M&T Bank (MTB) 10-Q 4 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
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 Common Stock, Shares Outstanding		145,235,614

Consolidated Balance Sheet (Una

Consolidated Balance Sheet (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 1,291,664	$ 1,420,888
Interest-bearing deposits at banks	6,135,434	5,078,903
Federal funds sold	1,000
Trading account	141,134	132,909
Investment securities (includes pledged securities that can be sold or repledged of $470,906 at March 31, 2018; $487,151 at December 31, 2017)
Available for sale (cost: $10,508,620 at March 31, 2018; $10,938,796 at December 31, 2017)	10,297,856	10,896,284
Held to maturity (fair value: $3,160,215 at March 31, 2018; $3,341,762 at December 31, 2017)	3,228,756	3,353,213
Equity and other securities (cost: $526,593 at March 31, 2018; $415,028 at December 31, 2017)	539,952	415,028
Total investment securities	14,066,564	14,664,525
Loans and leases	87,967,757	88,242,886
Unearned discount	(257,008)	(253,903)
Loans and leases, net of unearned discount	87,710,749	87,988,983
Allowance for credit losses	(1,019,671)	(1,017,198)
Loans and leases, net	86,691,078	86,971,785
Premises and equipment	628,706	646,451
Goodwill	4,593,112	4,593,112
Core deposit and other intangible assets	64,957	71,589
Accrued interest and other assets	5,009,175	5,013,325
Total assets	118,622,824	118,593,487
Liabilities
Noninterest-bearing deposits	31,817,516	33,975,180
Savings and interest-checking deposits	52,724,608	51,698,008
Time deposits	6,126,442	6,580,962
Deposits at Cayman Islands office	278,064	177,996
Total deposits	90,946,630	92,432,146
Short-term borrowings	1,626,129	175,099
Accrued interest and other liabilities	1,749,320	1,593,993
Long-term borrowings	8,591,051	8,141,430
Total liabilities	102,913,130	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 March 31, 2018 and December 31, 2017; Liquidation preference of $10,000 per share: 50,000 shares at March 31, 2018 and December 31, 2017	1,231,500	1,231,500
Common stock, $.50 par, 250,000,000 shares authorized, 159,768,397 shares issued at March 31, 2018; 159,817,518 shares issued at December 31, 2017	79,884	79,909
Common stock issuable, 24,371 shares at March 31, 2018; 27,138 shares at December 31, 2017	1,675	1,847
Additional paid-in capital	6,572,281	6,590,855
Retained earnings	10,404,458	10,164,804
Accumulated other comprehensive income (loss), net	(483,243)	(363,814)
Treasury stock — common, at cost — 12,993,850 shares at March 31, 2018; 9,733,115 shares at December 31, 2017	(2,096,861)	(1,454,282)
Total shareholders’ equity	15,709,694	16,250,819
Total liabilities and shareholders’ equity	$ 118,622,824	$ 118,593,487

Consolidated Balance Sheet (Un3

Consolidated Balance Sheet (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Pledged securities that can be sold or repledged	$ 470,906	$ 487,151
Investment securities, available for sale, amortized cost	10,508,620	10,938,796
Investment securities, held to maturity, fair value	3,160,215	3,341,762
Equity and other securities, cost	$ 526,593	$ 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	159,768,397	159,817,518
Common stock issuable, shares	24,371	27,138
Treasury stock, common shares	12,993,850	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
	Mar. 31, 2018	Mar. 31, 2017
Interest income
Loans and leases, including fees	$ 979,969	$ 898,038
Investment securities
Fully taxable	82,852	95,124
Exempt from federal taxes	248	430
Deposits at banks	18,677	12,162
Other	404	279
Total interest income	1,082,150	1,006,033
Interest expense
Savings and interest-checking deposits	40,527	25,634
Time deposits	10,936	18,998
Deposits at Cayman Islands office	381	265
Short-term borrowings	883	216
Long-term borrowings	53,906	46,660
Total interest expense	106,633	91,773
Net interest income	975,517	914,260
Provision for credit losses	43,000	55,000
Net interest income after provision for credit losses	932,517	859,260
Other income
Mortgage banking revenues	87,306	84,692
Service charges on deposit accounts	105,115	104,176
Trust income	131,375	120,015
Brokerage services income	13,392	17,384
Trading account and foreign exchange gains	4,637	9,691
Gain (loss) on bank investment securities	(9,431)
Other revenues from operations	126,302	110,887
Total other income	458,696	446,845
Other expense
Salaries and employee benefits	463,428	449,741
Equipment and net occupancy	74,797	74,366
Outside data processing and software	48,429	44,301
FDIC assessments	20,280	28,827
Advertising and marketing	16,248	16,110
Printing, postage and supplies	9,319	9,708
Amortization of core deposit and other intangible assets	6,632	8,420
Other costs of operations	294,211	156,379
Total other expense	933,344	787,852
Income before taxes	457,869	518,253
Income taxes	105,259	169,326
Net income	352,610	348,927
Net income available to common shareholders
Basic	332,748	328,562
Diluted	$ 332,749	$ 328,567
Net income per common share
Basic	$ 2.24	$ 2.13
Diluted	2.23	2.12
Cash dividends per common share	$ 0.75	$ 0.75
Average common shares outstanding
Basic	148,688	154,427
Diluted	148,905	154,949

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Partners Capital [Abstract]
Net income	$ 352,610	$ 348,927
Other comprehensive income, net of tax and reclassification adjustments:
Net unrealized gains (losses) on investment securities	(100,684)	(1,356)
Cash flow hedges adjustments	(10,442)	(23)
Foreign currency translation adjustment	1,290	476
Defined benefit plans liability adjustments	7,260	3,972
Total other comprehensive income (loss)	(102,576)	3,069
Total comprehensive income	$ 250,034	$ 351,996

Consolidated Statement of Cash

Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net income	$ 352,610	$ 348,927
Adjustments to reconcile net income to net cash provided by operating activities
Provision for credit losses	43,000	55,000
Depreciation and amortization of premises and equipment	27,281	27,429
Amortization of capitalized servicing rights	11,656	13,543
Amortization of core deposit and other intangible assets	6,632	8,420
Provision for deferred income taxes	(124,772)	36,731
Asset write-downs	3,192	5,118
Net gain on sales of assets	(4,547)	(11,647)
Net change in accrued interest receivable, payable	(14,803)	(23,782)
Net change in other accrued income and expense	165,114	(209)
Net change in loans originated for sale	(72,403)	712,954
Net change in trading account assets and liabilities	91,219	113,332
Net cash provided by operating activities	484,179	1,285,816
Cash flows from investing activities
Proceeds from sales of investment securities Available for sale	100
Proceeds from sales of investment securities Other	254,860	100
Proceeds from maturities of investment securities Available for sale	349,294	697,756
Proceeds from maturities of investment securities Held to maturity	123,923	121,455
Purchases of investment securities Available for sale	(100)	(5,143)
Purchases of investment securities Held to maturity		(539,516)
Purchases of investment securities Other	(288,259)	(278)
Net decrease (increase) in loans and leases	303,886	797,351
Net increase in interest-bearing deposits at banks	(1,056,531)	(1,944,511)
Capital expenditures, net	(9,544)	(21,521)
Net decrease in loan servicing advances	115,163	56,437
Other, net	(41,322)	11,863
Net cash used by investing activities	(248,530)	(826,007)
Net increase (decrease) in deposits	(1,484,629)	1,550,297
Net increase in short-term borrowings	1,451,030	21,660
Proceeds from long-term borrowings	999,594
Payments on long-term borrowings	(504,192)	(1,401,410)
Purchases of treasury stock	(720,966)	(532,073)
Dividends paid - common	(112,318)	(116,566)
Dividends paid - preferred	(17,368)	(17,368)
Other, net	24,976	2,064
Net cash provided (used) by financing activities	(363,873)	(493,396)
Net decrease in cash, cash equivalents and restricted cash	(128,224)	(33,587)
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	1,292,664	1,286,962
Supplemental disclosure of cash flow information
Interest received during the period	1,077,676	1,001,129
Interest paid during the period	118,342	116,183
Income taxes paid during the period	37,999	29,272
Supplemental schedule of noncash investing and financing activities
Real estate acquired in settlement of loans	15,410	23,607
Securitization of residential mortgage loans allocated to Available-for-sale investment securities	5,128	3,684
Securitization of residential mortgage loans allocated to capitalized servicing rights	$ 64	$ 36

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	351,996						348,927	3,069
Preferred stock cash dividends	(18,237)						(18,237)
Exercise of stock warrants into common stock						$ (5,934)				$ 5,934
Purchases of treasury stock	(532,073)								(532,073)
Stock-based compensation plans:
Compensation expense, net	(11,409)		(60)		(67,016)				55,667
Exercises of stock options, net	40,662				(3,127)				43,789
Stock purchase plan	10,831				2,563				8,268
Directors’ stock plan	473				126				347
Deferred compensation plans, net, including dividend equivalents	(54)			(224)	(205)		(21)		396
Common stock cash dividends	(115,707)						(115,707)
Ending balance at Mar. 31, 2017	16,213,104	1,231,500	79,913	1,921	6,603,355		9,437,450	(291,567)	(849,468)
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	250,034						352,610	(102,576)
Preferred stock cash dividends	(18,130)						(18,130)
Exercise of stock warrants into common stock						$ (3,455)				$ 3,455
Purchases of treasury stock	(720,966)								(720,966)
Stock-based compensation plans:
Compensation expense, net	5,833		(25)		(15,362)				21,220
Exercises of stock options, net	42,100				(1,945)				44,045
Stock purchase plan	11,124				2,358				8,766
Directors’ stock plan	589				74				515
Deferred compensation plans, net, including dividend equivalents	(48)			(172)	(244)		(18)		386
Common stock cash dividends	(111,661)						(111,661)
Ending balance at Mar. 31, 2018	$ 15,709,694	$ 1,231,500	$ 79,884	$ 1,675	$ 6,572,281		$ 10,404,458	$ (483,243)	$ (2,096,861)

Consolidated Statement of Chan8

Consolidated Statement of Changes in Shareholders' Equity (Unaudited) (Parenthetical) - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Common stock per share dividend amount	$ 0.75	$ 0.75
Retained Earnings [Member]
Common stock per share dividend amount	$ 0.75	$ 0.75
Series A Warrants [Member] | Treasury Stock [Member]
Exercise of warrants into shares of common stock	36,974	87,515
Exercise of warrants into shares of common stock	22,553	47,954

Significant accounting policies

Significant accounting policies	3 Months Ended
	Mar. 31, 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	3 Months Ended
	Mar. 31, 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 gain (loss) on bank investment securities in the consolidated statement of income during the three months ended March 31, 2018 were $9 million. 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) March 31, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 1,962,160 — 20,682 $ 1,941,478 Obligations of states and political subdivisions 1,986 16 2 2,000 Mortgage-backed securities: Government issued or guaranteed 8,407,476 21,318 206,665 8,222,129 Privately issued 27 — — 27 Other debt securities 136,971 2,457 7,206 132,222 10,508,620 23,791 234,555 10,297,856 Investment securities held to maturity: Obligations of states and political subdivisions 20,209 75 36 20,248 Mortgage-backed securities: Government issued or guaranteed 3,074,830 6,153 58,581 3,022,402 Privately issued 128,997 7,932 24,084 112,845 Other debt securities 4,720 — — 4,720 3,228,756 14,160 82,701 3,160,215 Total debt securities $ 13,737,376 37,951 317,256 $ 13,458,071 Equity and other securities: Readily marketable equity — at fair value 48,358 14,075 716 61,717 Other — at cost 478,235 — — 478,235 Total equity and other securities $ 526,593 14,075 716 $ 539,952 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 quarters ended March 31, 2018 and 2017. At March 31, 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 $ 817,981 813,574 Due after one year through five years 1,151,292 1,134,986 Due after five years through ten years 82,301 82,049 Due after ten years 49,543 45,091 2,101,117 2,075,700 Mortgage-backed securities available for sale 8,407,503 8,222,156 $ 10,508,620 10,297,856 Debt securities held to maturity: Due in one year or less $ 11,410 11,432 Due after one year through five years 8,703 8,716 Due after five years through ten years 96 100 Due after ten years 4,720 4,720 24,929 24,968 Mortgage-backed securities held to maturity 3,203,827 3,135,247 $ 3,228,756 3,160,215 2. Investment securities, continued A summary of investment securities that as of March 31, 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) March 31, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 241,594 (2,314 ) 1,699,784 (18,368 ) Obligations of states and political subdivisions 1,020 (1 ) 376 (1 ) Mortgage-backed securities: Government issued or guaranteed 3,825,869 (68,681 ) 3,023,992 (137,984 ) Other debt securities 4,341 (90 ) 64,506 (7,116 ) 4,072,824 (71,086 ) 4,788,658 (163,469 ) Investment securities held to maturity: Obligations of states and political subdivisions 1,891 (4 ) 5,454 (32 ) Mortgage-backed securities: Government issued or guaranteed 2,280,618 (46,285 ) 249,897 (12,296 ) Privately issued — — 53,852 (24,084 ) 2,282,509 (46,289 ) 309,203 (36,412 ) Total $ 6,355,333 (117,375 ) 5,097,861 (199,881 ) 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 and as of March 31, 2018, 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 1,442 individual debt securities with aggregate gross unrealized losses of $317 million at March 31, 2018. Based on a review of each of the securities in the investment securities portfolio at March 31, 2018, the Company concluded that it expected to recover the amortized cost basis of its investment. As of March 31, 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 March 31, 2018, the Company has not identified events or changes in circumstances which may have a significant adverse effect on the fair value of the $478 million of cost method equity securities.

