized/unrealized: Included in earnings — 38,691 (b) Settlements (5 ) — Transfers out of Level 3 (a) — (42,808 ) (c) Balance — September 30, 2018 $ 23 4,186 Changes in unrealized gains included in earnings related to assets still held at September 30, 2018 $ — 3,663 (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, 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 out of Level 3 (a) — (59,427 ) (c) 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) (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) Transfers out of Level 3 consist of interest rate locks transferred to closed loans.
Quantitative Information Related to Significant Unobservable Inputs	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, 2018 and December 31, 2017: Fair Value Valuation Technique Unobservable Inputs/Assumptions Range (Weighted- Average) (In thousands) September 30, 2018 Recurring fair value measurements Privately issued mortgage-backed securities $ 23 Two independent pricing quotes — — Net other assets (liabilities) (a) 4,186 Discounted cash flow Commitment expirations 0%-90% (16%) December 31, 2017 Recurring fair value measurements Privately issued mortgage-backed securities $ 28 Two independent pricing quotes — — Net other assets (liabilities) (a) 8,303 Discounted cash flow Commitment expirations 0%-78% (22%) (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, 2018 Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 (In thousands) Financial assets: Cash and cash equivalents $ 1,311,611 1,311,611 1,232,393 79,218 — Interest-bearing deposits at banks 6,523,746 6,523,746 — 6,523,746 — Trading account assets 125,038 125,038 47,653 77,385 — Investment securities 13,073,881 12,968,432 72,651 12,790,484 105,297 Loans and leases: Commercial loans and leases 21,635,394 21,215,945 — — 21,215,945 Commercial real estate loans 33,518,375 32,971,832 — 381,007 32,590,825 Residential real estate loans 17,721,399 17,429,777 — 3,984,387 13,445,390 Consumer loans 13,805,317 13,676,356 — — 13,676,356 Allowance for credit losses (1,019,488 ) — — — — Loans and leases, net 85,660,997 85,293,910 — 4,365,394 80,928,516 Accrued interest receivable 349,903 349,903 — 349,903 — Financial liabilities: Noninterest-bearing deposits $ (31,773,560 ) (31,773,560 ) — (31,773,560 ) — Savings and interest-checking deposits (51,108,962 ) (51,108,962 ) — (51,108,962 ) — Time deposits (5,810,587 ) (5,872,516 ) — (5,872,516 ) — Deposits at Cayman Islands office (447,287 ) (447,287 ) — (447,287 ) — Short-term borrowings (1,310,110 ) (1,310,110 ) — (1,310,110 ) — Long-term borrowings (9,140,268 ) (9,160,009 ) — (9,160,009 ) — Accrued interest payable (68,196 ) (68,196 ) — (68,196 ) — Trading account liabilities (308,733 ) (308,733 ) — (308,733 ) — Other financial instruments: Commitments to originate real estate loans for sale $ 4,186 4,186 — — 4,186 Commitments to sell real estate loans 10,831 10,831 — 10,831 — Other credit-related commitments (129,102 ) (129,102 ) — — (129,102 ) Interest rate swap agreements used for interest rate risk management 2,446 2,446 — 2,446 — December 31, 2017 Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 (In thousands) Financial assets: Cash and cash equivalents $ 1,420,888 1,420,888 1,352,035 68,853 — Interest-bearing deposits at banks 5,078,903 5,078,903 — 5,078,903 — Trading account assets 132,909 132,909 47,873 85,036 — Investment securities 14,664,525 14,653,074 73,232 14,469,127 110,715 Loans and leases: Commercial loans and leases 21,742,651 21,321,282 — — 21,321,282 Commercial real estate loans 33,366,373 32,950,724 — 22,130 32,928,594 Residential real estate loans 19,613,344 19,596,826 — 4,440,645 15,156,181 Consumer loans 13,266,615 13,161,517 — — 13,161,517 Allowance for credit losses (1,017,198 ) — — — — Loans and leases, net 86,971,785 87,030,349 — 4,462,775 82,567,574 Accrued interest receivable 327,170 327,170 — 327,170 — Financial liabilities: Noninterest-bearing deposits $ (33,975,180 ) (33,975,180 ) — (33,975,180 ) — Savings and interest-checking deposits (51,698,008 ) (51,698,008 ) — (51,698,008 ) — Time deposits (6,580,962 ) (6,635,048 ) — (6,635,048 ) — Deposits at Cayman Islands office (177,996 ) (177,996 ) — (177,996 ) — Short-term borrowings (175,099 ) (175,099 ) — (175,099 ) — Long-term borrowings (8,141,430 ) (8,193,783 ) — (8,193,783 ) — Accrued interest payable (75,641 ) (75,641 ) — (75,641 ) — Trading account liabilities (137,390 ) (137,390 ) — (137,390 ) — Other financial instruments: Commitments to originate real estate loans for sale $ 8,303 8,303 — — 8,303 Commitments to sell real estate loans 1,958 1,958 — 1,958 — Other credit-related commitments (125,281 ) (125,281 ) — — (125,281 ) Interest rate swap agreements used for interest rate risk management 639 639 — 639 —

Commitments and contingencies (

Commitments and contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 2017 (In thousands) Commitments to extend credit Home equity lines of credit $ 5,465,893 5,482,622 Commercial real estate loans to be sold 153,900 194,763 Other commercial real estate 6,549,168 6,050,569 Residential real estate loans to be sold 307,955 347,113 Other residential real estate 267,948 201,426 Commercial and other 14,608,286 12,733,815 Standby letters of credit 2,385,904 2,497,844 Commercial letters of credit 42,030 46,739 Financial guarantees and indemnification contracts 3,416,625 3,434,381 Commitments to sell real estate loans 994,879 812,217

Segment information (Tables)

Segment information (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Information about Company's Segments	Information about the Company's segments is presented in the following table: Three Months Ended September 30 2018 2017 Total Revenues(a) Inter- segment Revenues Net Income (Loss) Total Revenues(a) Inter- segment Revenues Net Income (Loss) (In thousands) Business Banking $ 138,898 920 43,730 $ 130,501 919 31,408 Commercial Banking 280,671 875 147,910 267,822 840 109,797 Commercial Real Estate 214,266 371 116,386 212,014 401 97,295 Discretionary Portfolio 53,061 (10,270 ) 39,723 65,808 (12,346 ) 31,515 Residential 79,603 15,402 13,289 90,018 18,866 13,546 Retail Banking 427,452 2,862 141,612 392,542 2,668 96,329 All Other 294,381 (10,160 ) 23,441 257,858 (11,348 ) (23,967 ) Total $ 1,488,332 — 526,091 $ 1,416,563 — 355,923 Nine Months Ended September 30 2018 2017 Total Revenues(a) Inter- segment Revenues Net Income (Loss) Total Revenues(a) Inter- segment Revenues Net Income (Loss) (In thousands) Business Banking $ 402,811 2,750 124,455 $ 375,816 2,836 85,146 Commercial Banking 816,566 2,653 399,766 818,846 2,603 328,211 Commercial Real Estate 622,414 1,096 337,380 604,437 1,165 269,113 Discretionary Portfolio 162,075 (31,656 ) 88,575 216,798 (37,670 ) 95,200 Residential Mortgage Banking 244,228 46,870 43,637 264,120 55,221 37,206 Retail Banking 1,241,468 8,434 408,081 1,144,964 8,760 282,614 All Other 899,184 (30,147 ) (30,033 ) 751,703 (32,915 ) (11,587 ) Total $ 4,388,746 — 1,371,861 $ 4,176,684 — 1,085,903 13. Segment information, continued Average Total Assets Nine Months Ended September 30 Year Ended December 31 2018 2017 2017 (In millions) Business Banking $ 5,637 5,596 5,602 Commercial Banking 26,524 26,699 26,573 Commercial Real Estate 22,899 22,800 22,741 Discretionary Portfolio 32,659 37,807 37,203 Residential Mortgage Banking 2,123 2,335 2,355 Retail Banking 13,522 12,519 12,702 All Other 13,312 13,317 13,684 Total $ 116,676 121,073 120,860 (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 $5,733,000 and $8,828,000 for the three-month periods ended September 30, 2018 and 2017, respectively, and $15,939,000 and $25,563,000 for the nine-month periods ended September 30, 2018 and 2017, 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.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	9 Months Ended
	Sep. 30, 2018
ASU 2014-09 [Member]
Summary of Sources of M&T's Noninterest Income that are Subject to the Amended Guidance	The following tables summarize sources of M&T’s noninterest income during 2018 that are subject to the amended guidance. Three Months Ended September 30, 2018 Business Banking Commercial Banking Commercial Real Estate Discretionary Portfolio Residential Mortgage Banking Retail Banking All Other Total (In thousands) Classification in consolidated statement of income Service charges on deposit accounts $ 15,767 24,167 2,374 — 2 64,709 1,628 $ 108,647 Trust income — — — — — — 133,545 133,545 Brokerage services income — — — — — — 12,267 12,267 Other revenues from operations: Merchant discount and credit card fees 9,238 13,520 643 — — 3,908 462 27,771 Other — 1,662 1,822 386 916 9,397 6,723 20,906 $ 25,005 39,349 4,839 386 918 78,014 154,625 $ 303,136 15. Revenue from contracts with customers, continued Nine Months Ended September 30, 2018 Business Banking Commercial Banking Commercial Real Estate Discretionary Portfolio Residential Mortgage Banking Retail Banking All Other Total (In thousands) Classification in consolidated statement of income Service charges on deposit accounts $ 46,782 73,091 7,589 — 8 188,325 4,751 $ 320,546 Trust income — — — — — — 402,561 402,561 Brokerage services income — — — — — — 38,288 38,288 Other revenues from operations: Merchant discount and credit card fees 25,075 38,774 1,625 — — 11,436 1,695 78,605 Other — 6,871 4,896 1,251 2,886 28,875 23,429 68,208 $ 71,857 118,736 14,110 1,251 2,894 228,636 470,724 $ 908,208