Loans and leases and the allowa

Loans and leases and the allowance for credit losses	3 Months Ended
	Mar. 31, 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 March 31, 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) March 31, 2018 Commercial, financial, leasing, etc. $ 21,377,917 51,438 5,547 26 2 262,592 $ 21,697,522 Real estate: Commercial 24,919,508 250,993 3,311 4,569 11,744 152,832 25,342,957 Residential builder and developer 1,641,644 1,974 — — 357 4,519 1,648,494 Other commercial construction 6,680,584 71,115 — — 1,194 9,162 6,762,055 Residential 14,942,659 407,773 221,666 8,416 263,939 234,309 16,078,762 Residential — limited documentation 2,599,705 82,738 — — 100,764 98,977 2,882,184 Consumer: Home equity lines and loans 5,037,213 32,100 — 8,157 — 73,169 5,150,639 Automobile 3,468,893 64,995 — — — 20,613 3,554,501 Other 4,523,469 28,686 4,801 28,181 — 8,498 4,593,635 Total $ 85,191,592 991,812 235,325 49,349 378,000 864,671 $ 87,710,749 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 $288 million and $356 million at March 31, 2018 and December 31, 2017, respectively. Commercial real estate loans held for sale were $167 million at March 31, 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: March 31, December 31, 2018 2017 (In thousands) Outstanding principal balance $ 1,305,611 1,394,188 Carrying amount: Commercial, financial, leasing, etc. 28,637 31,105 Commercial real estate 200,932 228,054 Residential real estate 587,562 620,827 Consumer 122,073 123,413 $ 939,204 1,003,399 Purchased impaired loans included in the table above totaled $378 million at March 31, 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-month periods ended March 31, 2018 and 2017 follows: Three Months Ended March 31, 2018 Three Months Ended March 31, 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 (9,819 ) (15,112 ) (10,925 ) (25,518 ) Reclassifications from nonaccretable balance 908 207 146 3,183 Other (a) — (73 ) — 2,492 Balance at end of period $ 149,007 118,184 $ 143,454 181,310 (a) Other changes in expected cash flows including changes in interest rates and prepayment assumptions. Changes in the allowance for credit losses for the three months ended March 31, 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 7,230 (5,225 ) 10,486 29,814 695 43,000 Net charge-offs Charge-offs (14,581 ) (1,366 ) (4,354 ) (36,451 ) — (56,752 ) Recoveries 4,823 223 1,510 9,669 — 16,225 Net charge-offs (9,758 ) (1,143 ) (2,844 ) (26,782 ) — (40,527 ) Ending balance $ 326,071 367,717 73,047 173,841 78,995 $ 1,019,671 3. Loans and leases and the allowance for credit losses, continued Changes in the allowance for credit losses for the three months ended March 31, 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 28,823 1,262 5,637 18,832 446 55,000 Net charge-offs Charge-offs (16,357 ) (5,445 ) (6,259 ) (34,503 ) — (62,564 ) Recoveries 4,461 1,474 1,507 12,555 — 19,997 Net (charge-offs) recoveries (11,896 ) (3,971 ) (4,752 ) (21,948 ) — (42,567 ) Ending balance $ 347,760 360,010 62,012 153,172 78,476 $ 1,001,430 Despite the allocation in the preceding table, 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 The following tables provide information with respect to loans and leases that were considered impaired as of March 31, 2018 and December 31, 2017 and for the three-month periods ended March 31, 2018 and 2017. March 31, 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. $ 172,385 203,464 45,501 177,250 194,257 45,488 Real estate: Commercial 77,118 88,313 9,981 67,199 75,084 9,140 Residential builder and developer 5,536 5,828 187 5,320 5,641 308 Other commercial construction 3,893 19,598 456 4,817 20,357 647 Residential 112,068 134,431 4,048 101,724 122,602 4,000 Residential — limited documentation 76,984 92,586 4,000 77,277 92,439 3,900 Consumer: Home equity lines and loans 48,991 54,032 8,913 48,847 53,914 8,812 Automobile 12,797 15,461 2,694 13,498 15,737 2,811 Other 3,082 5,857 629 3,220 5,872 656 512,854 619,570 76,409 499,152 585,903 75,762 With no related allowance recorded: Commercial, financial, leasing, etc. 115,336 145,450 — 89,126 115,327 — Real estate: Commercial 96,267 104,911 — 138,356 149,716 — Residential builder and developer 3,760 3,832 — 5,057 5,296 — Other commercial construction 5,425 9,142 — 5,456 9,130 — Residential 13,868 19,105 — 13,574 18,980 — Residential — limited documentation 7,751 12,960 — 9,588 16,138 — 242,407 295,400 — 261,157 314,587 — Total: Commercial, financial, leasing, etc. 287,721 348,914 45,501 266,376 309,584 45,488 Real estate: Commercial 173,385 193,224 9,981 205,555 224,800 9,140 Residential builder and developer 9,296 9,660 187 10,377 10,937 308 Other commercial construction 9,318 28,740 456 10,273 29,487 647 Residential 125,936 153,536 4,048 115,298 141,582 4,000 Residential — limited documentation 84,735 105,546 4,000 86,865 108,577 3,900 Consumer: Home equity lines and loans 48,991 54,032 8,913 48,847 53,914 8,812 Automobile 12,797 15,461 2,694 13,498 15,737 2,811 Other 3,082 5,857 629 3,220 5,872 656 Total $ 755,261 914,970 76,409 760,309 900,490 75,762 3. Loans and leases and the allowance for credit losses, continued Three Months Ended March 31, 2018 Three Months Ended March 31, 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. $ 272,172 783 783 271,825 478 478 Real estate: Commercial 181,846 3,147 3,147 182,857 975 975 Residential builder and developer 9,840 1,682 1,682 20,051 429 429 Other commercial construction 10,102 6 6 16,328 847 847 Residential 121,209 1,902 902 103,875 1,636 774 Residential — limited documentation 85,595 1,728 696 97,121 1,500 384 Consumer: Home equity lines and loans 48,797 414 86 45,542 399 100 Automobile 13,125 224 15 16,504 275 19 Other 3,119 85 3 3,598 72 3 Total $ 745,805 9,971 7,320 757,701 6,611 4,009 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. 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) March 31, 2018 Pass $ 20,484,737 24,525,402 1,505,502 6,654,458 Criticized accrual 950,193 664,723 138,473 98,435 Criticized nonaccrual 262,592 152,832 4,519 9,162 Total $ 21,697,522 25,342,957 1,648,494 6,762,055 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 3. Loans and leases and the allowance for credit losses, continued 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 $33 million and $25 million, respectively, at March 31, 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 $19 million and $29 million, respectively, at March 31, 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 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. 3. Loans and leases and the allowance for credit losses, continued The allocation of the allowance for credit losses summarized on the basis of the Company’s impairment methodology was as follows: Commercial, Financial, Real Estate Leasing, etc. Commercial Residential Consumer Total (In thousands) March 31, 2018 Individually evaluated for impairment $ 45,501 10,624 8,048 12,236 $ 76,409 Collectively evaluated for impairment 280,570 357,093 51,093 161,605 850,361 Purchased impaired — — 13,906 — 13,906 Allocated $ 326,071 367,717 73,047 173,841 940,676 Unallocated 78,995 Total $ 1,019,671 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) March 31, 2018 Individually evaluated for impairment $ 287,721 191,999 210,671 64,870 $ 755,261 Collectively evaluated for impairment 21,409,799 33,548,212 18,385,572 13,233,905 86,577,488 Purchased impaired 2 13,295 364,703 — 378,000 Total $ 21,697,522 33,753,506 18,960,946 13,298,775 $ 87,710,749 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 months ended March 31, 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 March 31, 2018 (Dollars in thousands) Commercial, financial, leasing, etc. 56 $ 47,994 $ 35,673 $ 624 $ — $ 13,047 $ 49,344 Real estate: Commercial 20 6,780 5,824 — — 927 6,751 Other commercial construction 1 752 746 — — — 746 Residential 47 12,636 6,945 — — 6,902 13,847 Residential — limited documentation 2 295 267 — — 118 385 Consumer: Home equity lines and loans 14 1,348 4 — — 1,348 1,352 Automobile 8 148 148 — — — 148 Other 2 49 49 — — — 49 Total 150 $ 70,002 $ 49,656 $ 624 $ — $ 22,342 $ 72,622 Three Months Ended March 31, 2017 Commercial, financial, leasing, etc. 50 $ 11,921 $ 4,389 $ — $ 806 $ 2,728 $ 7,923 Real estate: Commercial 20 6,702 2,991 — — 3,606 6,597 Residential builder and developer 3 12,291 — — — 10,879 10,879 Other commercial construction 1 102 102 — — — 102 Residential 41 9,380 5,593 — — 4,355 9,948 Residential — limited documentation 6 1,378 — — — 1,525 1,525 Consumer: Home equity lines and loans 25 2,502 163 — 491 1,848 2,502 Automobile 20 390 383 — — 7 390 Other 2 26 26 — — — 26 Total 168 $ 44,692 $ 13,647 $ — $ 1,297 $ 24,948 $ 39,892 (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. 3. Loans and leases and the allowance for credit losses, continued 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 March 31, 2018 and 2017 and for which there was a subsequent payment default during the three-month periods ended March 31, 2018 and 2017, respectively, were not material. The amount of foreclosed residential real estate property held by the Company was $100 million and $108 million at March 31, 2018 and December 31, 2017, respectively. There were $458 million and $497 million at March 31, 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 March 31, 2018, approximately 41% were classified as purchased impaired and 21% were government guaranteed.

Borrowings

Borrowings	3 Months Ended
	Mar. 31, 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”). M&T had $520 million of fixed and variable rate junior subordinated deferrable interest debentures ("Junior Subordinated Debentures") outstanding at March 31, 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 4. Borrowings, continued 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 $419 million and $422 million at March 31, 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 $436 million and $442 million at March 31, 2018 and December 31, 2017, respectively .

Shareholders' equity

Shareholders' equity	3 Months Ended
	Mar. 31, 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 March 31, 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 $73.75 per share issued in connection with the Series A preferred stock expire on December 23, 2018 and totaled 220,034 at March 31, 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 95,525 shares of M&T common stock at $518.18 per share was outstanding at March 31, 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	3 Months Ended
	Mar. 31, 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 March 31 2018 2017 2018 2017 (In thousands) Service cost $ 5,103 4,908 226 383 Interest cost on projected benefit obligation 18,805 19,691 557 1,080 Expected return on plan assets (30,875 ) (27,200 ) — — Amortization of prior service cost (credit) 125 125 (1,175 ) (350 ) Amortization of net actuarial loss 11,100 6,800 (200 ) (25 ) Net periodic benefit cost $ 4,258 4,324 (592 ) 1,088 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 $21,274,000 and $19,419,000 for the three months ended March 31, 2018 and 2017, respectively, and are included in salaries and employee benefits expense.

Earnings per common share

Earnings per common share	3 Months Ended
	Mar. 31, 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 March 31 2018 2017 (In thousands, except per share) Income available to common shareholders: Net income $ 352,610 348,927 Less: Preferred stock dividends (a) (18,130 ) (18,237 ) Net income available to common equity 334,480 330,690 Less: Income attributable to unvested stock-based compensation awards (1,732 ) (2,128 ) Net income available to common shareholders $ 332,748 328,562 Weighted-average shares outstanding: Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards 149,470 155,463 Less: Unvested stock-based compensation awards (782 ) (1,036 ) Weighted-average shares outstanding 148,688 154,427 Basic earnings per common share $ 2.24 2.13 (a) Including impact of not as yet declared cumulative dividends. 7. Earnings per common share, continued The computations of diluted earnings per common share follow: Three Months Ended March 31 2018 2017 (In thousands, except per share) Net income available to common equity $ 334,480 330,690 Less: Income attributable to unvested stock-based compensation awards (1,731 ) (2,123 ) Net income available to common shareholders $ 332,749 328,567 Adjusted weighted-average shares outstanding: Common and unvested stock-based compensation awards 149,470 155,463 Less: Unvested stock-based compensation awards (782 ) (1,036 ) Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock 217 522 Adjusted weighted-average shares outstanding 148,905 154,949 Diluted earnings per common share $ 2.23 2.12 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 237,584 and 391,764 common shares during the three-month periods ended March 31, 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	3 Months Ended
	Mar. 31, 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 gains (losses), net (145,457 ) — — (145,457 ) 44,176 (101,281 ) Foreign currency translation adjustment — — 1,632 1,632 (342 ) 1,290 Unrealized losses on cash flow hedges — — (14,719 ) (14,719 ) 3,870 (10,849 ) Total other comprehensive income (loss) before reclassifications (145,457 ) — (13,087 ) (158,544 ) 47,704 (110,840 ) Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income: Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities 810 — — 810 (c) (213 ) 597 Accretion of net gain on terminated cash flow hedges — — (28 ) (28 ) (d) 7 (21 ) Net yield adjustment from cash flow hedges currently in effect — — 580 580 (d) (152 ) 428 Amortization of prior service credit — (1,050 ) — (1,050 ) (e) 276 (774 ) Amortization of actuarial losses — 10,900 — 10,900 (e) (2,866 ) 8,034 Total other comprehensive income (loss) (144,647 ) 9,850 (12,535 ) (147,332 ) 44,756 (102,576 ) Balance — March 31, 2018 $ (227,399 ) (403,318 ) (32,700 ) $ (663,417 ) 180,174 $ (483,243 ) 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 (8,628 ) 5,613 — — (3,015 ) 1,182 (1,833 ) Foreign currency translation adjustment — — — 732 732 (256 ) 476 Total other comprehensive income (loss) before reclassifications (8,628 ) 5,613 — 732 (2,283 ) 926 (1,357 ) Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income: Amortization of unrealized holding losses on HTM securities — 787 — — 787 (c) (310 ) 477 Accretion of net gain on terminated cash flow hedges — — — (39 ) (39 ) (d) 16 (23 ) Amortization of prior service credit — — (225 ) — (225 ) (e) 88 (137 ) Amortization of actuarial losses — — 6,775 — 6,775 (e) (2,666 ) 4,109 Total other comprehensive income (loss) (8,628 ) 6,400 6,550 693 5,015 (1,946 ) 3,069 Balance — March 31, 2017 $ 38,097 (67,385 ) (443,367 ) (7,575 ) $ (480,230 ) 188,663 $ (291,567 ) (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. All investment securities with an other-than-temporary impairment charge are within scope of the adopted accounting guidance and no longer require separate presentation. (b) Other-than-temporary impairment (c) Included in interest income (d) Included in interest expense (e) 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 (100,684 ) 7,260 (9,152 ) (102,576 ) Balance — March 31, 2018 $ (161,687 ) (297,286 ) (24,270 ) $ (483,243 )