Investment Securities - Additio

Investment Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)Security	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Security	Sep. 30, 2017USD ($)
Investment Holdings [Line Items]
Loss on bank investment securities	$ (3,415,000)		$ (10,520,000)	$ (17,000)
Gross realized gains(loss) on sale of investment securities	$ 0	$ 0	$ 0	$ 0
Number of debt securities with aggregate gross unrealized losses | Security	1,503		1,503
Unrealized losses on individual debt securities			$ (425,000,000)
Cost method equity securities	$ 411,000,000		411,000,000
Retained Earnings [Member] | Adjustments for New Accounting Pronouncement [Member]
Investment Holdings [Line Items]
Reclassification from accumulated comprehensive income to retained earnings, net of tax	$ 17,000,000		$ 17,000,000

Investment Securities - Amortiz

Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	$ 9,449,975	$ 10,938,796
Investment securities available for sale, gross unrealized gains	11,538	85,154
Investment securities available for sale, gross unrealized losses	306,998	127,666
Investment securities available for sale, estimated fair value	9,154,515	10,896,284
Amortized cost for held to maturity	3,418,719	3,353,213
Gross unrealized gains for held to maturity	12,969	29,919
Gross unrealized losses for held to maturity	118,418	41,370
Estimated fair value for held to maturity	3,313,270	3,341,762
Equity and other securities, Amortized Cost	488,389	415,028
Equity securities, Gross Unrealized Gains	13,253
Equity securities, Gross Unrealized Losses	995
Equity and other securities, Estimated Fair Value	500,647	415,028
Other securities, Amortized cost	410,518	415,028
Other securities, Estimated fair value	410,518	415,028
Total debt securities Amortized cost	12,868,694
Total debt securities Gross unrealized gains	24,507
Total debt securities Gross unrealized losses	425,416
Total debt securities Estimated fair value	12,467,785
Readily marketable securities Amortized cost	77,871
Readily marketable securities Gross unrealized gains	13,253
Readily marketable securities Gross unrealized losses	995
Readily marketable securities Estimated fair value	90,129
Total Amortized cost		14,707,037
Total for Gross unrealized gains		115,073
Total for Gross unrealized losses		169,036
Total for Estimated fair value		14,653,074
U.S. Treasury and Federal Agencies [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	1,623,860	1,965,665
Investment securities available for sale, gross unrealized gains	8
Investment securities available for sale, gross unrealized losses	15,196	18,178
Investment securities available for sale, estimated fair value	1,608,672	1,947,487
Amortized cost for held to maturity	445,199
Gross unrealized losses for held to maturity	412
Estimated fair value for held to maturity	444,787
Obligations of States and Political Subdivisions [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	1,792	2,555
Investment securities available for sale, gross unrealized gains	9	36
Investment securities available for sale, gross unrealized losses	5	2
Investment securities available for sale, estimated fair value	1,796	2,589
Amortized cost for held to maturity	8,752	24,562
Gross unrealized gains for held to maturity	32	109
Gross unrealized losses for held to maturity	18	49
Estimated fair value for held to maturity	8,766	24,622
Government Issued or Guaranteed [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	7,686,746	8,755,482
Investment securities available for sale, gross unrealized gains	9,610	59,497
Investment securities available for sale, gross unrealized losses	283,660	98,587
Investment securities available for sale, estimated fair value	7,412,696	8,716,392
Amortized cost for held to maturity	2,842,807	3,187,953
Gross unrealized gains for held to maturity	1,912	27,236
Gross unrealized losses for held to maturity	94,241	13,746
Estimated fair value for held to maturity	2,750,478	3,201,443
Privately Issued [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	25	28
Investment securities available for sale, gross unrealized losses	2
Investment securities available for sale, estimated fair value	23	28
Amortized cost for held to maturity	117,996	135,688
Gross unrealized gains for held to maturity	11,025	2,574
Gross unrealized losses for held to maturity	23,747	27,575
Estimated fair value for held to maturity	105,274	110,687
Other Debt Securities [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	137,552	136,905
Investment securities available for sale, gross unrealized gains	1,911	2,402
Investment securities available for sale, gross unrealized losses	8,135	10,475
Investment securities available for sale, estimated fair value	131,328	128,832
Amortized cost for held to maturity	3,965	5,010
Estimated fair value for held to maturity	$ 3,965	5,010
Equity Securities [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost		78,161
Investment securities available for sale, gross unrealized gains		23,219
Investment securities available for sale, gross unrealized losses		424
Investment securities available for sale, estimated fair value		$ 100,956

Investment Securities - Amort_2

Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt securities available for sale:
Due in one year or less	$ 1,269,955
Due after one year through five years	361,249
Due after five years through ten years	101,971
Due after ten years	30,029
Total available for sale (amortized cost)	1,763,204
Mortgage-backed securities available for sale	7,686,771
Investment securities available for sale, amortized cost	9,449,975	$ 10,938,796
Debt securities held to maturity:
Due in one year or less	448,774
Due after one year through five years	5,177
Due after ten years	3,965
Total available for held to maturity (amortized cost)	457,916
Mortgage-backed securities held to maturity	2,960,803
Amortized cost for held to maturity	3,418,719	3,353,213
Debt securities available for sale:
Due in one year or less	1,261,175
Due after one year through five years	354,788
Due after five years through ten years	101,055
Due after ten years	24,778
Total available for sale (fair value)	1,741,796
Mortgage-backed securities available for sale	7,412,719
Total	9,154,515	10,896,284
Debt securities held to maturity:
Due in one year or less	448,366
Due after one year through five years	5,187
Due after ten years	3,965
Total available for held to maturity (fair value)	457,518
Mortgage-backed securities held to maturity	2,855,752
Total	$ 3,313,270	$ 3,341,762