Derivative financial instrument

Derivative financial instruments	3 Months Ended
	Mar. 31, 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 March 31, 2018. Exclusive of the impact of hedge ineffectiveness (which was not material), the net effect of interest rate swap agreements was to increase net interest income by $1 million and $4 million for the three-month periods ended March 31, 2018 and 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 Gain (a) (In thousands) (In years) (In thousands) March 31, 2018 Fair value hedges: Fixed rate long-term borrowings (b) $ 4,700,000 3.0 2.41 % 2.48 % $ 316 Cash flow hedges: Interest payments on variable rate commercial real estate loans (b)(c) 4,850,000 1.7 1.52 % 1.66 % 60 Total $ 9,550,000 2.5 $ 376 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)(c) 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 March 31, 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 $83.2 million and $41.1 million, respectively, and on interest rate swap agreements designated as cash flow hedges of $30.4 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) 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 $39.5 billion and $29.9 billion at March 31, 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 $538 million and $530 million at March 31, 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 March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 (In thousands) Derivatives designated and qualifying as hedging instruments Interest rate swap agreements (a) $ 376 $ 639 $ — $ — Commitments to sell real estate loans (a) 1,335 734 1,470 283 1,711 1,373 1,470 283 Derivatives not designated and qualifying as hedging instruments Mortgage-related commitments to originate real estate loans for sale (a) 10,562 8,797 1,802 494 Commitments to sell real estate loans (a) 5,361 2,526 2,341 1,019 Trading: Interest rate contracts (b) 71,930 74,164 231,254 132,104 Foreign exchange and other option and futures contracts (b) 6,634 5,657 5,580 5,286 94,487 91,144 240,977 138,903 Total derivatives $ 96,198 $ 92,517 $ 242,447 $ 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 March 31, 2018 and December 31, 2017 was a reduction of the estimated fair value of interest rate contracts in the trading account in an asset position of $235.6 million and $136.2 million, respectively, and in a liability position of $6.2 million and $12.2 million, respectively. Amount of Gain (Loss) Recognized Three Months Ended March 31, 2018 Three Months Ended March 31, 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) $ (42,390 ) 42,370 $ (4,119 ) 4,012 Derivatives not designated as hedging instruments Trading: Interest rate contracts (b) $ (1,605 ) $ 1,950 Foreign exchange and other option and futures contracts (b) 2,631 1,836 Total $ 1,026 $ 3,786 (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. 9. Derivative financial instruments, continued Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount of the Hedged Item March 31, December 31, March 31, December 31, 2018 2017 2018 2017 Location in the Consolidated Balance Sheet of the Hedged Items in Fair Value Hedges Long-term debt $ 4,612,063 $ 4,504,029 $ (82,503 ) $ (40,133 ) The amount of gain (loss) recognized in the consolidated statement of income associated with derivatives designated as cash flow hedges was not material. 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 $17 million and $16 million at March 31, 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. 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 $4 million and $13 million at March 31, 2018 and December 31, 2017, respectively. The Company was required to post collateral relating to those positions of $4 million and $12 million at March 31, 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 March 31, 2018 was not significant. If the credit risk-related contingent features had been triggered on March 31, 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 $38 million and $13 million at March 31, 2018 and December 31, 2017, respectively. 9. Derivative financial instruments, continued 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 $53 million and $52 million at March 31, 2018 and December 31, 2017, respectively. The fair value asset and liability amounts of derivative contracts at March 31, 2018 have been reduced by variation margin payments treated as settlements of $122 million and $6 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	3 Months Ended
	Mar. 31, 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 three-month periods March 31, 2018 and March 31, 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 March 31, 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 March 31, 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 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 $422 million, including $196 million of unfunded commitments, at March 31, 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 March 31, 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 of its investments in qualified affordable housing projects to income tax expense during each of the three-month periods ended March 31, 2018 and 2017 and recognized $16 million of tax credits and other tax benefits during each of those periods. 10. Variable interest entities and asset securitizations, continued 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	3 Months Ended
	Mar. 31, 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 March 31, 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. 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. 11. Fair value measurements, continued 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 March 31, 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) March 31, 2018 Trading account assets $ 141,134 $ 46,215 $ 94,919 $ — Investment securities available for sale: U.S. Treasury and federal agencies 1,941,478 — 1,941,478 — Obligations of states and political subdivisions 2,000 — 2,000 — Mortgage-backed securities: Government issued or guaranteed 8,222,129 — 8,222,129 — Privately issued 27 — — 27 Other debt securities 132,222 — 132,222 — 10,297,856 — 10,297,829 27 Equity securities 61,717 43,496 18,221 — Real estate loans held for sale 455,196 — 455,196 — Other assets (b) 17,634 — 7,072 10,562 Total assets $ 10,973,537 $ 89,711 $ 10,873,237 $ 10,589 Trading account liabilities $ 236,834 $ — $ 236,834 $ - Other liabilities (b) 5,613 — 3,811 1,802 Total liabilities $ 242,447 $ — $ 240,645 $ 1,802 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 three months ended March 31, 2018 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 March 31, 2018 were as follows: Investment Securities Available for S 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 — 8,130 (b) Settlements (1 ) — Transfers in and/or out of Level 3 (a) — (7,673 ) (c) Balance — March 31, 2018 $ 27 8,760 Changes in unrealized gains included in earnings related to assets still held at March 31, 2018 $ — 8,778 (b) The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the three months ended March 31, 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 — 23,940 (b) Settlements (3 ) — Transfers in and/or out of Level 3 (a) — (15,063 ) (c) Balance — March 31, 2017 $ 41 16,202 Changes in unrealized gains included in earnings related to assets still held at March 31, 2017 $ — 15,094 (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 March 31, 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 $178 million at March 31, 2018 ($97 million and $81 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 $210 million at March 31, 2017 ($88 million and $122 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 March 31, 2018 and 2017 were decreases of $27 million and $42 million for the three-month periods ended March 31, 2018 and March 31, 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 $19 million and $32 million at March 31, 2018 and 2017, respectively. Changes in fair value recognized for those foreclosed assets held by the Company were not material during the three-month periods ended March 31, 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 March 31, 2018 and December 31, 2017: Fair Value Valuation Technique Unobservable Inputs/Assumptions Range (Weighted- Average) (In thousands) March 31, 2018 Recurring fair value measurements Privately issued mortgage-backed securities $ 27 Two independent pricing quotes — — Net other assets (liabilities) (a) 8,760 Discounted cash flow Commitment expirations 0%-76% (19%) 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: March 31, 2018 Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 (In thousands) Financial assets: Cash and cash equivalents $ 1,292,664 1,292,664 1,206,172 86,492 — Interest-bearing deposits at banks 6,135,434 6,135,434 — 6,135,434 — Trading account assets 141,134 141,134 46,215 94,919 — Investment securities 14,066,564 13,998,023 43,496 13,841,655 112,872 Loans and leases: Commercial loans and leases 21,697,522 21,294,038 — — 21,294,038 Commercial real estate loans 33,753,506 33,123,306 — 166,773 32,956,533 Residential real estate loans 18,960,946 18,812,289 — 4,226,284 14,586,005 Consumer loans 13,298,775 13,112,874 — — 13,112,874 Allowance for credit losses (1,019,671 ) — — — — Loans and leases, net 86,691,078 86,342,507 — 4,393,057 81,949,450 Accrued interest receivable 332,151 332,151 — 332,151 — Financial liabilities: Noninterest-bearing deposits $ (31,817,516 ) (31,817,516 ) — (31,817,516 ) — Savings and interest-checking deposits (52,724,608 ) (52,724,608 ) — (52,724,608 ) — Time deposits (6,126,442 ) (6,177,695 ) — (6,177,695 ) — Deposits at Cayman Islands office (278,064 ) (278,064 ) — (278,064 ) — Short-term borrowings (1,626,129 ) (1,626,129 ) — (1,626,129 ) — Long-term borrowings (8,591,051 ) (8,598,328 ) — (8,598,328 ) — Accrued interest payable (65,819 ) (65,819 ) — (65,819 ) — Trading account liabilities (236,834 ) (236,834 ) — (236,834 ) — Other financial instruments: Commitments to originate real estate loans for sale $ 8,760 8,760 — — 8,760 Commitments to sell real estate loans 2,885 2,885 — 2,885 — Other credit-related commitments (122,805 ) (122,805 ) — — (122,805 ) Interest rate swap agreements used for interest rate risk management 376 376 — 376 — 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	3 Months Ended
	Mar. 31, 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. March 31, December 31, 2018 2017 (In thousands) Commitments to extend credit Home equity lines of credit $ 5,518,820 5,482,622 Commercial real estate loans to be sold 288,883 194,763 Other commercial real estate 5,788,080 6,050,569 Residential real estate loans to be sold 343,400 347,113 Other residential real estate 223,589 201,426 Commercial and other 12,951,589 12,733,815 Standby letters of credit 2,477,474 2,497,844 Commercial letters of credit 56,245 46,739 Financial guarantees and indemnification contracts 3,449,447 3,434,381 Commitments to sell real estate loans 977,257 812,217 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 March 31, 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 March 31, 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. The agreement in principle is subject to certain required party approvals, the negotiation and execution of a formal settlement agreement and court approval. The Company currently anticipates that necessary party approvals will be completed and a formal settlement agreement will be executed and filed with the court for approval during the second quarter of 2018. A motion for preliminary approval of a proposed settlement will be decided by the court at its discretion. As of March 31, 2018, the Company increased its reserve for litigation matters by $135 million. 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	3 Months Ended
	Mar. 31, 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. During the second quarter of 2017 the Company revised its funds transfer pricing allocation related to certain deposit categories. As a result, financial information for the first quarter of 2017 has been reclassified to provide segment information on a comparable basis, as noted in the following table. 13. Segment information, continued Three Months Ended March 31,2017 Total Revenues as Previously Reported Impact of Changes Total Revenues as Reclassified Net Income (Loss) as Previously Reported Impact of Changes Net Income (Loss) as Reclassified (In thousands) Business Banking $ 115,981 4,352 120,333 $ 22,407 2,581 24,988 Commercial Banking 273,845 63 273,908 112,750 37 112,787 Commercial Real Estate 195,125 — 195,125 84,547 — 84,547 Discretionary Portfolio 78,946 — 78,946 33,945 — 33,945 Residential Mortgage Banking 93,708 (8,307 ) 85,401 14,844 (4,927 ) 9,917 Retail Banking 361,237 7,281 368,518 81,873 4,318 86,191 All Other 242,263 (3,389 ) 238,874 (1,439 ) (2,009 ) (3,448 ) Total $ 1,361,105 — 1,361,105 $ 348,927 — 348,927 Information about the Company's segments is presented in the following table: Three Months Ended March 31 2018 2017 Total Revenues(a) Inter- segment Revenues Net Income (Loss) Total Revenues(a) Inter- segment Revenues Net Income (Loss) (In thousands) Business Banking $ 127,884 918 37,718 $ 120,333 911 24,988 Commercial Banking 266,396 850 125,465 273,908 920 112,787 Commercial Real Estate 202,607 340 108,303 195,125 407 84,547 Discretionary Portfolio 50,038 (10,832 ) 19,739 78,946 (12,927 ) 33,945 Residential 82,458 15,421 14,946 85,401 18,211 9,917 Retail Banking 393,476 2,865 123,380 368,518 3,047 86,191 All Other 311,354 (9,562 ) (76,941 ) 238,874 (10,569 ) (3,448 ) Total $ 1,434,213 — 352,610 $ 1,361,105 — 348,927 13. Segment information, continued Average Total Assets Three Months Ended March 31 Year Ended December 31 2018 2017 2017 (In millions) Business Banking $ 5,681 5,596 5,602 Commercial Banking 26,482 26,723 26,573 Commercial Real Estate 22,811 22,977 22,741 Discretionary Portfolio 34,095 38,731 37,203 Residential Mortgage Banking 2,278 2,426 2,355 Retail Banking 13,377 12,204 12,702 All Other 12,960 14,321 13,684 Total $ 117,684 122,978 120,860 (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 $4,809,000 and $7,999,000 for the three-month periods ended March 31, 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.	3 Months Ended
	Mar. 31, 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 mortgage finance company, is BLG's majority investor. In addition to their common investment in BLG, the Company and Bayview Financial conduct other business activities with each other. The Company has obtained loan servicing rights for mortgage loans from BLG and Bayview Financial having outstanding principal balances of $2.9 billion and $3.0 billion at March 31, 2018 and December 31, 2017, respectively. Revenues from those servicing rights were $4 million for each of the quarters ended March 31, 2018 and 2017. The Company sub-services residential mortgage loans for Bayview Financial having outstanding principal balances of $55.8 billion and $56.6 billion at March 31, 2018 and December 31, 2017, respectively. Revenues earned for sub-servicing loans for Bayview Financial were $30 million and $23 million for the three-month periods ended March 31, 2018 and 2017, respectively. In addition, the Company held $129 million and $136 million of mortgage-backed securities in its held-to-maturity portfolio at March 31, 2018 and December 31, 2017, respectively, that were securitized by Bayview Financial. At March 31, 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	3 Months Ended
	Mar. 31, 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 of rewards in other revenue from operations in the first quarter of 2018. For the quarter ended March 31, 2017, credit card rewards expense of $2 million 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 three months ended March 31, 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 March 31, 2018, the Company had $49 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 March 31, 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 table summarizes sources of M&T’s noninterest income during the first quarter of 2018 that are subject to the amended guidance. 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 $ 15,404 24,654 2,764 — 3 60,601 1,689 $ 105,115 Trust income — — — — — — 131,375 131,375 Brokerage services income — — — — — — 13,392 13,392 Other revenues from operations: Merchant discount and credit card fees 7,503 12,712 554 — — 3,388 615 24,772 Other — 1,563 859 452 1,043 9,865 9,108 22,890 $ 22,907 38,929 4,177 452 1,046 73,854 156,179 $ 297,544 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, 15. Revenue from contracts with customers, continued 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. Merchant discount and other credit card fees include interchange fees and merchant discount fees that are generally recognized as other revenues from operations 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	3 Months Ended
	Mar. 31, 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. 16. Recent accounting developments, continued Standard Description Required date of adoption Effect on consolidated financial statements Standards Adopted in 2018 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. As presented in note 2, fair value changes in such equity securities for the three months ended March 31, 2018 were $9 million and were 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 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 March 31, 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 was committed to $429 million of minimum lease payments under noncancelable operating lease agreements at December 31, 2017. The Company does not expect the new guidance will have a material impact to 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 March 31, 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 assessing the new guidance to determine what modifications to existing credit estimation processes may be required. The Company expects that the new guidance will result in an increase in its allowance for credit losses as a result of considering credit losses over the expected life of its loan portfolios. Increases in the level of allowances will also reflect new requirements to include the nonaccretable principal difference on purchased credit impaired loans and estimated credit losses on investment securities classified as held-to-maturity, if any. The Company is still evaluating the extent of the increase to the allowance for credit losses and the impact to its financial statements. 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.