Investment Securities - Investm

Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	$ 2,999,200	$ 2,387,341
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(80,249)	(15,482)
Estimated fair value, 12 months or more	5,294,382	4,887,991
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(226,749)	(112,184)
Held to maturity, Estimated fair value, Less than 12 months	2,208,109	1,339,774
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(52,621)	(8,256)
Held to maturity, Estimated fair value, 12 months or more	856,522	327,060
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(65,797)	(33,114)
Total investment securities, fair value less than 12 months	5,207,309	3,727,115
Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses	(132,870)	(23,738)
Total of investment securities, fair value, 12 Months or More	6,150,904	5,215,051
Investment Securities Continuous Unrealized Loss Position Twelve Months or Longer Aggregate Losses	(292,546)	(145,298)
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	9,221	278,132
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(79)	(1,761)
Estimated fair value, 12 months or more	1,601,806	1,669,355
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(15,117)	(16,417)
Held to maturity, Estimated fair value, Less than 12 months	444,787
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(412)
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	702
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(4)
Estimated fair value, 12 months or more	375	474
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(1)	(2)
Held to maturity, Estimated fair value, Less than 12 months	514	2,954
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(1)	(4)
Held to maturity, Estimated fair value, 12 months or more	3,436	6,110
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(17)	(45)
Government Issued or Guaranteed [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	2,973,861	2,106,142
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(80,037)	(13,695)
Estimated fair value, 12 months or more	3,628,562	3,138,841
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(203,623)	(84,892)
Held to maturity, Estimated fair value, Less than 12 months	1,762,808	1,331,759
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(52,208)	(7,036)
Held to maturity, Estimated fair value, 12 months or more	800,906	265,695
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(42,033)	(6,710)
Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	7
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(2)
Held to maturity, Estimated fair value, Less than 12 months		5,061
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses		(1,216)
Held to maturity, Estimated fair value, 12 months or more	52,180	55,255
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(23,747)	(26,359)
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	15,409	3,067
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(127)	(26)
Estimated fair value, 12 months or more	63,639	61,159
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	$ (8,008)	(10,449)
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, 12 months or more		18,162
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses		$ (424)

Loans and Leases and the Allo_3

Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 84,280,045	$ 85,325,604
30-89 Days Past Due	905,045	1,078,943
Accruing Loans Past Due 90 Days or More	254,360	244,405
Purchased Impaired	325,980	410,015
Nonaccrual	870,832	882,598
Loans and leases, net of unearned discount	86,680,485	87,988,983
Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	44,223	47,418
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,317,925	21,332,234
30-89 Days Past Due	81,323	167,756
Accruing Loans Past Due 90 Days or More	1,390	1,322
Purchased Impaired		21
Nonaccrual	234,656	240,991
Loans and leases, net of unearned discount	21,635,394	21,742,651
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	100	327
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	24,650,660	24,910,381
30-89 Days Past Due	97,630	166,305
Accruing Loans Past Due 90 Days or More	52,436	4,444
Purchased Impaired	9,948	16,815
Nonaccrual	207,584	184,982
Loans and leases, net of unearned discount	25,022,535	25,288,943
Commercial [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	4,277	6,016
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,631,501	1,618,973
30-89 Days Past Due	7,354	5,159
Accruing Loans Past Due 90 Days or More	1,656
Purchased Impaired		1,135
Nonaccrual	2,786	6,451
Loans and leases, net of unearned discount	1,643,411	1,631,718
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	114
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	6,792,917	6,407,451
30-89 Days Past Due	39,598	23,467
Accruing Loans Past Due 90 Days or More	440
Purchased Impaired	571	4,706
Nonaccrual	18,887	10,088
Loans and leases, net of unearned discount	6,852,429	6,445,712
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	16
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	13,989,937	15,376,759
30-89 Days Past Due	437,170	474,372
Accruing Loans Past Due 90 Days or More	193,604	233,437
Purchased Impaired	224,618	282,102
Nonaccrual	227,619	235,834
Loans and leases, net of unearned discount	15,080,013	16,610,086
Residential [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	7,065	7,582
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,373,778	2,718,019
30-89 Days Past Due	93,582	83,898
Accruing Loans Past Due 90 Days or More	729
Purchased Impaired	90,843	105,236
Nonaccrual	82,454	96,105
Loans and leases, net of unearned discount	2,641,386	3,003,258
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,850,989	5,171,345
30-89 Days Past Due	35,212	38,546
Nonaccrual	66,303	74,500
Loans and leases, net of unearned discount	4,957,198	5,293,782
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	4,694	9,391
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,527,867	3,441,371
30-89 Days Past Due	71,184	78,511
Nonaccrual	20,949	23,781
Loans and leases, net of unearned discount	3,620,000	3,543,663
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,144,471	4,349,071
30-89 Days Past Due	41,992	40,929
Accruing Loans Past Due 90 Days or More	4,105	5,202
Nonaccrual	9,594	9,866
Loans and leases, net of unearned discount	5,228,119	4,429,170
Other [Member] | Accruing Loans Acquired at Discount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing Loans Past Due 90 Days or More	$ 27,957	$ 24,102

Loans and Leases and the Allo_4

Loans and Leases and the Allowance for Credit Losses - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Loans And Leases Receivable [Line Items]
Commercial real estate loans held for sale	$ 381	$ 22
Contractual principal and interest payments	$ 326	410
Minimum delinquency period for loan level collectability analysis consumer mortgage	150 days
Amount of foreclosed residential real estate property held	$ 85	108
Loans secured by residential real estate that were in the process of foreclosure	$ 404	497
Percentage loans in the process of foreclosure, serviced by other entities, classified as purchased impaired	40.00%
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	$ 258	356
Carrying value of loans for which partial charge-off has been recognized	29	34
Mortgage loans on real real estate not requiring charge off due to collateral carrying amount	18	20
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	23	25
Mortgage loans on real real estate not requiring charge off due to collateral carrying amount	$ 29	$ 32
Maximum [Member]
Loans And Leases Receivable [Line Items]
Purchased impaired loans as a percentage of total assets	1.00%	1.00%
Minimum [Member]
Loans And Leases Receivable [Line Items]
Loan delinquent period	90 days

Loans and Leases and the Allo_5

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, 2018	Dec. 31, 2017
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$ 1,124,232	$ 1,394,188
Carrying amount	796,504	1,003,399
Commercial, Financial, Leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	26,473	31,105
Commercial Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	165,431	228,054
Residential Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	507,475	620,827
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$ 97,125	$ 123,413

Loans and Leases and the Allo_6

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 149,388	$ 133,532	$ 157,918	$ 154,233
Interest income	(8,105)	(10,815)	(25,893)	(32,546)
Reclassifications from nonaccretable balance	8,445	30,799	17,703	31,829
Balance at end of period	149,728	153,516	149,728	153,516
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	117,715	163,099	133,162	201,153
Interest income	(18,001)	(20,064)	(48,507)	(66,505)
Reclassifications from nonaccretable balance	25	6,041	11,230	11,076
Other	2,001	1,545	5,855	4,897
Balance at end of period	$ 101,740	$ 150,621	$ 101,740	$ 150,621

Loans and Leases and the Allo_7

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,019,248	$ 1,008,225	$ 1,017,198	$ 988,997
Provision for credit losses	16,000	30,000	94,000	137,000
Net charge-offs
Charge-offs	(52,066)	(47,052)	(166,265)	(171,298)
Recoveries	36,306	22,153	74,555	58,627
Net (charge-offs) recoveries	(15,760)	(24,899)	(91,710)	(112,671)
Ending balance	1,019,488	1,013,326	1,019,488	1,013,326
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	328,830	339,314	328,599	330,833
Provision for credit losses	(6,972)	2,451	11,508	44,642
Net charge-offs
Charge-offs	(11,792)	(9,714)	(41,273)	(51,318)
Recoveries	7,123	4,423	18,355	12,317
Net (charge-offs) recoveries	(4,669)	(5,291)	(22,918)	(39,001)
Ending balance	317,189	336,474	317,189	336,474
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	353,761	366,229	374,085	362,719
Provision for credit losses	(11,394)	(7,699)	(27,464)	1,201
Net charge-offs
Charge-offs	(1,941)	(258)	(7,855)	(7,556)
Recoveries	14,577	5,895	16,237	7,803
Net (charge-offs) recoveries	12,636	5,637	8,382	247
Ending balance	355,003	364,167	355,003	364,167
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	76,123	66,006	65,405	61,127
Provision for credit losses	741	1,267	16,469	14,067
Net charge-offs
Charge-offs	(3,338)	(4,206)	(11,658)	(16,364)
Recoveries	1,655	2,028	4,965	6,265
Net (charge-offs) recoveries	(1,683)	(2,178)	(6,693)	(10,099)
Ending balance	75,181	65,095	75,181	65,095
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	182,987	158,559	170,809	156,288
Provision for credit losses	32,887	33,886	93,502	76,908
Net charge-offs
Charge-offs	(34,995)	(32,874)	(105,479)	(96,060)
Recoveries	12,951	9,807	34,998	32,242
Net (charge-offs) recoveries	(22,044)	(23,067)	(70,481)	(63,818)
Ending balance	193,830	169,378	193,830	169,378
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	77,547	78,117	78,300	78,030
Provision for credit losses	738	95	(15)	182
Net charge-offs
Ending balance	$ 78,285	$ 78,212	$ 78,285	$ 78,212