Significant accounting polici25

Significant accounting policies (Policies)	3 Months Ended
	Mar. 31, 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)	3 Months Ended
	Mar. 31, 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) March 31, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 1,962,160 — 20,682 $ 1,941,478 Obligations of states and political subdivisions 1,986 16 2 2,000 Mortgage-backed securities: Government issued or guaranteed 8,407,476 21,318 206,665 8,222,129 Privately issued 27 — — 27 Other debt securities 136,971 2,457 7,206 132,222 10,508,620 23,791 234,555 10,297,856 Investment securities held to maturity: Obligations of states and political subdivisions 20,209 75 36 20,248 Mortgage-backed securities: Government issued or guaranteed 3,074,830 6,153 58,581 3,022,402 Privately issued 128,997 7,932 24,084 112,845 Other debt securities 4,720 — — 4,720 3,228,756 14,160 82,701 3,160,215 Total debt securities $ 13,737,376 37,951 317,256 $ 13,458,071 Equity and other securities: Readily marketable equity — at fair value 48,358 14,075 716 61,717 Other — at cost 478,235 — — 478,235 Total equity and other securities $ 526,593 14,075 716 $ 539,952 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 March 31, 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 $ 817,981 813,574 Due after one year through five years 1,151,292 1,134,986 Due after five years through ten years 82,301 82,049 Due after ten years 49,543 45,091 2,101,117 2,075,700 Mortgage-backed securities available for sale 8,407,503 8,222,156 $ 10,508,620 10,297,856 Debt securities held to maturity: Due in one year or less $ 11,410 11,432 Due after one year through five years 8,703 8,716 Due after five years through ten years 96 100 Due after ten years 4,720 4,720 24,929 24,968 Mortgage-backed securities held to maturity 3,203,827 3,135,247 $ 3,228,756 3,160,215
Investment Securities in Continuous Unrealized Loss Position	A summary of investment securities that as of March 31, 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) March 31, 2018 Investment securities available for sale: U.S. Treasury and federal agencies $ 241,594 (2,314 ) 1,699,784 (18,368 ) Obligations of states and political subdivisions 1,020 (1 ) 376 (1 ) Mortgage-backed securities: Government issued or guaranteed 3,825,869 (68,681 ) 3,023,992 (137,984 ) Other debt securities 4,341 (90 ) 64,506 (7,116 ) 4,072,824 (71,086 ) 4,788,658 (163,469 ) Investment securities held to maturity: Obligations of states and political subdivisions 1,891 (4 ) 5,454 (32 ) Mortgage-backed securities: Government issued or guaranteed 2,280,618 (46,285 ) 249,897 (12,296 ) Privately issued — — 53,852 (24,084 ) 2,282,509 (46,289 ) 309,203 (36,412 ) Total $ 6,355,333 (117,375 ) 5,097,861 (199,881 ) 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 and as of March 31, 2018, 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 allo27

Loans and leases and the allowance for credit losses (Tables)	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Summary of Current, Past Due and Nonaccrual Loans	A summary of current, past due and nonaccrual loans as of March 31, 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) March 31, 2018 Commercial, financial, leasing, etc. $ 21,377,917 51,438 5,547 26 2 262,592 $ 21,697,522 Real estate: Commercial 24,919,508 250,993 3,311 4,569 11,744 152,832 25,342,957 Residential builder and developer 1,641,644 1,974 — — 357 4,519 1,648,494 Other commercial construction 6,680,584 71,115 — — 1,194 9,162 6,762,055 Residential 14,942,659 407,773 221,666 8,416 263,939 234,309 16,078,762 Residential — limited documentation 2,599,705 82,738 — — 100,764 98,977 2,882,184 Consumer: Home equity lines and loans 5,037,213 32,100 — 8,157 — 73,169 5,150,639 Automobile 3,468,893 64,995 — — — 20,613 3,554,501 Other 4,523,469 28,686 4,801 28,181 — 8,498 4,593,635 Total $ 85,191,592 991,812 235,325 49,349 378,000 864,671 $ 87,710,749 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: March 31, December 31, 2018 2017 (In thousands) Outstanding principal balance $ 1,305,611 1,394,188 Carrying amount: Commercial, financial, leasing, etc. 28,637 31,105 Commercial real estate 200,932 228,054 Residential real estate 587,562 620,827 Consumer 122,073 123,413 $ 939,204 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-month periods ended March 31, 2018 and 2017 follows: Three Months Ended March 31, 2018 Three Months Ended March 31, 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 (9,819 ) (15,112 ) (10,925 ) (25,518 ) Reclassifications from nonaccretable balance 908 207 146 3,183 Other (a) — (73 ) — 2,492 Balance at end of period $ 149,007 118,184 $ 143,454 181,310 (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 March 31, 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 7,230 (5,225 ) 10,486 29,814 695 43,000 Net charge-offs Charge-offs (14,581 ) (1,366 ) (4,354 ) (36,451 ) — (56,752 ) Recoveries 4,823 223 1,510 9,669 — 16,225 Net charge-offs (9,758 ) (1,143 ) (2,844 ) (26,782 ) — (40,527 ) Ending balance $ 326,071 367,717 73,047 173,841 78,995 $ 1,019,671 3. Loans and leases and the allowance for credit losses, continued Changes in the allowance for credit losses for the three months ended March 31, 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 28,823 1,262 5,637 18,832 446 55,000 Net charge-offs Charge-offs (16,357 ) (5,445 ) (6,259 ) (34,503 ) — (62,564 ) Recoveries 4,461 1,474 1,507 12,555 — 19,997 Net (charge-offs) recoveries (11,896 ) (3,971 ) (4,752 ) (21,948 ) — (42,567 ) Ending balance $ 347,760 360,010 62,012 153,172 78,476 $ 1,001,430
Impaired Loans and Leases	The following tables provide information with respect to loans and leases that were considered impaired as of March 31, 2018 and December 31, 2017 and for the three-month periods ended March 31, 2018 and 2017. March 31, 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. $ 172,385 203,464 45,501 177,250 194,257 45,488 Real estate: Commercial 77,118 88,313 9,981 67,199 75,084 9,140 Residential builder and developer 5,536 5,828 187 5,320 5,641 308 Other commercial construction 3,893 19,598 456 4,817 20,357 647 Residential 112,068 134,431 4,048 101,724 122,602 4,000 Residential — limited documentation 76,984 92,586 4,000 77,277 92,439 3,900 Consumer: Home equity lines and loans 48,991 54,032 8,913 48,847 53,914 8,812 Automobile 12,797 15,461 2,694 13,498 15,737 2,811 Other 3,082 5,857 629 3,220 5,872 656 512,854 619,570 76,409 499,152 585,903 75,762 With no related allowance recorded: Commercial, financial, leasing, etc. 115,336 145,450 — 89,126 115,327 — Real estate: Commercial 96,267 104,911 — 138,356 149,716 — Residential builder and developer 3,760 3,832 — 5,057 5,296 — Other commercial construction 5,425 9,142 — 5,456 9,130 — Residential 13,868 19,105 — 13,574 18,980 — Residential — limited documentation 7,751 12,960 — 9,588 16,138 — 242,407 295,400 — 261,157 314,587 — Total: Commercial, financial, leasing, etc. 287,721 348,914 45,501 266,376 309,584 45,488 Real estate: Commercial 173,385 193,224 9,981 205,555 224,800 9,140 Residential builder and developer 9,296 9,660 187 10,377 10,937 308 Other commercial construction 9,318 28,740 456 10,273 29,487 647 Residential 125,936 153,536 4,048 115,298 141,582 4,000 Residential — limited documentation 84,735 105,546 4,000 86,865 108,577 3,900 Consumer: Home equity lines and loans 48,991 54,032 8,913 48,847 53,914 8,812 Automobile 12,797 15,461 2,694 13,498 15,737 2,811 Other 3,082 5,857 629 3,220 5,872 656 Total $ 755,261 914,970 76,409 760,309 900,490 75,762
Interest Income Recognized on Impaired Loans	Three Months Ended March 31, 2018 Three Months Ended March 31, 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. $ 272,172 783 783 271,825 478 478 Real estate: Commercial 181,846 3,147 3,147 182,857 975 975 Residential builder and developer 9,840 1,682 1,682 20,051 429 429 Other commercial construction 10,102 6 6 16,328 847 847 Residential 121,209 1,902 902 103,875 1,636 774 Residential — limited documentation 85,595 1,728 696 97,121 1,500 384 Consumer: Home equity lines and loans 48,797 414 86 45,542 399 100 Automobile 13,125 224 15 16,504 275 19 Other 3,119 85 3 3,598 72 3 Total $ 745,805 9,971 7,320 757,701 6,611 4,009
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) March 31, 2018 Pass $ 20,484,737 24,525,402 1,505,502 6,654,458 Criticized accrual 950,193 664,723 138,473 98,435 Criticized nonaccrual 262,592 152,832 4,519 9,162 Total $ 21,697,522 25,342,957 1,648,494 6,762,055 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) March 31, 2018 Individually evaluated for impairment $ 45,501 10,624 8,048 12,236 $ 76,409 Collectively evaluated for impairment 280,570 357,093 51,093 161,605 850,361 Purchased impaired — — 13,906 — 13,906 Allocated $ 326,071 367,717 73,047 173,841 940,676 Unallocated 78,995 Total $ 1,019,671 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) March 31, 2018 Individually evaluated for impairment $ 287,721 191,999 210,671 64,870 $ 755,261 Collectively evaluated for impairment 21,409,799 33,548,212 18,385,572 13,233,905 86,577,488 Purchased impaired 2 13,295 364,703 — 378,000 Total $ 21,697,522 33,753,506 18,960,946 13,298,775 $ 87,710,749 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 months ended March 31, 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 March 31, 2018 (Dollars in thousands) Commercial, financial, leasing, etc. 56 $ 47,994 $ 35,673 $ 624 $ — $ 13,047 $ 49,344 Real estate: Commercial 20 6,780 5,824 — — 927 6,751 Other commercial construction 1 752 746 — — — 746 Residential 47 12,636 6,945 — — 6,902 13,847 Residential — limited documentation 2 295 267 — — 118 385 Consumer: Home equity lines and loans 14 1,348 4 — — 1,348 1,352 Automobile 8 148 148 — — — 148 Other 2 49 49 — — — 49 Total 150 $ 70,002 $ 49,656 $ 624 $ — $ 22,342 $ 72,622 Three Months Ended March 31, 2017 Commercial, financial, leasing, etc. 50 $ 11,921 $ 4,389 $ — $ 806 $ 2,728 $ 7,923 Real estate: Commercial 20 6,702 2,991 — — 3,606 6,597 Residential builder and developer 3 12,291 — — — 10,879 10,879 Other commercial construction 1 102 102 — — — 102 Residential 41 9,380 5,593 — — 4,355 9,948 Residential — limited documentation 6 1,378 — — — 1,525 1,525 Consumer: Home equity lines and loans 25 2,502 163 — 491 1,848 2,502 Automobile 20 390 383 — — 7 390 Other 2 26 26 — — — 26 Total 168 $ 44,692 $ 13,647 $ — $ 1,297 $ 24,948 $ 39,892 (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)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Issued and Outstanding Preferred Stock	Issued and outstanding preferred stock of M&T as of March 31, 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 $73.75 per share issued in connection with the Series A preferred stock expire on December 23, 2018 and totaled 220,034 at March 31, 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 postr29

Pension plans and other postretirement benefits (Tables)	3 Months Ended
	Mar. 31, 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 March 31 2018 2017 2018 2017 (In thousands) Service cost $ 5,103 4,908 226 383 Interest cost on projected benefit obligation 18,805 19,691 557 1,080 Expected return on plan assets (30,875 ) (27,200 ) — — Amortization of prior service cost (credit) 125 125 (1,175 ) (350 ) Amortization of net actuarial loss 11,100 6,800 (200 ) (25 ) Net periodic benefit cost $ 4,258 4,324 (592 ) 1,088

Earnings per common share (Tabl

Earnings per common share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Computations of Basic Earnings Per Common Share	The computations of basic earnings per common share follow: Three Months Ended March 31 2018 2017 (In thousands, except per share) Income available to common shareholders: Net income $ 352,610 348,927 Less: Preferred stock dividends (a) (18,130 ) (18,237 ) Net income available to common equity 334,480 330,690 Less: Income attributable to unvested stock-based compensation awards (1,732 ) (2,128 ) Net income available to common shareholders $ 332,748 328,562 Weighted-average shares outstanding: Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards 149,470 155,463 Less: Unvested stock-based compensation awards (782 ) (1,036 ) Weighted-average shares outstanding 148,688 154,427 Basic earnings per common share $ 2.24 2.13 (a) Including impact of not as yet declared cumulative dividends.
Computations of Diluted Earnings Per Common Share	7. Earnings per common share, continued The computations of diluted earnings per common share follow: Three Months Ended March 31 2018 2017 (In thousands, except per share) Net income available to common equity $ 334,480 330,690 Less: Income attributable to unvested stock-based compensation awards (1,731 ) (2,123 ) Net income available to common shareholders $ 332,749 328,567 Adjusted weighted-average shares outstanding: Common and unvested stock-based compensation awards 149,470 155,463 Less: Unvested stock-based compensation awards (782 ) (1,036 ) Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock 217 522 Adjusted weighted-average shares outstanding 148,905 154,949 Diluted earnings per common share $ 2.23 2.12

Comprehensive income (Tables)