Loans and Leases and the Allo_8

Loans and Leases and the Allowance for Credit Losses - Impaired Loans and Leases (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	$ 573,760	$ 499,152
Unpaid principal balance with related allowance	658,137	585,903
Related allowance	81,669	75,762
Recorded investment with no related allowance	218,384	261,157
Unpaid principal balance with no related allowance	273,186	314,587
Recorded investment	792,144	760,309
Unpaid principal balance	931,323	900,490
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	123,451	67,199
Unpaid principal balance with related allowance	135,167	75,084
Related allowance	11,851	9,140
Recorded investment with no related allowance	104,753	138,356
Unpaid principal balance with no related allowance	114,998	149,716
Recorded investment	228,204	205,555
Unpaid principal balance	250,165	224,800
Automobile [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	3,445	13,498
Unpaid principal balance with related allowance	4,118	15,737
Related allowance	705	2,811
Recorded investment	3,445	13,498
Unpaid principal balance	4,118	15,737
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	171,272	177,250
Unpaid principal balance with related allowance	193,161	194,257
Related allowance	46,554	45,488
Recorded investment with no related allowance	84,235	89,126
Unpaid principal balance with no related allowance	115,654	115,327
Recorded investment	255,507	266,376
Unpaid principal balance	308,815	309,584
Residential Builder and Developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	6,248	5,320
Unpaid principal balance with related allowance	6,782	5,641
Related allowance	352	308
Recorded investment with no related allowance	1,174	5,057
Unpaid principal balance with no related allowance	1,174	5,296
Recorded investment	7,422	10,377
Unpaid principal balance	7,956	10,937
Other Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	11,287	4,817
Unpaid principal balance with related allowance	11,650	20,357
Related allowance	878	647
Recorded investment with no related allowance	7,698	5,456
Unpaid principal balance with no related allowance	11,428	9,130
Recorded investment	18,985	10,273
Unpaid principal balance	23,078	29,487
Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	122,627	101,724
Unpaid principal balance with related allowance	145,231	122,602
Related allowance	5,695	4,000
Recorded investment with no related allowance	14,651	13,574
Unpaid principal balance with no related allowance	19,742	18,980
Recorded investment	137,278	115,298
Unpaid principal balance	164,973	141,582
Residential Limited Documentation [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	75,183	77,277
Unpaid principal balance with related allowance	91,149	92,439
Related allowance	4,000	3,900
Recorded investment with no related allowance	5,873	9,588
Unpaid principal balance with no related allowance	10,190	16,138
Recorded investment	81,056	86,865
Unpaid principal balance	101,339	108,577
Home Equity Lines and Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	48,711	48,847
Unpaid principal balance with related allowance	53,869	53,914
Related allowance	9,269	8,812
Recorded investment	48,711	48,847
Unpaid principal balance	53,869	53,914
Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	11,536	3,220
Unpaid principal balance with related allowance	17,010	5,872
Related allowance	2,365	656
Recorded investment	11,536	3,220
Unpaid principal balance	$ 17,010	$ 5,872

Loans and Leases and the Allo_9

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 757,997	$ 754,780	$ 744,561	$ 747,412
Interest income recognized, Total	11,147	7,013	30,818	19,468
Interest income recognized, Cash basis	8,195	4,333	22,055	11,573
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	204,315	233,572	184,795	205,814
Interest income recognized, Total	1,489	1,425	8,447	3,213
Interest income recognized, Cash basis	1,489	1,425	8,447	3,213
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	256,196	224,526	266,594	242,410
Interest income recognized, Total	1,985	391	4,101	1,674
Interest income recognized, Cash basis	1,985	391	4,101	1,674
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	9,000	8,550	9,111	14,551
Interest income recognized, Total		895	1,682	1,791
Interest income recognized, Cash basis		895	1,682	1,791
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	9,623	16,578	9,056	15,474
Interest income recognized, Total	3,379	25	3,438	958
Interest income recognized, Cash basis	3,379	25	3,438	958
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	133,337	113,892	126,910	108,741
Interest income recognized, Total	1,959	1,903	6,190	5,004
Interest income recognized, Cash basis	773	905	2,612	2,285
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	81,729	91,974	83,700	94,680
Interest income recognized, Total	1,607	1,624	4,763	4,573
Interest income recognized, Cash basis	481	569	1,494	1,292
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	48,542	47,831	48,661	46,829
Interest income recognized, Total	421	419	1,268	1,240
Interest income recognized, Cash basis	62	99	220	290
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	7,805	14,588	11,189	15,483
Interest income recognized, Total	181	251	630	788
Interest income recognized, Cash basis	20	22	49	62
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	7,450	3,269	4,545	3,430
Interest income recognized, Total	126	80	299	227
Interest income recognized, Cash basis	$ 6	$ 2	$ 12	$ 8

Loans and Leases and the All_10

Loans and Leases and the Allowance for Credit Losses - Summary of Loan Grades (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 86,680,485	$ 87,988,983
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,635,394	21,742,651
Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,498,610	20,490,486
Commercial, Financial, Leasing, etc. [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	902,128	1,011,174
Commercial, Financial, Leasing, etc. [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	234,656	240,991
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	25,022,535	25,288,943
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	24,190,472	24,380,184
Commercial [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	624,479	723,777
Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	207,584	184,982
Residential Builder and Developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,643,411	1,631,718
Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,499,791	1,485,148
Residential Builder and Developer [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	140,834	140,119
Residential Builder and Developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,786	6,451
Other Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	6,852,429	6,445,712
Other Commercial Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	6,709,973	6,270,812
Other Commercial Construction [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	123,569	164,812
Other Commercial Construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 18,887	$ 10,088

Loans and Leases and the All_11

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, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	$ 81,669		$ 75,762
Allowance for credit losses	844,624		853,276
Allowance for credit losses	1,019,488	$ 1,019,248	1,017,198	$ 1,013,326	$ 1,008,225	$ 988,997
Purchased Impaired [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	14,910		9,860
Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	941,203		938,898
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	78,285	$ 77,547	78,300	$ 78,212	$ 78,117	$ 78,030
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	46,554		45,488
Allowance for credit losses	270,635		283,111
Commercial, Financial, Leasing, etc. [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	317,189		328,599
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	13,081		10,095
Allowance for credit losses	341,922		363,990
Commercial Real Estate [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	355,003		374,085
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	9,695		7,900
Allowance for credit losses	50,576		47,645
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	14,910		9,860
Residential Real Estate [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	75,181		65,405
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	12,339		12,279
Allowance for credit losses	181,491		158,530
Consumer Loans [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	$ 193,830		$ 170,809

Loans and Leases and the All_12

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, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 86,680,485	$ 87,988,983
Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	792,144	760,309
Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	85,562,361	86,818,659
Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	325,980	410,015
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,635,394	21,742,651
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	255,507	266,376
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,379,887	21,476,254
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount		21
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	33,518,375	33,366,373
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	254,611	226,205
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	33,253,245	33,117,512
Commercial Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,519	22,656
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,721,399	19,613,344
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	218,334	202,163
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,187,604	19,023,843
Residential Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	315,461	387,338
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	13,805,317	13,266,615
Consumer Loans [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	63,692	65,565
Consumer Loans [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 13,741,625	$ 13,201,050