Comprehensive income (Tables)	3 Months Ended
	Mar. 31, 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 gains (losses), net (145,457 ) — — (145,457 ) 44,176 (101,281 ) Foreign currency translation adjustment — — 1,632 1,632 (342 ) 1,290 Unrealized losses on cash flow hedges — — (14,719 ) (14,719 ) 3,870 (10,849 ) Total other comprehensive income (loss) before reclassifications (145,457 ) — (13,087 ) (158,544 ) 47,704 (110,840 ) Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income: Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities 810 — — 810 (c) (213 ) 597 Accretion of net gain on terminated cash flow hedges — — (28 ) (28 ) (d) 7 (21 ) Net yield adjustment from cash flow hedges currently in effect — — 580 580 (d) (152 ) 428 Amortization of prior service credit — (1,050 ) — (1,050 ) (e) 276 (774 ) Amortization of actuarial losses — 10,900 — 10,900 (e) (2,866 ) 8,034 Total other comprehensive income (loss) (144,647 ) 9,850 (12,535 ) (147,332 ) 44,756 (102,576 ) Balance — March 31, 2018 $ (227,399 ) (403,318 ) (32,700 ) $ (663,417 ) 180,174 $ (483,243 ) 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 (8,628 ) 5,613 — — (3,015 ) 1,182 (1,833 ) Foreign currency translation adjustment — — — 732 732 (256 ) 476 Total other comprehensive income (loss) before reclassifications (8,628 ) 5,613 — 732 (2,283 ) 926 (1,357 ) Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income: Amortization of unrealized holding losses on HTM securities — 787 — — 787 (c) (310 ) 477 Accretion of net gain on terminated cash flow hedges — — — (39 ) (39 ) (d) 16 (23 ) Amortization of prior service credit — — (225 ) — (225 ) (e) 88 (137 ) Amortization of actuarial losses — — 6,775 — 6,775 (e) (2,666 ) 4,109 Total other comprehensive income (loss) (8,628 ) 6,400 6,550 693 5,015 (1,946 ) 3,069 Balance — March 31, 2017 $ 38,097 (67,385 ) (443,367 ) (7,575 ) $ (480,230 ) 188,663 $ (291,567 ) (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. All investment securities with an other-than-temporary impairment charge are within scope of the adopted accounting guidance and no longer require separate presentation. (b) Other-than-temporary impairment (c) Included in interest income (d) Included in interest expense (e) 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 (100,684 ) 7,260 (9,152 ) (102,576 ) Balance — March 31, 2018 $ (161,687 ) (297,286 ) (24,270 ) $ (483,243 )

Derivative financial instrume32

Derivative financial instruments (Tables)	3 Months Ended
	Mar. 31, 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 Gain (a) (In thousands) (In years) (In thousands) March 31, 2018 Fair value hedges: Fixed rate long-term borrowings (b) $ 4,700,000 3.0 2.41 % 2.48 % $ 316 Cash flow hedges: Interest payments on variable rate commercial real estate loans (b)(c) 4,850,000 1.7 1.52 % 1.66 % 60 Total $ 9,550,000 2.5 $ 376 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)(c) 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 March 31, 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 $83.2 million and $41.1 million, respectively, and on interest rate swap agreements designated as cash flow hedges of $30.4 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)
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 March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 (In thousands) Derivatives designated and qualifying as hedging instruments Interest rate swap agreements (a) $ 376 $ 639 $ — $ — Commitments to sell real estate loans (a) 1,335 734 1,470 283 1,711 1,373 1,470 283 Derivatives not designated and qualifying as hedging instruments Mortgage-related commitments to originate real estate loans for sale (a) 10,562 8,797 1,802 494 Commitments to sell real estate loans (a) 5,361 2,526 2,341 1,019 Trading: Interest rate contracts (b) 71,930 74,164 231,254 132,104 Foreign exchange and other option and futures contracts (b) 6,634 5,657 5,580 5,286 94,487 91,144 240,977 138,903 Total derivatives $ 96,198 $ 92,517 $ 242,447 $ 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 March 31, 2018 and December 31, 2017 was a reduction of the estimated fair value of interest rate contracts in the trading account in an asset position of $235.6 million and $136.2 million, respectively, and in a liability position of $6.2 million and $12.2 million, respectively. 9. Derivative financial instruments, continued Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount of the Hedged Item March 31, December 31, March 31, December 31, 2018 2017 2018 2017 Location in the Consolidated Balance Sheet of the Hedged Items in Fair Value Hedges Long-term debt $ 4,612,063 $ 4,504,029 $ (82,503 ) $ (40,133 )
Information about Fair Values of Derivative Instruments in Consolidated Statement of Income	Amount of Gain (Loss) Recognized Three Months Ended March 31, 2018 Three Months Ended March 31, 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) $ (42,390 ) 42,370 $ (4,119 ) 4,012 Derivatives not designated as hedging instruments Trading: Interest rate contracts (b) $ (1,605 ) $ 1,950 Foreign exchange and other option and futures contracts (b) 2,631 1,836 Total $ 1,026 $ 3,786 (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)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis	The following tables present assets and liabilities at March 31, 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) March 31, 2018 Trading account assets $ 141,134 $ 46,215 $ 94,919 $ — Investment securities available for sale: U.S. Treasury and federal agencies 1,941,478 — 1,941,478 — Obligations of states and political subdivisions 2,000 — 2,000 — Mortgage-backed securities: Government issued or guaranteed 8,222,129 — 8,222,129 — Privately issued 27 — — 27 Other debt securities 132,222 — 132,222 — 10,297,856 — 10,297,829 27 Equity securities 61,717 43,496 18,221 — Real estate loans held for sale 455,196 — 455,196 — Other assets (b) 17,634 — 7,072 10,562 Total assets $ 10,973,537 $ 89,711 $ 10,873,237 $ 10,589 Trading account liabilities $ 236,834 $ — $ 236,834 $ - Other liabilities (b) 5,613 — 3,811 1,802 Total liabilities $ 242,447 $ — $ 240,645 $ 1,802 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 three months ended March 31, 2018 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 March 31, 2018 were as follows: Investment Securities Available for S 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 — 8,130 (b) Settlements (1 ) — Transfers in and/or out of Level 3 (a) — (7,673 ) (c) Balance — March 31, 2018 $ 27 8,760 Changes in unrealized gains included in earnings related to assets still held at March 31, 2018 $ — 8,778 (b) The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the three months ended March 31, 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 — 23,940 (b) Settlements (3 ) — Transfers in and/or out of Level 3 (a) — (15,063 ) (c) Balance — March 31, 2017 $ 41 16,202 Changes in unrealized gains included in earnings related to assets still held at March 31, 2017 $ — 15,094 (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 March 31, 2018 and December 31, 2017: Fair Value Valuation Technique Unobservable Inputs/Assumptions Range (Weighted- Average) (In thousands) March 31, 2018 Recurring fair value measurements Privately issued mortgage-backed securities $ 27 Two independent pricing quotes — — Net other assets (liabilities) (a) 8,760 Discounted cash flow Commitment expirations 0%-76% (19%) 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: March 31, 2018 Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 (In thousands) Financial assets: Cash and cash equivalents $ 1,292,664 1,292,664 1,206,172 86,492 — Interest-bearing deposits at banks 6,135,434 6,135,434 — 6,135,434 — Trading account assets 141,134 141,134 46,215 94,919 — Investment securities 14,066,564 13,998,023 43,496 13,841,655 112,872 Loans and leases: Commercial loans and leases 21,697,522 21,294,038 — — 21,294,038 Commercial real estate loans 33,753,506 33,123,306 — 166,773 32,956,533 Residential real estate loans 18,960,946 18,812,289 — 4,226,284 14,586,005 Consumer loans 13,298,775 13,112,874 — — 13,112,874 Allowance for credit losses (1,019,671 ) — — — — Loans and leases, net 86,691,078 86,342,507 — 4,393,057 81,949,450 Accrued interest receivable 332,151 332,151 — 332,151 — Financial liabilities: Noninterest-bearing deposits $ (31,817,516 ) (31,817,516 ) — (31,817,516 ) — Savings and interest-checking deposits (52,724,608 ) (52,724,608 ) — (52,724,608 ) — Time deposits (6,126,442 ) (6,177,695 ) — (6,177,695 ) — Deposits at Cayman Islands office (278,064 ) (278,064 ) — (278,064 ) — Short-term borrowings (1,626,129 ) (1,626,129 ) — (1,626,129 ) — Long-term borrowings (8,591,051 ) (8,598,328 ) — (8,598,328 ) — Accrued interest payable (65,819 ) (65,819 ) — (65,819 ) — Trading account liabilities (236,834 ) (236,834 ) — (236,834 ) — Other financial instruments: Commitments to originate real estate loans for sale $ 8,760 8,760 — — 8,760 Commitments to sell real estate loans 2,885 2,885 — 2,885 — Other credit-related commitments (122,805 ) (122,805 ) — — (122,805 ) Interest rate swap agreements used for interest rate risk management 376 376 — 376 — 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)	3 Months Ended
	Mar. 31, 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. March 31, December 31, 2018 2017 (In thousands) Commitments to extend credit Home equity lines of credit $ 5,518,820 5,482,622 Commercial real estate loans to be sold 288,883 194,763 Other commercial real estate 5,788,080 6,050,569 Residential real estate loans to be sold 343,400 347,113 Other residential real estate 223,589 201,426 Commercial and other 12,951,589 12,733,815 Standby letters of credit 2,477,474 2,497,844 Commercial letters of credit 56,245 46,739 Financial guarantees and indemnification contracts 3,449,447 3,434,381 Commitments to sell real estate loans 977,257 812,217

Segment information (Tables)

Segment information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Summary of Reclassified Segment Information on Comparable Basis	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. During the second quarter of 2017 the Company revised its funds transfer pricing allocation related to certain deposit categories. As a result, financial information for the first quarter of 2017 has been reclassified to provide segment information on a comparable basis, as noted in the following table. 13. Segment information, continued Three Months Ended March 31,2017 Total Revenues as Previously Reported Impact of Changes Total Revenues as Reclassified Net Income (Loss) as Previously Reported Impact of Changes Net Income (Loss) as Reclassified (In thousands) Business Banking $ 115,981 4,352 120,333 $ 22,407 2,581 24,988 Commercial Banking 273,845 63 273,908 112,750 37 112,787 Commercial Real Estate 195,125 — 195,125 84,547 — 84,547 Discretionary Portfolio 78,946 — 78,946 33,945 — 33,945 Residential Mortgage Banking 93,708 (8,307 ) 85,401 14,844 (4,927 ) 9,917 Retail Banking 361,237 7,281 368,518 81,873 4,318 86,191 All Other 242,263 (3,389 ) 238,874 (1,439 ) (2,009 ) (3,448 ) Total $ 1,361,105 — 1,361,105 $ 348,927 — 348,927
Information about Company's Segments	Information about the Company's segments is presented in the following table: Three Months Ended March 31 2018 2017 Total Revenues(a) Inter- segment Revenues Net Income (Loss) Total Revenues(a) Inter- segment Revenues Net Income (Loss) (In thousands) Business Banking $ 127,884 918 37,718 $ 120,333 911 24,988 Commercial Banking 266,396 850 125,465 273,908 920 112,787 Commercial Real Estate 202,607 340 108,303 195,125 407 84,547 Discretionary Portfolio 50,038 (10,832 ) 19,739 78,946 (12,927 ) 33,945 Residential 82,458 15,421 14,946 85,401 18,211 9,917 Retail Banking 393,476 2,865 123,380 368,518 3,047 86,191 All Other 311,354 (9,562 ) (76,941 ) 238,874 (10,569 ) (3,448 ) Total $ 1,434,213 — 352,610 $ 1,361,105 — 348,927 13. Segment information, continued Average Total Assets Three Months Ended March 31 Year Ended December 31 2018 2017 2017 (In millions) Business Banking $ 5,681 5,596 5,602 Commercial Banking 26,482 26,723 26,573 Commercial Real Estate 22,811 22,977 22,741 Discretionary Portfolio 34,095 38,731 37,203 Residential Mortgage Banking 2,278 2,426 2,355 Retail Banking 13,377 12,204 12,702 All Other 12,960 14,321 13,684 Total $ 117,684 122,978 120,860 (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 $4,809,000 and $7,999,000 for the three-month periods ended March 31, 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 C36

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2018
ASU 2014-09 [Member]
Summary of Sources of M&T's Noninterest Income that are Subject to the Amended Guidance	The following table summarizes sources of M&T’s noninterest income during the first quarter of 2018 that are subject to the amended guidance. 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 $ 15,404 24,654 2,764 — 3 60,601 1,689 $ 105,115 Trust income — — — — — — 131,375 131,375 Brokerage services income — — — — — — 13,392 13,392 Other revenues from operations: Merchant discount and credit card fees 7,503 12,712 554 — — 3,388 615 24,772 Other — 1,563 859 452 1,043 9,865 9,108 22,890 $ 22,907 38,929 4,177 452 1,046 73,854 156,179 $ 297,544

Investment Securities - Additio

Investment Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018USD ($)Security	Mar. 31, 2017USD ($)
Investment Holdings [Line Items]
Gain (loss) on bank investment securities	$ (9,431,000)
Gross realized gains(loss) on sale of investment securities	$ 0	$ 0
Number of debt securities with aggregate gross unrealized losses | Security	1,442
Unrealized losses on individual debt securities	$ 317,000,000
Cost method equity securities	478,000,000
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

Investment Securities - Amortiz

Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	$ 10,508,620	$ 10,938,796
Investment securities available for sale, gross unrealized gains	23,791	85,154
Investment securities available for sale, gross unrealized losses	234,555	127,666
Investment securities available for sale, estimated fair value	10,297,856	10,896,284
Amortized cost for held to maturity	3,228,756	3,353,213
Gross unrealized gains for held to maturity	14,160	29,919
Gross unrealized losses for held to maturity	82,701	41,370
Estimated fair value for held to maturity	3,160,215	3,341,762
Equity and other securities, Amortized Cost	526,593	415,028
Equity securities, Gross Unrealized Gains	14,075
Equity securities, Gross Unrealized Losses	716
Equity and other securities, Estimated Fair Value	539,952	415,028
Other securities, Amortized cost	478,235	415,028
Other securities, Estimated fair value	478,235	415,028
Total debt securities Amortized cost	13,737,376
Total debt securities Gross unrealized gains	37,951
Total debt securities Gross unrealized losses	317,256
Total debt securities Estimated fair value	13,458,071
Readily marketable securities Amortized cost	48,358
Readily marketable securities Gross unrealized gains	14,075
Readily marketable securities Gross unrealized losses	716
Readily marketable securities Estimated fair value	61,717
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	1,962,160	1,965,665
Investment securities available for sale, gross unrealized losses	20,682	18,178
Investment securities available for sale, estimated fair value	1,941,478	1,947,487
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	1,986	2,555
Investment securities available for sale, gross unrealized gains	16	36
Investment securities available for sale, gross unrealized losses	2	2
Investment securities available for sale, estimated fair value	2,000	2,589
Amortized cost for held to maturity	20,209	24,562
Gross unrealized gains for held to maturity	75	109
Gross unrealized losses for held to maturity	36	49
Estimated fair value for held to maturity	20,248	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	8,407,476	8,755,482
Investment securities available for sale, gross unrealized gains	21,318	59,497
Investment securities available for sale, gross unrealized losses	206,665	98,587
Investment securities available for sale, estimated fair value	8,222,129	8,716,392
Amortized cost for held to maturity	3,074,830	3,187,953
Gross unrealized gains for held to maturity	6,153	27,236
Gross unrealized losses for held to maturity	58,581	13,746
Estimated fair value for held to maturity	3,022,402	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	27	28
Investment securities available for sale, estimated fair value	27	28
Amortized cost for held to maturity	128,997	135,688
Gross unrealized gains for held to maturity	7,932	2,574
Gross unrealized losses for held to maturity	24,084	27,575
Estimated fair value for held to maturity	112,845	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	136,971	136,905
Investment securities available for sale, gross unrealized gains	2,457	2,402
Investment securities available for sale, gross unrealized losses	7,206	10,475
Investment securities available for sale, estimated fair value	132,222	128,832
Amortized cost for held to maturity	4,720	5,010
Estimated fair value for held to maturity	$ 4,720	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 - Amort39

Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt securities available for sale:
Due in one year or less	$ 817,981
Due after one year through five years	1,151,292
Due after five years through ten years	82,301
Due after ten years	49,543
Total available for sale (amortized cost)	2,101,117
Mortgage-backed securities available for sale	8,407,503
Total	10,508,620
Debt securities held to maturity:
Due in one year or less	11,410
Due after one year through five years	8,703
Due after five years through ten years	96
Due after ten years	4,720
Total available for held to maturity (amortized cost)	24,929
Mortgage-backed securities held to maturity	3,203,827
Amortized cost for held to maturity	3,228,756	$ 3,353,213
Debt securities available for sale:
Due in one year or less	813,574
Due after one year through five years	1,134,986
Due after five years through ten years	82,049
Due after ten years	45,091
Total available for sale (fair value)	2,075,700
Mortgage-backed securities available for sale	8,222,156
Total	10,297,856
Debt securities held to maturity:
Due in one year or less	11,432
Due after one year through five years	8,716
Due after five years through ten years	100
Due after ten years	4,720
Total available for held to maturity (fair value)	24,968
Mortgage-backed securities held to maturity	3,135,247
Total	$ 3,160,215	$ 3,341,762

Investment Securities - Investm

Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	$ 4,072,824	$ 2,387,341
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(71,086)	(15,482)
Estimated fair value, 12 months or more	4,788,658	4,887,991
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(163,469)	(112,184)
Held to maturity, Estimated fair value, Less than 12 months	2,282,509	1,339,774
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(46,289)	(8,256)
Held to maturity, Estimated fair value, 12 months or more	309,203	327,060
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(36,412)	(33,114)
Total investment securities, fair value less than 12 months	6,355,333	3,727,115
Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses	(117,375)	(23,738)
Total of investment securities, fair value, 12 Months or More	5,097,861	5,215,051
Investment Securities Continuous Unrealized Loss Position Twelve Months or Longer Aggregate Losses	(199,881)	(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	241,594	278,132
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(2,314)	(1,761)
Estimated fair value, 12 months or more	1,699,784	1,669,355
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(18,368)	(16,417)
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	1,020
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(1)
Estimated fair value, 12 months or more	376	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	1,891	2,954
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(4)	(4)
Held to maturity, Estimated fair value, 12 months or more	5,454	6,110
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(32)	(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	3,825,869	2,106,142
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(68,681)	(13,695)
Estimated fair value, 12 months or more	3,023,992	3,138,841
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(137,984)	(84,892)
Held to maturity, Estimated fair value, Less than 12 months	2,280,618	1,331,759
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(46,285)	(7,036)
Held to maturity, Estimated fair value, 12 months or more	249,897	265,695
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(12,296)	(6,710)
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	4,341	3,067
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(90)	(26)
Estimated fair value, 12 months or more	64,506	61,159
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(7,116)	(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)
Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Held to maturity, Estimated fair value, Less than 12 months		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	53,852	55,255
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	$ (24,084)	$ (26,359)

Loans and Leases and the Allo41

Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$ 85,191,592	$ 85,325,604
30-89 Days Past Due	991,812	1,078,943
Accruing Loans Past Due 90 Days or More	235,325	244,405
Purchased Impaired	378,000	410,015
Nonaccrual	864,671	882,598
Loans and leases, net of unearned discount	87,710,749	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	49,349	47,418
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	21,377,917	21,332,234
30-89 Days Past Due	51,438	167,756
Accruing Loans Past Due 90 Days or More	5,547	1,322
Purchased Impaired	2	21
Nonaccrual	262,592	240,991
Loans and leases, net of unearned discount	21,697,522	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	26	327
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	24,919,508	24,910,381
30-89 Days Past Due	250,993	166,305
Accruing Loans Past Due 90 Days or More	3,311	4,444
Purchased Impaired	11,744	16,815
Nonaccrual	152,832	184,982
Loans and leases, net of unearned discount	25,342,957	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	4,569	6,016
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,641,644	1,618,973
30-89 Days Past Due	1,974	5,159
Purchased Impaired	357	1,135
Nonaccrual	4,519	6,451
Loans and leases, net of unearned discount	1,648,494	1,631,718
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	6,680,584	6,407,451
30-89 Days Past Due	71,115	23,467
Purchased Impaired	1,194	4,706
Nonaccrual	9,162	10,088
Loans and leases, net of unearned discount	6,762,055	6,445,712
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	14,942,659	15,376,759
30-89 Days Past Due	407,773	474,372
Accruing Loans Past Due 90 Days or More	221,666	233,437
Purchased Impaired	263,939	282,102
Nonaccrual	234,309	235,834
Loans and leases, net of unearned discount	16,078,762	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	8,416	7,582
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,599,705	2,718,019
30-89 Days Past Due	82,738	83,898
Purchased Impaired	100,764	105,236
Nonaccrual	98,977	96,105
Loans and leases, net of unearned discount	2,882,184	3,003,258
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,037,213	5,171,345
30-89 Days Past Due	32,100	38,546
Nonaccrual	73,169	74,500
Loans and leases, net of unearned discount	5,150,639	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	8,157	9,391
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,468,893	3,441,371
30-89 Days Past Due	64,995	78,511
Nonaccrual	20,613	23,781
Loans and leases, net of unearned discount	3,554,501	3,543,663
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	4,523,469	4,349,071
30-89 Days Past Due	28,686	40,929
Accruing Loans Past Due 90 Days or More	4,801	5,202
Nonaccrual	8,498	9,866
Loans and leases, net of unearned discount	4,593,635	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	$ 28,181	$ 24,102

Loans and Leases and the Allo42

Loans and Leases and the Allowance for Credit Losses - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Loans And Leases Receivable [Line Items]
Commercial real estate loans held for sale	$ 167	$ 22
Contractual principal and interest payments	$ 378	410
Minimum delinquency period for loan level collectability analysis consumer mortgage	150 days
Amount of foreclosed residential real estate property held	$ 100	108
Loans secured by residential real estate that were in the process of foreclosure	$ 458	497
Percentage loans in the process of foreclosure, serviced by other entities, classified as purchased impaired	41.00%
Percentage loans in the process of foreclosure, serviced by other entities, classified as government guaranteed	21.00%
Residential Mortgage Loans [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	$ 288	356
Carrying value of loans for which partial charge-off has been recognized	33	34
Mortgage loans on real real estate not requiring charge off due to collateral carrying amount	19	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	25	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 Allo43

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	Mar. 31, 2018	Dec. 31, 2017
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$ 1,305,611	$ 1,394,188
Carrying amount	939,204	1,003,399
Commercial, Financial, Leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	28,637	31,105
Commercial Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	200,932	228,054
Residential Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	587,562	620,827
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$ 122,073	$ 123,413

Loans and Leases and the Allo44

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
	Mar. 31, 2018	Mar. 31, 2017
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 157,918	$ 154,233
Interest income	(9,819)	(10,925)
Reclassifications from nonaccretable balance	908	146
Balance at end of period	149,007	143,454
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	133,162	201,153
Interest income	(15,112)	(25,518)
Reclassifications from nonaccretable balance	207	3,183
Other	(73)	2,492
Balance at end of period	$ 118,184	$ 181,310

Loans and Leases and the Allo45

Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,017,198	$ 988,997
Provision for credit losses	43,000	55,000
Net charge-offs
Charge-offs	(56,752)	(62,564)
Recoveries	16,225	19,997
Net (charge-offs) recoveries	(40,527)	(42,567)
Ending balance	1,019,671	1,001,430
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	328,599	330,833
Provision for credit losses	7,230	28,823
Net charge-offs
Charge-offs	(14,581)	(16,357)
Recoveries	4,823	4,461
Net (charge-offs) recoveries	(9,758)	(11,896)
Ending balance	326,071	347,760
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	374,085	362,719
Provision for credit losses	(5,225)	1,262
Net charge-offs
Charge-offs	(1,366)	(5,445)
Recoveries	223	1,474
Net (charge-offs) recoveries	(1,143)	(3,971)
Ending balance	367,717	360,010
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	65,405	61,127
Provision for credit losses	10,486	5,637
Net charge-offs
Charge-offs	(4,354)	(6,259)
Recoveries	1,510	1,507
Net (charge-offs) recoveries	(2,844)	(4,752)
Ending balance	73,047	62,012
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	170,809	156,288
Provision for credit losses	29,814	18,832
Net charge-offs
Charge-offs	(36,451)	(34,503)
Recoveries	9,669	12,555
Net (charge-offs) recoveries	(26,782)	(21,948)
Ending balance	173,841	153,172
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,300	78,030
Provision for credit losses	695	446
Net charge-offs
Ending balance	$ 78,995	$ 78,476

Loans and Leases and the Allo46

Loans and Leases and the Allowance for Credit Losses - Impaired Loans and Leases (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	$ 512,854	$ 499,152
Unpaid principal balance with related allowance	619,570	585,903
Related allowance	76,409	75,762
Recorded investment with no related allowance	242,407	261,157
Unpaid principal balance with no related allowance	295,400	314,587
Recorded investment	755,261	760,309
Unpaid principal balance	914,970	900,490
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	77,118	67,199
Unpaid principal balance with related allowance	88,313	75,084
Related allowance	9,981	9,140
Recorded investment with no related allowance	96,267	138,356
Unpaid principal balance with no related allowance	104,911	149,716
Recorded investment	173,385	205,555
Unpaid principal balance	193,224	224,800
Automobile [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	12,797	13,498
Unpaid principal balance with related allowance	15,461	15,737
Related allowance	2,694	2,811
Recorded investment	12,797	13,498
Unpaid principal balance	15,461	15,737
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	172,385	177,250
Unpaid principal balance with related allowance	203,464	194,257
Related allowance	45,501	45,488
Recorded investment with no related allowance	115,336	89,126
Unpaid principal balance with no related allowance	145,450	115,327
Recorded investment	287,721	266,376
Unpaid principal balance	348,914	309,584
Residential Builder and Developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	5,536	5,320
Unpaid principal balance with related allowance	5,828	5,641
Related allowance	187	308
Recorded investment with no related allowance	3,760	5,057
Unpaid principal balance with no related allowance	3,832	5,296
Recorded investment	9,296	10,377
Unpaid principal balance	9,660	10,937
Other Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	3,893	4,817
Unpaid principal balance with related allowance	19,598	20,357
Related allowance	456	647
Recorded investment with no related allowance	5,425	5,456
Unpaid principal balance with no related allowance	9,142	9,130
Recorded investment	9,318	10,273
Unpaid principal balance	28,740	29,487
Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	112,068	101,724
Unpaid principal balance with related allowance	134,431	122,602
Related allowance	4,048	4,000
Recorded investment with no related allowance	13,868	13,574
Unpaid principal balance with no related allowance	19,105	18,980
Recorded investment	125,936	115,298
Unpaid principal balance	153,536	141,582
Residential Limited Documentation [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	76,984	77,277
Unpaid principal balance with related allowance	92,586	92,439
Related allowance	4,000	3,900
Recorded investment with no related allowance	7,751	9,588
Unpaid principal balance with no related allowance	12,960	16,138
Recorded investment	84,735	86,865
Unpaid principal balance	105,546	108,577
Home Equity Lines and Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	48,991	48,847
Unpaid principal balance with related allowance	54,032	53,914
Related allowance	8,913	8,812
Recorded investment	48,991	48,847
Unpaid principal balance	54,032	53,914
Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment with related allowance	3,082	3,220
Unpaid principal balance with related allowance	5,857	5,872
Related allowance	629	656
Recorded investment	3,082	3,220
Unpaid principal balance	$ 5,857	$ 5,872

Loans and Leases and the Allo47

Loans and Leases and the Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 745,805	$ 757,701
Interest income recognized, Total	9,971	6,611
Interest income recognized, Cash basis	7,320	4,009
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	181,846	182,857
Interest income recognized, Total	3,147	975
Interest income recognized, Cash basis	3,147	975
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	272,172	271,825
Interest income recognized, Total	783	478
Interest income recognized, Cash basis	783	478
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	9,840	20,051
Interest income recognized, Total	1,682	429
Interest income recognized, Cash basis	1,682	429
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	10,102	16,328
Interest income recognized, Total	6	847
Interest income recognized, Cash basis	6	847
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	121,209	103,875
Interest income recognized, Total	1,902	1,636
Interest income recognized, Cash basis	902	774
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	85,595	97,121
Interest income recognized, Total	1,728	1,500
Interest income recognized, Cash basis	696	384
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	48,797	45,542
Interest income recognized, Total	414	399
Interest income recognized, Cash basis	86	100
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	13,125	16,504
Interest income recognized, Total	224	275
Interest income recognized, Cash basis	15	19
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	3,119	3,598
Interest income recognized, Total	85	72
Interest income recognized, Cash basis	$ 3	$ 3

Loans and Leases and the Allo48

Loans and Leases and the Allowance for Credit Losses - Summary of Loan Grades (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 87,710,749	$ 87,988,983
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,697,522	21,742,651
Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,484,737	20,490,486
Commercial, Financial, Leasing, etc. [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	950,193	1,011,174
Commercial, Financial, Leasing, etc. [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	262,592	240,991
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	25,342,957	25,288,943
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	24,525,402	24,380,184
Commercial [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	664,723	723,777
Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	152,832	184,982
Residential Builder and Developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,648,494	1,631,718
Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,505,502	1,485,148
Residential Builder and Developer [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	138,473	140,119
Residential Builder and Developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	4,519	6,451
Other Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	6,762,055	6,445,712
Other Commercial Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	6,654,458	6,270,812
Other Commercial Construction [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	98,435	164,812
Other Commercial Construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 9,162	$ 10,088