Loans and Leases and the All_13

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, 2018USD ($)Modification	Sep. 30, 2017USD ($)Modification	Sep. 30, 2018USD ($)Modification	Sep. 30, 2017USD ($)Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	151	147	438	506
Pre-modification Recorded Investment	$ 29,537	$ 29,812	$ 157,552	$ 179,726
Post- modification	$ 30,086	$ 29,857	$ 161,617	$ 158,912
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	18	17	66	67
Pre-modification Recorded Investment	$ 11,581	$ 5,861	$ 25,561	$ 38,608
Post- modification	11,265	5,738	25,961	38,393
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	9,992	11,516	80,032	49,250
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	1,493	1,420	14,693	16,193
Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	5		833
Interest Rate Reduction [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			175
Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	3,475	965	9,980	7,818
Other [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	3,475	868	3,869	868
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	16,614	17,376	70,772	101,844
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 6,297	$ 3,450	$ 7,224	$ 21,332
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	47	49	150	162
Pre-modification Recorded Investment	$ 6,837	$ 15,812	$ 96,221	$ 93,346
Post- modification	6,706	15,236	96,884	72,119
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	1,683	5,888	47,029	18,449
Commercial, Financial, Leasing, etc. [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	5		658
Commercial, Financial, Leasing, etc. [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		97	6,111	6,459
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 5,018	$ 9,251	$ 43,086	$ 47,211
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	34	34	111	105
Pre-modification Recorded Investment	$ 8,182	$ 5,123	$ 28,769	$ 22,459
Post- modification	9,028	5,749	31,455	24,165
Residential [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	6,026	3,033	15,785	11,608
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 3,002	$ 2,716	$ 15,670	$ 12,557
Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	2	1	4	6
Pre-modification Recorded Investment	$ 44	$ 5	$ 93	$ 85
Post- modification	44	5	93	85
Other [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 44	$ 5	$ 93	$ 85
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	3	4	8	17
Pre-modification Recorded Investment	$ 716	$ 515	$ 1,595	$ 3,724
Post- modification	847	550	1,890	3,970
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		383	467	618
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 847	$ 167	$ 1,423	$ 3,352
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	17	25	41	85
Pre-modification Recorded Investment	$ 1,651	$ 2,154	$ 3,554	$ 7,885
Post- modification	1,670	2,237	3,581	7,973
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	220	461	224	1,040
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	$ 1,450	$ 1,776	$ 3,357	$ 6,442
Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification				3
Pre-modification Recorded Investment				$ 12,291
Post- modification				10,879
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			1	2
Pre-modification Recorded Investment			$ 752	$ 168
Post- modification			746	168
Other Commercial Construction [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification			$ 746	$ 168
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	30	17	57	59
Pre-modification Recorded Investment	$ 526	$ 342	$ 1,007	$ 1,160
Post- modification	526	342	1,007	1,160
Automobile [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 526	326	995	1,089
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 16	$ 12	$ 71

Borrowings - Additional Informa

Borrowings - Additional Information (Detail) - USD ($) $ in Millions	Jul. 31, 2018	Jan. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Senior notes	$ 750
Debt instrument maturity year	Jul. 31, 2023
Junior subordinated debentures			$ 521
Debt Maturity, Start Year			Jan. 1, 2027
Debt Maturity, End Year			Dec. 31, 2033
Agreements to repurchase securities			$ 412	$ 422
Collateral posted			$ 429	$ 442
Bank Note Program [Member]
Debt Instrument [Line Items]
Senior notes		$ 1,000
Debt instrument maturity year		Jan. 31, 2021
Bank Note Program Fixed Interest Rate [Member]
Debt Instrument [Line Items]
Senior notes		$ 650
Fixed interest rate		2.625%
Fixed Interest Rate [Member]
Debt Instrument [Line Items]
Senior notes	$ 500
Fixed interest rate	3.55%
London Interbank Offered Rate (LIBOR) [Member] | Bank Note Program Variable Interest Rate [Member]
Debt Instrument [Line Items]
Senior notes		$ 350
London Interbank Offered Rate (LIBOR) [Member] | Variable Interest Rate [Member]
Debt Instrument [Line Items]
Senior notes	$ 250

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Detail) - $ / shares	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, par value	$ 1	$ 1
Warrant [Member] | Assumed In Acquisition [Member]
Class of Stock [Line Items]
Exercise price of each class of warrants or rights outstanding	$ 517.01
Warrant to purchase common stock	95,743
Warrants, date of expiration	Dec. 12, 2018

Shareholders' Equity - Issued a

Shareholders' Equity - Issued and Outstanding Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
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_2

Shareholders' Equity - Issued and Outstanding Preferred Stock (Parenthetical) (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
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%
Exercise price of each class of warrants or rights outstanding	$ 73.58
Warrants and rights outstanding	180,491
Warrants, date of expiration	Dec. 23, 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%
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. 1, 2026	Nov. 1, 2026
Preferred Stock, Redemption Feature, Redemption Term	90 days	90 days

Pension Plans and Other Postr_3

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,086	$ 5,048	$ 15,258	$ 15,145
Interest cost on projected benefit obligation	18,676	19,818	56,029	59,452
Expected return on plan assets	(30,781)	(27,131)	(92,344)	(81,393)
Amortization of prior service cost (credit)	139	139	417	418
Amortization of net actuarial loss (gain)	10,948	7,316	32,844	21,947
Net periodic benefit cost	4,068	5,190	12,204	15,569
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	234	293	703	878
Interest cost on projected benefit obligation	573	929	1,719	2,787
Amortization of prior service cost (credit)	(1,182)	(340)	(3,546)	(1,019)
Amortization of net actuarial loss (gain)	(206)	(247)	(619)	(741)
Net periodic benefit cost	$ (581)	$ 635	$ (1,743)	$ 1,905

Pension Plans and Other Postr_4

Pension Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Defined contribution pension and retirement savings plans total expense	$ 16,907,000	$ 16,085,000	$ 55,375,000	$ 53,127,000

Earnings Per Common Share - Com

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income available to common shareholders:
Net income	$ 526,091	$ 355,923	$ 1,371,861	$ 1,085,903
Less: Preferred stock dividends	(18,130)	(18,130)	(54,390)	(54,604)
Net income available to common equity	507,961	337,793	1,317,471	1,031,299
Less: Income attributable to unvested stock-based compensation awards	(2,598)	(1,992)	(6,774)	(6,288)
Net income available to common shareholders	$ 505,363	$ 335,801	$ 1,310,697	$ 1,025,011
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	143,556	152,245	146,177	153,814
Less: Unvested stock-based compensation awards	(734)	(898)	(753)	(948)
Weighted-average shares outstanding	142,822	151,347	145,424	152,866
Basic earnings per common share	$ 3.54	$ 2.22	$ 9.01	$ 6.71

Earnings Per Common Share - C_2

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income available to common equity	$ 507,961	$ 337,793	$ 1,317,471	$ 1,031,299
Less: Income attributable to unvested stock-based compensation awards	(2,596)	(1,989)	(6,768)	(6,276)
Net income available to common shareholders	$ 505,365	$ 335,804	$ 1,310,703	$ 1,025,023
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	143,556	152,245	146,177	153,814
Less: Unvested stock-based compensation awards	(734)	(898)	(753)	(948)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	154	344	181	427
Adjusted weighted-average shares outstanding	142,976	151,691	145,605	153,293
Diluted earnings per common share	$ 3.53	$ 2.21	$ 9	$ 6.69

Earnings Per Common Share - Add

Earnings Per Common Share - Additional Information (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	212,407	408,657	220,653	404,487