Loans and Leases and the Allo49

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	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	$ 76,409	$ 75,762
Allowance for credit losses	850,361	853,276
Allowance for credit losses	1,019,671	1,017,198	$ 1,001,430	$ 988,997
Purchased Impaired [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	13,906	9,860
Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	940,676	938,898
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	78,995	78,300	$ 78,476	$ 78,030
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	45,501	45,488
Allowance for credit losses	280,570	283,111
Commercial, Financial, Leasing, etc. [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	326,071	328,599
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	10,624	10,095
Allowance for credit losses	357,093	363,990
Commercial Real Estate [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	367,717	374,085
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	8,048	7,900
Allowance for credit losses	51,093	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	13,906	9,860
Residential Real Estate [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	73,047	65,405
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	12,236	12,279
Allowance for credit losses	161,605	158,530
Consumer Loans [Member] | Allocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses	$ 173,841	$ 170,809

Loans and Leases and the Allo50

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	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 87,710,749	$ 87,988,983
Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	755,261	760,309
Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	86,577,488	86,818,659
Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	378,000	410,015
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,697,522	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	287,721	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	21,409,799	21,476,254
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2	21
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	33,753,506	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	191,999	226,205
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	33,548,212	33,117,512
Commercial Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	13,295	22,656
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	18,960,946	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	210,671	202,163
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	18,385,572	19,023,843
Residential Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	364,703	387,338
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	13,298,775	13,266,615
Consumer Loans [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	64,870	65,565
Consumer Loans [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 13,233,905	$ 13,201,050

Loans and Leases and the Allo51

Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)Modification	Mar. 31, 2017USD ($)Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	150	168
Pre-modification recorded investment	$ 70,002	$ 44,692
Post- modification	$ 72,622	$ 39,892
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	20	20
Pre-modification recorded investment	$ 6,780	$ 6,702
Post- modification	6,751	6,597
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	49,656	13,647
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	5,824	2,991
Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	624
Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		1,297
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	22,342	24,948
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 927	$ 3,606
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	56	50
Pre-modification recorded investment	$ 47,994	$ 11,921
Post- modification	49,344	7,923
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	35,673	4,389
Commercial, Financial, Leasing, etc. [Member] | Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	624
Commercial, Financial, Leasing, etc. [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		806
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 13,047	$ 2,728
Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	1	1
Pre-modification recorded investment	$ 752	$ 102
Post- modification	746	102
Other Commercial Construction [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 746	$ 102
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	47	41
Pre-modification recorded investment	$ 12,636	$ 9,380
Post- modification	13,847	9,948
Residential [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	6,945	5,593
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 6,902	$ 4,355
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	2	6
Pre-modification recorded investment	$ 295	$ 1,378
Post- modification	385	1,525
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	267
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 118	$ 1,525
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	14	25
Pre-modification recorded investment	$ 1,348	$ 2,502
Post- modification	1,352	2,502
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	4	163
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	$ 1,348	$ 1,848
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
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	8	20
Pre-modification recorded investment	$ 148	$ 390
Post- modification	148	390
Automobile [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 148	383
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 7
Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	2	2
Pre-modification recorded investment	$ 49	$ 26
Post- modification	49	26
Other [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 49	$ 26

Borrowings - Additional Informa

Borrowings - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Junior subordinated debentures		$ 520
Debt Maturity, Start Year		Jan. 1, 2027
Debt Maturity, End Year		Dec. 31, 2033
Agreements to repurchase securities		$ 419	$ 422
Collateral posted		$ 436	$ 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%
London Interbank Offered Rate (LIBOR) [Member] | Bank Note Program Variable Interest Rate [Member]
Debt Instrument [Line Items]
Senior notes	$ 350

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Detail) - $ / shares	3 Months Ended
	Mar. 31, 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	$ 518.18
Warrant to purchase common stock	95,525
Warrants, date of expiration	Dec. 12, 2018

Shareholders' Equity - Issued a

Shareholders' Equity - Issued and Outstanding Preferred Stock (Detail) - USD ($) $ in Thousands	Mar. 31, 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 - Issued55

Shareholders' Equity - Issued and Outstanding Preferred Stock (Parenthetical) (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 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	$ 73.75
Warrants and rights outstanding	220,034
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 Postr56

Pension Plans and Other Postretirement Benefits - Net Periodic Defined Benefit Cost for Defined Benefit Plans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,103	$ 4,908
Interest cost on projected benefit obligation	18,805	19,691
Expected return on plan assets	(30,875)	(27,200)
Amortization of prior service cost (credit)	125	125
Amortization of net actuarial loss	11,100	6,800
Net periodic benefit cost	4,258	4,324
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	226	383
Interest cost on projected benefit obligation	557	1,080
Amortization of prior service cost (credit)	(1,175)	(350)
Amortization of net actuarial loss	(200)	(25)
Net periodic benefit cost	$ (592)	$ 1,088

Pension Plans and Other Postr57

Pension Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Defined contribution pension and retirement savings plans total expense	$ 21,274,000	$ 19,419,000

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
	Mar. 31, 2018	Mar. 31, 2017
Income available to common shareholders:
Net income	$ 352,610	$ 348,927
Less: Preferred stock dividends	(18,130)	(18,237)
Net income available to common equity	334,480	330,690
Less: Income attributable to unvested stock-based compensation awards	(1,732)	(2,128)
Net income available to common shareholders	$ 332,748	$ 328,562
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	149,470	155,463
Less: Unvested stock-based compensation awards	(782)	(1,036)
Weighted-average shares outstanding	148,688	154,427
Basic earnings per common share	$ 2.24	$ 2.13

Earnings Per Common Share - C59

Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income available to common equity	$ 334,480	$ 330,690
Less: Income attributable to unvested stock-based compensation awards	(1,731)	(2,123)
Net income available to common shareholders	$ 332,749	$ 328,567
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	149,470	155,463
Less: Unvested stock-based compensation awards	(782)	(1,036)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	217	522
Adjusted weighted-average shares outstanding	148,905	154,949
Diluted earnings per common share	$ 2.23	$ 2.12

Earnings Per Common Share - Add

Earnings Per Common Share - Additional Information (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	237,584	391,764

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
	Mar. 31, 2018	Mar. 31, 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	(145,457)	(3,015)
Foreign currency translation adjustment, before tax	1,632	732
Unrealized losses on cash flow hedges, before tax	(14,719)
Total other comprehensive income (loss) before reclassifications, before tax	(158,544)	(2,283)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax	810	787
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(28)	(39)
Net yield adjustment from cash flow hedges currently in effect, before tax	580
Amortization of prior service credit, before tax	(1,050)	(225)
Amortization of actuarial losses, before tax	10,900	6,775
Total other comprehensive income (loss), before tax	(147,332)	5,015
Ending balance, before tax	(663,417)	(480,230)
Beginning balance, tax	129,476	190,609
Cumulative effect of change in accounting principles — equity securities, tax	5,942
Unrealized holding gains (losses), tax	44,176	1,182
Foreign currency translation adjustment, tax	(342)	(256)
Unrealized losses on cash flow hedges, tax	3,870
Total other comprehensive income (loss) before reclassifications, tax	47,704	926
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, tax	(213)	(310)
Accretion of net gain (losses) on terminated cash flow hedges, tax	7	16
Net yield adjustment from cash flow hedges currently in effect, tax	(152)
Amortization of prior service credit, tax	276	88
Amortization of actuarial losses, tax	(2,866)	(2,666)
Total other comprehensive income (loss), tax	44,756	(1,946)
Ending balance, tax	180,174	188,663
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	(101,281)	(1,833)
Foreign currency translation adjustment, net of tax	1,290	476
Unrealized losses on cash flow hedges, net of tax	(10,849)
Total other comprehensive income (loss) before reclassifications, net of tax	(110,840)	(1,357)
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, net of tax	597	477
Accretion of net gain on terminated cash flow hedges, net of tax	(21)	(23)
Net yield adjustment from cash flow hedges currently in effect, net of tax	428
Amortization of prior service credit, net of tax	(774)	(137)
Amortization of actuarial losses, net of tax	8,034	4,109
Total other comprehensive income (loss)	(102,576)	3,069
Ending balance, net of tax	(483,243)	(291,567)
Total other comprehensive income(loss), before tax	(147,332)	5,015
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	(145,457)
Total other comprehensive income (loss) before reclassifications, before tax	(145,457)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax	810
Total other comprehensive income (loss), before tax	(144,647)
Ending balance, before tax	(227,399)
Cumulative effect of change in accounting principles- equity securities	(16,853)
Total other comprehensive income (loss)	(100,684)
Total other comprehensive income(loss), before tax	(144,647)
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	(1,050)	(225)
Amortization of actuarial losses, before tax	10,900	6,775
Total other comprehensive income (loss), before tax	9,850	6,550
Ending balance, before tax	(403,318)	(443,367)
Total other comprehensive income (loss)	7,260
Total other comprehensive income(loss), before tax	9,850	6,550
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(20,165)	(8,268)
Foreign currency translation adjustment, before tax	1,632	732
Unrealized losses on cash flow hedges, before tax	(14,719)
Total other comprehensive income (loss) before reclassifications, before tax	(13,087)	732
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(28)	(39)
Net yield adjustment from cash flow hedges currently in effect, before tax	580
Total other comprehensive income (loss), before tax	(12,535)	693
Ending balance, before tax	(32,700)	(7,575)
Total other comprehensive income(loss), before tax	$ (12,535)	693
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax		46,725
Unrealized holding gains (losses), before tax		(8,628)
Total other comprehensive income (loss) before reclassifications, before tax		(8,628)
Total other comprehensive income (loss), before tax		(8,628)
Ending balance, before tax		38,097
Total other comprehensive income(loss), before tax		(8,628)
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax		(73,785)
Unrealized holding gains (losses), before tax		5,613
Total other comprehensive income (loss) before reclassifications, before tax		5,613
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax		787
Total other comprehensive income (loss), before tax		6,400
Ending balance, before tax		(67,385)
Total other comprehensive income(loss), before tax		$ 6,400

Comprehensive Income - Accumula

Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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	(102,576)	3,069
Ending balance	15,709,694	16,213,104
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	(100,684)
Ending balance	(161,687)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(304,546)
Net gain (loss) during period	7,260
Ending balance	(297,286)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(15,118)
Net gain (loss) during period	(9,152)
Ending balance	(24,270)
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	(102,576)
Ending balance	$ (483,243)	$ (291,567)

Derivative Financial Instrume63

Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes	$ 9,550,000,000		$ 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	17,000,000		16,000,000
Aggregate fair value of derivative financial instruments in a liability position	4,000,000		13,000,000
Net liability positions with counterparties	4,000,000		13,000,000
Aggregate fair value of derivative financial instruments in asset position	38,000,000		13,000,000
Net fair value of derivative financial instruments in a net asset position	38,000,000		13,000,000
Collateral relating to net asset positions	32,000,000		12,000,000
Counterparties [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	4,000,000		12,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Amount of initial margin posted	53,000,000		52,000,000
Reduction in the fair value of derivative asset due to contractual settlements	(122,000,000)
Reduction in the fair value of derivative liability due to contractual settlements	(6,000,000)
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	1,000,000	$ 4,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading account purposes		39,500,000,000	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		$ 538,000,000	$ 530,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Fair value of additional collateral to be posted for derivative financial instruments	$ 0

Derivative Financial Instrume64

Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Amount	$ 9,550,000,000	$ 9,400,000,000
Average Maturity (in years)	2 years 6 months	2 years 6 months
Estimated Fair Value Gain	$ 376,000	$ 639,000
Interest Payments On Variable Rate Commercial Real Estate Loans [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Notional Amount	$ 4,850,000,000	$ 4,850,000,000
Average Maturity (in years)	1 year 8 months 12 days	2 years
Weighted-Average Rate, Fixed	1.52%	1.52%
Weighted-Average Rate, Variable	1.66%	1.36%
Estimated Fair Value Gain	$ 60,000	$ 66,000
Fixed Rate Long-Term Borrowings [Member] | Fair Value Hedges [Member]
Derivative [Line Items]
Notional Amount	$ 4,700,000,000	$ 4,550,000,000
Average Maturity (in years)	3 years	2 years 10 months 25 days
Weighted-Average Rate, Fixed	2.41%	2.27%
Weighted-Average Rate, Variable	2.48%	2.09%
Estimated Fair Value Gain	$ 316,000	$ 573,000

Derivative Financial Instrume65

Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Parenthetical) (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Amount	$ 9,550,000,000	$ 9,400,000,000
Forward-Starting Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Notional Amount	2,000,000,000
Fair Value Hedges [Member]
Derivative [Line Items]
Reduction of estimated fair value losses on hedging instruments	83,200,000	41,100,000
Cash Flow Hedges [Member]
Derivative [Line Items]
Reduction of estimated fair value losses on hedging instruments	$ 30,400,000	$ 16,300,000

Derivative Financial Instrume66

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 96,198	$ 92,517
Liability Derivatives, Fair Value	242,447	139,186
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	94,487	91,144
Liability Derivatives, Fair Value	240,977	138,903
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	1,711	1,373
Liability Derivatives, Fair Value	1,470	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	376	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	5,361	2,526
Liability Derivatives, Fair Value	2,341	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	1,335	734
Liability Derivatives, Fair Value	1,470	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	10,562	8,797
Liability Derivatives, Fair Value	1,802	494
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	71,930	74,164
Liability Derivatives, Fair Value	231,254	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	6,634	5,657
Liability Derivatives, Fair Value	$ 5,580	$ 5,286

Derivative Financial Instrume67

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Offsetting [Abstract]
Reduction in estimated fair value of interest rate contracts in asset position	$ 235.6	$ 136.2
Reduction in estimated fair value of interest rate contracts in liability position	$ 6.2	$ 12.2

Derivative Financial Instrume68

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Statement of Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 1,026	$ 3,786
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	(42,390)	(4,119)
Derivatives in fair value hedging relationships, Hedged item	42,370	4,012
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	(1,605)	1,950
Foreign Exchange and Other Option and Futures Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 2,631	$ 1,836

Derivative Financial Instrume69

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	Mar. 31, 2018	Dec. 31, 2017
Carrying Amount [Member]
Derivatives, Fair Value [Line Items]
Hedged Item	$ 4,612,063	$ 4,504,029
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Derivatives, Fair Value [Line Items]
Hedged Item	$ (82,503)	$ (40,133)