Comprehensive Income - Componen

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			$ (493,290)	$ (485,245)
Cumulative effect of change in accounting principles — equity securities, before tax			(22,795)
Unrealized holding gains (losses), before tax			(230,135)	53,221
Foreign currency translation adjustment, before tax			(1,783)	3,829
Unrealized losses on cash flow hedges, before tax			(26,522)	(1,076)
Total other comprehensive income (loss) before reclassifications, before tax			(258,440)	55,974
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			2,519	2,535
(Gains) losses realized in net income, before tax			(18)	17
Accretion of net gain (losses) on terminated cash flow hedges, before tax			(83)	(109)
Net yield adjustment from cash flow hedges currently in effect, before tax			7,650	(2,275)
Amortization of prior service credit, before tax			(3,129)	(601)
Amortization of actuarial losses, before tax			32,225	21,206
Total other comprehensive income (loss), before tax			(219,276)	76,747
Ending balance, before tax	$ (735,361)	$ (408,498)	(735,361)	(408,498)
Beginning balance, tax			129,476	190,609
Cumulative effect of change in accounting principles — equity securities, tax			5,942
Unrealized holding gains (losses), tax			60,494	(20,934)
Foreign currency translation adjustment, tax			374	(1,340)
Unrealized losses on cash flow hedges, tax			6,972	424
Total other comprehensive income (loss) before reclassifications, tax			67,840	(21,850)
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, tax			(662)	(998)
(Gains) losses realized in net income			4	(7)
Accretion of net gain (losses) on terminated cash flow hedges, tax			22	43
Net yield adjustment from cash flow hedges currently in effect, tax			(2,011)	895
Amortization of prior service credit, tax			823	236
Amortization of actuarial losses, tax			(8,472)	(8,345)
Total other comprehensive income (loss), tax			57,544	(30,026)
Ending balance, tax	192,962	160,583	192,962	160,583
Beginning balance, net of tax			(363,814)	(294,636)
Cumulative effect of change in accounting principles- equity securities			(16,853)
Unrealized holding gains (losses), net of tax			(169,641)	32,287
Foreign currency translation adjustment, net of tax	(265)	863	(1,409)	2,489
Unrealized losses on cash flow hedges, net of tax			(19,550)	(652)
Total other comprehensive income (loss) before reclassifications, net of tax			(190,600)	34,124
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, net of tax			1,857	1,537
(Gains) losses realized in net income, net of tax			(14)	10
Accretion of net gain on terminated cash flow hedges, net of tax			(61)	(66)
Net yield adjustment from cash flow hedges currently in effect, net of tax			5,639	(1,380)
Amortization of prior service credit, net of tax			(2,306)	(365)
Amortization of actuarial losses, net of tax			23,753	12,861
Total other comprehensive income (loss)	(24,458)	22,166	(161,732)	46,721
Ending balance, net of tax	(542,399)	(247,915)	(542,399)	(247,915)
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(59,957)
Cumulative effect of change in accounting principles — equity securities, before tax			(22,795)
Unrealized holding gains (losses), before tax			(230,135)
Total other comprehensive income (loss) before reclassifications, before tax			(230,135)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			2,519
(Gains) losses realized in net income, before tax			(18)
Total other comprehensive income (loss), before tax			(227,634)
Ending balance, before tax	(310,386)		(310,386)
Cumulative effect of change in accounting principles- equity securities			(16,853)
Total other comprehensive income (loss)			(167,798)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(413,168)	(449,917)
Amortization of prior service credit, before tax			(3,129)	(601)
Amortization of actuarial losses, before tax			32,225	21,206
Total other comprehensive income (loss), before tax			29,096	20,605
Ending balance, before tax	(384,072)	(429,312)	(384,072)	(429,312)
Total other comprehensive income (loss)			21,447
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(20,165)	(8,268)
Foreign currency translation adjustment, before tax			(1,783)	3,829
Unrealized losses on cash flow hedges, before tax			(26,522)	(1,076)
Total other comprehensive income (loss) before reclassifications, before tax			(28,305)	2,753
Accretion of net gain (losses) on terminated cash flow hedges, before tax			(83)	(109)
Net yield adjustment from cash flow hedges currently in effect, before tax			7,650	(2,275)
Total other comprehensive income (loss), before tax			(20,738)	369
Ending balance, before tax	$ (40,903)	(7,899)	$ (40,903)	(7,899)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax				46,725
Unrealized holding gains (losses), before tax				(7,365)
Total other comprehensive income (loss) before reclassifications, before tax				(7,365)
(Gains) losses realized in net income, before tax				(50)
Total other comprehensive income (loss), before tax				(7,415)
Ending balance, before tax		39,310		39,310
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax				(73,785)
Unrealized holding gains (losses), before tax				60,586
Total other comprehensive income (loss) before reclassifications, before tax				60,586
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax				2,535
(Gains) losses realized in net income, before tax				67
Total other comprehensive income (loss), before tax				63,188
Ending balance, before tax		$ (10,597)		$ (10,597)

Comprehensive Income - Accumula

Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 16,250,819	$ 16,486,622
Cumulative effect of change in accounting principle — equity securities			(16,853)
Net gain (loss) during period	$ (24,458)	$ 22,166	(161,732)	46,721
Ending balance	15,436,085	16,318,052	15,436,085	16,318,052
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(44,150)
Cumulative effect of change in accounting principle — equity securities			(16,853)
Net gain (loss) during period			(167,798)
Ending balance	(228,801)		(228,801)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(304,546)
Net gain (loss) during period			21,447
Ending balance	(283,099)		(283,099)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(15,118)
Net gain (loss) during period			(15,381)
Ending balance	(30,499)		(30,499)
Accumulated Other Comprehensive Income (Loss), Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(363,814)	(294,636)
Cumulative effect of change in accounting principle — equity securities			(16,853)
Net gain (loss) during period			(161,732)
Ending balance	$ (542,399)	$ (247,915)	$ (542,399)	$ (247,915)

Derivative Financial Instrume_3

Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 15,750,000,000		$ 15,750,000,000		$ 9,400,000,000
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans	18,000,000		18,000,000		16,000,000
Aggregate fair value of derivative financial instruments in a liability position	3,000,000		3,000,000		13,000,000
Net liability positions with counterparties	3,000,000		3,000,000		13,000,000
Aggregate fair value of derivative financial instruments in asset position	49,000,000		49,000,000		13,000,000
Net fair value of derivative financial instruments in a net asset position	49,000,000		49,000,000		13,000,000
Collateral relating to net asset positions	46,000,000		46,000,000		12,000,000
Counterparties [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	3,000,000		3,000,000		12,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Amount of initial margin posted	48,000,000		48,000,000		52,000,000
Reduction in the fair value of derivative asset due to contractual settlements			(302,000,000)
Reduction in the fair value of derivative liability due to contractual settlements			(149,000,000)
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase decrease in net interest income due to interest rate swap agreements	(8,000,000)	$ 7,000,000	(12,000,000)	$ 18,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	40,300,000,000		40,300,000,000		29,900,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	869,000,000		869,000,000		$ 530,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Fair value of additional collateral to be posted for derivative financial instruments	$ 0		$ 0

Derivative Financial Instrume_4

Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Amount	$ 15,750,000,000	$ 9,400,000,000
Average Maturity (in years)	1 year 9 months 18 days	2 years 6 months
Estimated Fair Value Gain	$ 2,446,000	$ 639,000
Interest Payments On Variable Rate Commercial Real Estate Loans [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Notional Amount	$ 10,550,000,000	$ 4,850,000,000
Average Maturity (in years)	1 year 4 months 24 days	2 years
Weighted-Average Rate, Fixed	1.52%	1.52%
Weighted-Average Rate, Variable	2.11%	1.36%
Estimated Fair Value Gain	$ 988,000	$ 66,000
Fixed Rate Long-Term Borrowings [Member] | Fair Value Hedges [Member]
Derivative [Line Items]
Notional Amount	$ 5,200,000,000	$ 4,550,000,000
Average Maturity (in years)	2 years 8 months 12 days	2 years 10 months 25 days
Weighted-Average Rate, Fixed	2.45%	2.27%
Weighted-Average Rate, Variable	2.76%	2.09%
Estimated Fair Value Gain	$ 1,458,000	$ 573,000

Derivative Financial Instrume_5

Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Parenthetical) (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Amount	$ 15,750,000,000	$ 9,400,000,000
Forward-Starting Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Notional Amount	7,700,000,000	2,000,000,000
Fair Value Hedges [Member]
Derivative [Line Items]
Reduction of estimated fair value losses on hedging instruments	110,300,000	41,100,000
Cash Flow Hedges [Member]
Derivative [Line Items]
Reduction of estimated fair value losses on hedging instruments	$ 36,100,000	$ 16,300,000

Derivative Financial Instrume_6

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 91,440	$ 92,517
Liability Derivatives, Fair Value	310,968	139,186
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	83,162	91,144
Liability Derivatives, Fair Value	310,422	138,903
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	8,278	1,373
Liability Derivatives, Fair Value	546	283
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	2,446	639
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	5,795	2,526
Liability Derivatives, Fair Value	250	1,019
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	5,832	734
Liability Derivatives, Fair Value	546	283
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	5,625	8,797
Liability Derivatives, Fair Value	1,439	494
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	62,472	74,164
Liability Derivatives, Fair Value	299,791	132,104
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	9,270	5,657
Liability Derivatives, Fair Value	$ 8,942	$ 5,286

Derivative Financial Instrume_7

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Parenthetical) (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Offsetting [Abstract]
Reduction in estimated fair value of interest rate contracts in asset position	$ 302.4	$ 136.2
Reduction in estimated fair value of interest rate contracts in liability position	$ 2.7	$ 12.2

Derivative Financial Instrume_8

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ (566)	$ 944	$ 139	$ 7,129
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	(12,568)	(13,509)	(68,315)	(23,423)
Derivatives in fair value hedging relationships, Hedged item	12,607	14,026	68,861	23,049
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	(1,348)	(418)	(5,639)	2,363
Foreign Exchange and Other Option and Futures Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 782	$ 1,362	$ 5,778	$ 4,766

Derivative Financial Instrume_9

Derivative Financial Instruments - Information about Hedged Items Included in Consolidated Balance Sheet (Detail) - Long-term Debt [Member] - Derivatives Designated and Qualifying as Hedging Instruments [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying Amount [Member]
Derivatives, Fair Value [Line Items]
Hedged Item	$ 5,085,610	$ 4,504,029
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Derivatives, Fair Value [Line Items]
Hedged Item	$ (108,994)	$ (40,133)

Variable Interest Entities an_2

Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Variable Interest Entity Disclosure [Abstract]
Loss on securitization of assets			$ 0	$ 0
Other assets for its "investment" in the common securities recognized by the company of various trusts	$ 23,000,000		23,000,000		$ 23,000,000
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	457,000,000		457,000,000		420,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	215,000,000		215,000,000		$ 201,000,000
Investments amortized to income tax expense	13,000,000	$ 11,000,000	39,000,000	35,000,000
Federal tax credits and other federal tax benefits recognized	$ 15,000,000	$ 16,000,000	$ 47,000,000	$ 47,000,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets	$ 125,038	$ 132,909
Investment securities	9,154,515	10,896,284
U.S. Treasury and Federal Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	1,608,672	1,947,487
Obligations of States and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	1,796	2,589
Government Issued or Guaranteed [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	7,412,696	8,716,392
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	131,328	128,832
Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities		100,956
Fair Value Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets	125,038	132,909
Investment securities	9,154,515	10,896,284
Equity securities	90,129	100,956
Real estate loans held for sale	638,579	378,047
Other assets	19,698	12,696
Total assets	10,027,959	11,419,936
Trading account liabilities	308,733	137,390
Other liabilities	2,235	1,796
Total liabilities	310,968	139,186
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	47,653	47,873
Investment securities		73,232
Equity securities	72,651	73,232
Total assets	120,304	121,105
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	77,385	85,036
Investment securities	9,154,492	10,823,024
Equity securities	17,478	27,724
Real estate loans held for sale	638,579	378,047
Other assets	14,073	3,899
Total assets	9,902,007	11,290,006
Trading account liabilities	308,733	137,390
Other liabilities	796	1,302
Total liabilities	309,529	138,692
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	23	28
Other assets	5,625	8,797
Total assets	5,648	8,825
Other liabilities	1,439	494
Total liabilities	1,439	494
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	1,608,672	1,947,487
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	1,608,672	1,947,487
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	1,796	2,589
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	1,796	2,589
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	7,412,696	8,716,392
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	7,412,696	8,716,392
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	23	28
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	23	28
Fair Value Measurements, Recurring [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	131,328	128,832
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	$ 131,328	$ 128,832

Fair Value Measurements - Chang

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Privately Issued Mortgage-Backed Securities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 24	$ 35	$ 28	$ 44
Total gains (losses) realized/unrealized:
Settlements	(1)	(5)	(5)	(14)
Ending Balance	23	30	23	30
Other Assets and Other Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	10,751	12,425	8,303	7,325
Total gains (losses) realized/unrealized:
Included in earnings	10,284	22,313	38,691	65,824
Transfers out of Level 3	(16,849)	(21,016)	(42,808)	(59,427)
Ending Balance	4,186	13,722	4,186	13,722
Changes in unrealized gains included in earnings related to assets still held at end of period	$ 4,508	$ 12,659	$ 3,663	$ 13,684

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Measurement Input [Extensible List]	us-gaap:MeasurementInputComparabilityAdjustmentMember		us-gaap:MeasurementInputComparabilityAdjustmentMember
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	$ 35	$ 16	$ 69	$ 55
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	292	184	292	184	$ 210
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	32	36	32	36
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	128	105	128	105	145
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	$ 164	$ 79	$ 164	$ 79	$ 65

Fair Value Measurements - Quant

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, 2018	Dec. 31, 2017
Privately Issued Mortgage-Backed Securities [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	$ 23	$ 28
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	$ 4,186	$ 8,303
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	90.00%	78.00%
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	(16.00%)	(22.00%)

Fair Value Measurements - Carry

Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Financial assets:
Interest-bearing deposits at banks	$ 6,523,746		$ 5,078,903
Trading account assets	125,038		132,909
Investment securities	13,073,881		14,664,525
Loans and leases:
Allowance for credit losses	(1,019,488)	$ (1,019,248)	(1,017,198)	$ (1,013,326)	$ (1,008,225)	$ (988,997)
Loans and leases, net	85,660,997		86,971,785
Financial liabilities:
Noninterest-bearing deposits	(31,773,560)		(33,975,180)
Savings and interest-checking deposits	(51,108,962)		(51,698,008)
Time deposits	(5,810,587)		(6,580,962)
Deposits at Cayman Islands office	(447,287)		(177,996)
Long-term borrowings	(9,140,268)		(8,141,430)
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,311,611		1,420,888
Interest-bearing deposits at banks	6,523,746		5,078,903
Trading account assets	125,038		132,909
Investment securities	12,968,432		14,653,074
Loans and leases:
Commercial loans and leases	21,215,945		21,321,282
Commercial real estate loans	32,971,832		32,950,724
Residential real estate loans	17,429,777		19,596,826
Consumer loans	13,676,356		13,161,517
Loans and leases, net	85,293,910		87,030,349
Accrued interest receivable	349,903		327,170
Financial liabilities:
Noninterest-bearing deposits	(31,773,560)		(33,975,180)
Savings and interest-checking deposits	(51,108,962)		(51,698,008)
Time deposits	(5,872,516)		(6,635,048)
Deposits at Cayman Islands office	(447,287)		(177,996)
Short-term borrowings	(1,310,110)		(175,099)
Long-term borrowings	(9,160,009)		(8,193,783)
Accrued interest payable	(68,196)		(75,641)
Trading account liabilities	(308,733)		(137,390)
Other financial instruments:
Commitments to originate real estate loans for sale	4,186		8,303
Commitments to sell real estate loans	10,831		1,958
Other credit-related commitments	(129,102)		(125,281)
Interest rate swap agreements used for interest rate risk management	2,446		639
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,232,393		1,352,035
Trading account assets	47,653		47,873
Investment securities	72,651		73,232
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member] | Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	79,218		68,853
Interest-bearing deposits at banks	6,523,746		5,078,903
Trading account assets	77,385		85,036
Investment securities	12,790,484		14,469,127
Loans and leases:
Commercial real estate loans	381,007		22,130
Residential real estate loans	3,984,387		4,440,645
Loans and leases, net	4,365,394		4,462,775
Accrued interest receivable	349,903		327,170
Financial liabilities:
Noninterest-bearing deposits	(31,773,560)		(33,975,180)
Savings and interest-checking deposits	(51,108,962)		(51,698,008)
Time deposits	(5,872,516)		(6,635,048)
Deposits at Cayman Islands office	(447,287)		(177,996)
Short-term borrowings	(1,310,110)		(175,099)
Long-term borrowings	(9,160,009)		(8,193,783)
Accrued interest payable	(68,196)		(75,641)
Trading account liabilities	(308,733)		(137,390)
Other financial instruments:
Commitments to sell real estate loans	10,831		1,958
Interest rate swap agreements used for interest rate risk management	2,446		639
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Investment securities	105,297		110,715
Loans and leases:
Commercial loans and leases	21,215,945		21,321,282
Commercial real estate loans	32,590,825		32,928,594
Residential real estate loans	13,445,390		15,156,181
Consumer loans	13,676,356		13,161,517
Loans and leases, net	80,928,516		82,567,574
Other financial instruments:
Commitments to originate real estate loans for sale	4,186		8,303
Other credit-related commitments	(129,102)		(125,281)
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,311,611		1,420,888
Interest-bearing deposits at banks	6,523,746		5,078,903
Trading account assets	125,038		132,909
Investment securities	13,073,881		14,664,525
Loans and leases:
Commercial loans and leases	21,635,394		21,742,651
Commercial real estate loans	33,518,375		33,366,373
Residential real estate loans	17,721,399		19,613,344
Consumer loans	13,805,317		13,266,615
Allowance for credit losses	(1,019,488)		(1,017,198)
Loans and leases, net	85,660,997		86,971,785
Accrued interest receivable	349,903		327,170
Financial liabilities:
Noninterest-bearing deposits	(31,773,560)		(33,975,180)
Savings and interest-checking deposits	(51,108,962)		(51,698,008)
Time deposits	(5,810,587)		(6,580,962)
Deposits at Cayman Islands office	(447,287)		(177,996)
Short-term borrowings	(1,310,110)		(175,099)
Long-term borrowings	(9,140,268)		(8,141,430)
Accrued interest payable	(68,196)		(75,641)
Trading account liabilities	(308,733)		(137,390)
Other financial instruments:
Commitments to originate real estate loans for sale	4,186		8,303
Commitments to sell real estate loans	10,831		1,958
Other credit-related commitments	(129,102)		(125,281)
Interest rate swap agreements used for interest rate risk management	$ 2,446		$ 639