Variable Interest Entities an70

Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Variable Interest Entity Disclosure [Abstract]
Other assets for its "investment" in the common securities recognized by the company of various trusts	$ 23,000,000		$ 23,000,000
Total assets of partnerships in which the company invested	1,000,000,000		1,000,000,000
Maximum exposure to loss of investments in real estate partnerships	422,000,000		420,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	196,000,000		$ 201,000,000
Investments amortized to income tax expense	13,000,000	$ 13,000,000
Federal tax credits and other federal tax benefits recognized	$ 16,000,000	$ 16,000,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account assets	$ 141,134	$ 132,909
Investment securities	10,297,856	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	1,941,478	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	2,000	2,589
Government Issued or Guaranteed [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	8,222,129	8,716,392
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	132,222	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	141,134	132,909
Investment securities	10,297,856	10,896,284
Real estate loans held for sale	455,196	378,047
Other assets	17,634	12,696
Total assets	10,973,537	11,419,936
Trading account liabilities	236,834	137,390
Other liabilities	5,613	1,796
Total liabilities	242,447	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	46,215	47,873
Investment securities		73,232
Total assets	89,711	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	94,919	85,036
Investment securities	10,297,829	10,823,024
Real estate loans held for sale	455,196	378,047
Other assets	7,072	3,899
Total assets	10,873,237	11,290,006
Trading account liabilities	236,834	137,390
Other liabilities	3,811	1,302
Total liabilities	240,645	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	27	28
Other assets	10,562	8,797
Total assets	10,589	8,825
Other liabilities	1,802	494
Total liabilities	1,802	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	1,941,478	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	1,941,478	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	2,000	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	2,000	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	8,222,129	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	8,222,129	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	27	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	27	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	132,222	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	132,222	128,832
Fair Value Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	61,717	100,956
Fair Value Measurements, Recurring [Member] | Equity Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	43,496	73,232
Fair Value Measurements, Recurring [Member] | Equity Securities [Member] | Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities	$ 18,221	$ 27,724

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
	Mar. 31, 2018	Mar. 31, 2017
Privately Issued [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 28	$ 44
Total gains (losses) realized/unrealized:
Settlements	(1)	(3)
Ending Balance	27	41
Other Assets and Other Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	8,303	7,325
Total gains (losses) realized/unrealized:
Included in earnings	8,130	23,940
Transfers in and/or out of Level 3	(7,673)	(15,063)
Ending Balance	8,760	16,202
Changes in unrealized gains included in earnings related to assets still held at end of period	$ 8,778	$ 15,094

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
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	$ 27	$ 42
Fair Value, Measurements, Nonrecurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	178	210	$ 210
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	19	32
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	97	88	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	$ 81	$ 122	$ 65

Fair Value Measurements - Quant

Fair Value Measurements - Quantitative Information Related to Significant Unobservable Inputs (Detail) - Fair Value Measurements, Recurring [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Privately Issued [Member] | Two Independent Pricing Quotes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Recurring fair value measurements for certain Level 3 Assets and Liabilities	$ 27	$ 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	$ 8,760	$ 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	76.00%	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	19.00%	22.00%

Fair Value Measurements - Carry

Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financial assets:
Interest-bearing deposits at banks	$ 6,135,434	$ 5,078,903
Trading account assets	141,134	132,909
Investment securities	14,066,564	14,664,525
Loans and leases:
Allowance for credit losses	(1,019,671)	(1,017,198)	$ (1,001,430)	$ (988,997)
Loans and leases, net	86,691,078	86,971,785
Financial liabilities:
Noninterest-bearing deposits	(31,817,516)	(33,975,180)
Savings and interest-checking deposits	(52,724,608)	(51,698,008)
Time deposits	(6,126,442)	(6,580,962)
Deposits at Cayman Islands office	(278,064)	(177,996)
Long-term borrowings	(8,591,051)	(8,141,430)
Estimate Fair Value [Member]
Financial assets:
Cash and cash equivalents	1,292,664	1,420,888
Interest-bearing deposits at banks	6,135,434	5,078,903
Trading account assets	141,134	132,909
Investment securities	13,998,023	14,653,074
Loans and leases:
Commercial loans and leases	21,294,038	21,321,282
Commercial real estate loans	33,123,306	32,950,724
Residential real estate loans	18,812,289	19,596,826
Consumer loans	13,112,874	13,161,517
Loans and leases, net	86,342,507	87,030,349
Accrued interest receivable	332,151	327,170
Financial liabilities:
Noninterest-bearing deposits	(31,817,516)	(33,975,180)
Savings and interest-checking deposits	(52,724,608)	(51,698,008)
Time deposits	(6,177,695)	(6,635,048)
Deposits at Cayman Islands office	(278,064)	(177,996)
Short-term borrowings	(1,626,129)	(175,099)
Long-term borrowings	(8,598,328)	(8,193,783)
Accrued interest payable	(65,819)	(75,641)
Trading account liabilities	(236,834)	(137,390)
Other financial instruments:
Commitments to originate real estate loans for sale	8,760	8,303
Commitments to sell real estate loans	2,885	1,958
Other credit-related commitments	(122,805)	(125,281)
Interest rate swap agreements used for interest rate risk management	376	639
Estimate Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,206,172	1,352,035
Trading account assets	46,215	47,873
Investment securities	43,496	73,232
Estimate Fair Value [Member] | Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	86,492	68,853
Interest-bearing deposits at banks	6,135,434	5,078,903
Trading account assets	94,919	85,036
Investment securities	13,841,655	14,469,127
Loans and leases:
Commercial real estate loans	166,773	22,130
Residential real estate loans	4,226,284	4,440,645
Loans and leases, net	4,393,057	4,462,775
Accrued interest receivable	332,151	327,170
Financial liabilities:
Noninterest-bearing deposits	(31,817,516)	(33,975,180)
Savings and interest-checking deposits	(52,724,608)	(51,698,008)
Time deposits	(6,177,695)	(6,635,048)
Deposits at Cayman Islands office	(278,064)	(177,996)
Short-term borrowings	(1,626,129)	(175,099)
Long-term borrowings	(8,598,328)	(8,193,783)
Accrued interest payable	(65,819)	(75,641)
Trading account liabilities	(236,834)	(137,390)
Other financial instruments:
Commitments to sell real estate loans	2,885	1,958
Interest rate swap agreements used for interest rate risk management	376	639
Estimate Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Investment securities	112,872	110,715
Loans and leases:
Commercial loans and leases	21,294,038	21,321,282
Commercial real estate loans	32,956,533	32,928,594
Residential real estate loans	14,586,005	15,156,181
Consumer loans	13,112,874	13,161,517
Loans and leases, net	81,949,450	82,567,574
Other financial instruments:
Commitments to originate real estate loans for sale	8,760	8,303
Other credit-related commitments	(122,805)	(125,281)
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,292,664	1,420,888
Interest-bearing deposits at banks	6,135,434	5,078,903
Trading account assets	141,134	132,909
Investment securities	14,066,564	14,664,525
Loans and leases:
Commercial loans and leases	21,697,522	21,742,651
Commercial real estate loans	33,753,506	33,366,373
Residential real estate loans	18,960,946	19,613,344
Consumer loans	13,298,775	13,266,615
Allowance for credit losses	(1,019,671)	(1,017,198)
Loans and leases, net	86,691,078	86,971,785
Accrued interest receivable	332,151	327,170
Financial liabilities:
Noninterest-bearing deposits	(31,817,516)	(33,975,180)
Savings and interest-checking deposits	(52,724,608)	(51,698,008)
Time deposits	(6,126,442)	(6,580,962)
Deposits at Cayman Islands office	(278,064)	(177,996)
Short-term borrowings	(1,626,129)	(175,099)
Long-term borrowings	(8,591,051)	(8,141,430)
Accrued interest payable	(65,819)	(75,641)
Trading account liabilities	(236,834)	(137,390)
Other financial instruments:
Commitments to originate real estate loans for sale	8,760	8,303
Commitments to sell real estate loans	2,885	1,958
Other credit-related commitments	(122,805)	(125,281)
Interest rate swap agreements used for interest rate risk management	$ 376	$ 639

Commitments and Contingencies -

Commitments and Contingencies - Company's Significant Commitments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Commitments to extend credit
Home equity lines of credit	$ 5,518,820	$ 5,482,622
Commercial real estate loans to be sold	288,883	194,763
Other commercial real estate	5,788,080	6,050,569
Residential real estate loans to be sold	343,400	347,113
Other residential real estate	223,589	201,426
Commercial and other	12,951,589	12,733,815
Standby letters of credit	2,477,474	2,497,844
Commercial letters of credit	56,245	46,739
Financial guarantees and indemnification contracts	3,449,447	3,434,381
Commitments to sell real estate loans	$ 977,257	$ 812,217

Commitments and Contingencies77

Commitments and Contingencies - Additional Information (Detail) - USD ($)	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
Litigation reserve	135,000,000
Minimum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses	0
Maximum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses	$ 50,000,000

Segment Information - Summary o

Segment Information - Summary of Reclassified Segment Information on Comparable Basis (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net income	$ 352,610	$ 348,927
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,434,213	1,361,105
As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		348,927
As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		1,361,105
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income	37,718	24,988
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	127,884	120,333
Business Banking [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		22,407
Business Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		115,981
Business Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		2,581
Business Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		4,352
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income	125,465	112,787
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	266,396	273,908
Commercial Banking [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		112,750
Commercial Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		273,845
Commercial Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		37
Commercial Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		63
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income	108,303	84,547
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	202,607	195,125
Commercial Real Estate [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		84,547
Commercial Real Estate [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		195,125
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income	19,739	33,945
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	50,038	78,946
Discretionary Portfolio [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		33,945
Discretionary Portfolio [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		78,946
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income	14,946	9,917
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	82,458	85,401
Residential Mortgage Banking [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		14,844
Residential Mortgage Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		93,708
Residential Mortgage Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		(4,927)
Residential Mortgage Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		(8,307)
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income	123,380	86,191
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	393,476	368,518
Retail Banking [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		81,873
Retail Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		361,237
Retail Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		4,318
Retail Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		7,281
All Other [Member]
Segment Reporting Information [Line Items]
Net income	(76,941)	(3,448)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ 311,354	238,874
All Other [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		(1,439)
All Other [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		242,263
All Other [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		(2,009)
All Other [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		$ (3,389)

Segment Information - Informati

Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 352,610	$ 348,927
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,434,213	1,361,105
Business Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	37,718	24,988
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	127,884	120,333
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	918	911
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	125,465	112,787
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	266,396	273,908
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	850	920
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	108,303	84,547
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	202,607	195,125
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	340	407
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	19,739	33,945
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	50,038	78,946
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(10,832)	(12,927)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	14,946	9,917
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	82,458	85,401
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	15,421	18,211
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	123,380	86,191
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	393,476	368,518
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	2,865	3,047
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	(76,941)	(3,448)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	311,354	238,874
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (9,562)	$ (10,569)

Segment Information - Summary80

Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Segment Reporting Information [Line Items]
Average Total Assets	$ 117,684	$ 120,860	$ 122,978
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	5,681	5,602	5,596
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	26,482	26,573	26,723
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Total Assets	22,811	22,741	22,977
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Total Assets	34,095	37,203	38,731
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	2,278	2,355	2,426
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	13,377	12,702	12,204
All Other [Member]
Segment Reporting Information [Line Items]
Average Total Assets	$ 12,960	$ 13,684	$ 14,321

Segment Information - Summary81

Segment Information - Summary of Segment Information (Parenthetical) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting [Abstract]
Taxable-equivalent adjustment	$ 4,809,000	$ 7,999,000

Relationship with Bayview Len82

Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 8,591,051		$ 8,141,430
Bayview Lending Group [Member]
Schedule of Equity Method Investments [Line Items]
Minority interest in Bayview Lending Group LLC	20.00%
Carrying value of minority interest investment in Bayview Lending Group LLC	$ 0
Bayview Lending Group [Member] | Other Revenues From Operations [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	23,000	$ (2,000)
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	2,900,000		3,000,000
Revenues from servicing	4,000	4,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	55,800,000		56,600,000
Revenues from sub-servicing	30,000	$ 23,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	129,000		$ 136,000
Bayview Financial [Member] | Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	750,000
Bayview Financial [Member] | Syndicated Loan Facility [Member] | M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 90,000

Revenue from Contracts with C83

Revenue from Contracts with Customers - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Uncollected amounts receivable	$ 49
Accrued interest and other liabilities [Member]
Disaggregation Of Revenue [Line Items]
Deferred revenue	$ 43
Maximum [Member]
Disaggregation Of Revenue [Line Items]
Period of satisfaction of contract with customer	1 year
ASU 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Expense recognized on credit card rewards in other costs of operations	$ 3	$ 2

Revenue from Contracts with C84

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
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	$ 105,115	$ 104,176
Trust income	131,375	120,015
Brokerage services income	13,392	17,384
Other revenues from operations:
Total other income	458,696	$ 446,845
ASU 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	105,115
Trust income	131,375
Brokerage services income	13,392
Other revenues from operations:
Merchant discount and credit card fees	24,772
Other	22,890
Total other income	297,544
ASU 2014-09 [Member] | Business Banking [Member]
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	15,404
Other revenues from operations:
Merchant discount and credit card fees	7,503
Total other income	22,907
ASU 2014-09 [Member] | Commercial Banking [Member]
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	24,654
Other revenues from operations:
Merchant discount and credit card fees	12,712
Other	1,563
Total other income	38,929
ASU 2014-09 [Member] | Commercial Real Estate [Member]
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	2,764
Other revenues from operations:
Merchant discount and credit card fees	554
Other	859
Total other income	4,177
ASU 2014-09 [Member] | Discretionary Portfolio [Member]
Other revenues from operations:
Other	452
Total other income	452
ASU 2014-09 [Member] | Residential Mortgage Banking [Member]
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	3
Other revenues from operations:
Other	1,043
Total other income	1,046
ASU 2014-09 [Member] | Retail Banking [Member]
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	60,601
Other revenues from operations:
Merchant discount and credit card fees	3,388
Other	9,865
Total other income	73,854
ASU 2014-09 [Member] | All Other [Member]
Disaggregation Of Revenue [Line Items]
Service charges on deposit accounts	1,689
Trust income	131,375
Brokerage services income	13,392
Other revenues from operations:
Merchant discount and credit card fees	615
Other	9,108
Total other income	$ 156,179

Recent Accounting Developments

Recent Accounting Developments - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 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
Gain (loss) on bank investment securities	(9,431)
ASU 2016-01 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Gain (loss) on bank investment securities	$ 9,000
ASU 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Minimum lease payments under non cancelable operating lease		$ 429,000
Lessee, operating lease term	12 months