Commitments and Contingencies -

Commitments and Contingencies - Company's Significant Commitments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Commitments to extend credit
Home equity lines of credit	$ 5,465,893	$ 5,482,622
Commercial real estate loans to be sold	153,900	194,763
Other commercial real estate	6,549,168	6,050,569
Residential real estate loans to be sold	307,955	347,113
Other residential real estate	267,948	201,426
Commercial and other	14,608,286	12,733,815
Standby letters of credit	2,385,904	2,497,844
Commercial letters of credit	42,030	46,739
Financial guarantees and indemnification contracts	3,416,625	3,434,381
Commitments to sell real estate loans	$ 994,879	$ 812,217

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	$ 3,300,000,000		$ 3,300,000,000
Increase in litigation reserve		$ 135,000,000
Payment of legal settlement expense	200,000,000
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 - Informati

Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 526,091	$ 355,923	$ 1,371,861	$ 1,085,903
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,488,332	1,416,563	4,388,746	4,176,684
Business Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	43,730	31,408	124,455	85,146
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	138,898	130,501	402,811	375,816
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	920	919	2,750	2,836
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	147,910	109,797	399,766	328,211
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	280,671	267,822	816,566	818,846
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	875	840	2,653	2,603
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	116,386	97,295	337,380	269,113
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	214,266	212,014	622,414	604,437
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	371	401	1,096	1,165
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	39,723	31,515	88,575	95,200
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	53,061	65,808	162,075	216,798
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(10,270)	(12,346)	(31,656)	(37,670)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	13,289	13,546	43,637	37,206
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	79,603	90,018	244,228	264,120
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	15,402	18,866	46,870	55,221
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	141,612	96,329	408,081	282,614
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	427,452	392,542	1,241,468	1,144,964
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	2,862	2,668	8,434	8,760
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	23,441	(23,967)	(30,033)	(11,587)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	294,381	257,858	899,184	751,703
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (10,160)	$ (11,348)	$ (30,147)	$ (32,915)

Segment Information - Summary o

Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Segment Reporting Information [Line Items]
Average Total Assets	$ 116,676	$ 120,860	$ 121,073
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	5,637	5,602	5,596
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	26,524	26,573	26,699
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Total Assets	22,899	22,741	22,800
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Total Assets	32,659	37,203	37,807
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	2,123	2,355	2,335
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	13,522	12,702	12,519
All Other [Member]
Segment Reporting Information [Line Items]
Average Total Assets	$ 13,312	$ 13,684	$ 13,317

Segment Information - Summary_2

Segment Information - Summary of Segment Information (Parenthetical) (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting [Abstract]
Taxable-equivalent adjustment	$ 5,733,000	$ 8,828,000	$ 15,939,000	$ 25,563,000

Relationship with Bayview Len_2

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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 9,140,268		$ 9,140,268		$ 8,141,430
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 [Member] | Other Revenues From Operations [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments			24,000
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	2,700,000		2,700,000		3,000,000
Bayview Lending Group and Bayview Financial [Member] | Bank Servicing [Member]
Schedule of Equity Method Investments [Line Items]
Revenue from contract with customer	4,000	$ 4,000	11,000	$ 13,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	60,300,000		60,300,000		56,600,000
Revenues from sub-servicing	28,000	$ 26,000	86,000	$ 74,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	118,000		118,000		$ 136,000
Bayview Financial [Member] | Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	750,000		750,000
Bayview Financial [Member] | Syndicated Loan Facility [Member] | M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 90,000		$ 90,000

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Uncollected amounts receivable	$ 52		$ 52
Accrued interest and other liabilities [Member]
Disaggregation Of Revenue [Line Items]
Deferred revenue	$ 43		$ 43
Maximum [Member]
Disaggregation Of Revenue [Line Items]
Period of satisfaction of contract with customer	1 year		1 year
ASU 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Expense recognized on credit card rewards in other costs of operations	$ 3	$ 3	$ 9	$ 8

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Summary of Sources of M&T's Noninterest Income that are Subject to the Amended Guidance (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Brokerage services income	$ 12,267	$ 14,676	$ 38,288	$ 48,677
Other revenues from operations:
Total other income	459,294	459,429	1,375,404	1,367,090
Service Charges on Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	108,647	109,356	320,546	319,589
Trust Income [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	133,545	$ 124,900	402,561	$ 371,712
ASU 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Brokerage services income	12,267		38,288
Other revenues from operations:
Merchant discount and credit card fees	27,771		78,605
Other	20,906		68,208
Total other income	303,136		908,208
ASU 2014-09 [Member] | Business Banking [Member]
Other revenues from operations:
Merchant discount and credit card fees	9,238		25,075
Total other income	25,005		71,857
ASU 2014-09 [Member] | Commercial Banking [Member]
Other revenues from operations:
Merchant discount and credit card fees	13,520		38,774
Other	1,662		6,871
Total other income	39,349		118,736
ASU 2014-09 [Member] | Commercial Real Estate [Member]
Other revenues from operations:
Merchant discount and credit card fees	643		1,625
Other	1,822		4,896
Total other income	4,839		14,110
ASU 2014-09 [Member] | Discretionary Portfolio [Member]
Other revenues from operations:
Other	386		1,251
Total other income	386		1,251
ASU 2014-09 [Member] | Residential Mortgage Banking [Member]
Other revenues from operations:
Other	916		2,886
Total other income	918		2,894
ASU 2014-09 [Member] | Retail Banking [Member]
Other revenues from operations:
Merchant discount and credit card fees	3,908		11,436
Other	9,397		28,875
Total other income	78,014		228,636
ASU 2014-09 [Member] | All Other [Member]
Disaggregation Of Revenue [Line Items]
Brokerage services income	12,267		38,288
Other revenues from operations:
Merchant discount and credit card fees	462		1,695
Other	6,723		23,429
Total other income	154,625		470,724
ASU 2014-09 [Member] | Service Charges on Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	108,647		320,546
ASU 2014-09 [Member] | Service Charges on Deposit Accounts [Member] | Business Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	15,767		46,782
ASU 2014-09 [Member] | Service Charges on Deposit Accounts [Member] | Commercial Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	24,167		73,091
ASU 2014-09 [Member] | Service Charges on Deposit Accounts [Member] | Commercial Real Estate [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	2,374		7,589
ASU 2014-09 [Member] | Service Charges on Deposit Accounts [Member] | Residential Mortgage Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	2		8
ASU 2014-09 [Member] | Service Charges on Deposit Accounts [Member] | Retail Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	64,709		188,325
ASU 2014-09 [Member] | Service Charges on Deposit Accounts [Member] | All Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	1,628		4,751
ASU 2014-09 [Member] | Trust Income [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	133,545		402,561
ASU 2014-09 [Member] | Trust Income [Member] | All Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contract with customer	$ 133,545		$ 402,561

Recent Accounting Developments

Recent Accounting Developments - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification from accumulated other comprehensive income to retained earnings	$ 17,000,000
ASU 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Lessee, operating lease term		12 months
ASU 2016-02 [Member] | Minimum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Recognizing lease liabilities	385,000,000
ASU 2016-02 [Member] | Maximum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Recognizing lease liabilities	$ 410,000,000