M&T Bank (MTB) 10-K 20 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 13, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	MTB
Entity Registrant Name	M&T BANK CORP
Entity Central Index Key	36270
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		132,912,535
Entity Public Float			$14,427,352,292

Consolidated_Balance_Sheet

Consolidated Balance Sheet (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets
Cash and due from banks	$1,289,965	$1,573,361
Interest-bearing deposits at banks	6,470,867	1,651,138
Federal funds sold	83,392	99,573
Trading account	308,175	376,131
Investment securities (includes pledged securities that can be sold or repledged of $1,631,267 at December 31, 2014; $1,696,438 at December 31, 2013)
Available for sale (cost: $8,919,324 at December 31, 2014; $4,444,365 at December 31, 2013)	9,156,932	4,531,786
Held to maturity (fair value: $3,538,282 at December 31, 2014; $3,860,127 at December 31, 2013)	3,507,868	3,966,130
Other (fair value: $328,742 at December 31, 2014; $298,581 at December 31, 2013)	328,742	298,581
Total investment securities	12,993,542	8,796,497
Loans and leases	66,899,369	64,325,783
Unearned discount	-230,413	-252,624
Loans and leases, net of unearned discount	66,668,956	64,073,159
Allowance for credit losses	-919,562	-916,676
Loans and leases, net	65,749,394	63,156,483
Premises and equipment	612,984	633,520
Goodwill	3,524,625	3,524,625
Core deposit and other intangible assets	35,027	68,851
Accrued interest and other assets	5,617,564	5,282,212
Total assets	96,685,535	85,162,391
Liabilities
Noninterest-bearing deposits	26,947,880	24,661,007
NOW accounts	2,307,815	1,989,441
Savings deposits	41,085,803	36,621,580
Time deposits	3,063,973	3,523,838
Deposits at Cayman Islands office	176,582	322,746
Total deposits	73,582,053	67,118,612
Federal funds purchased and agreements to repurchase securities	192,676	260,455
Accrued interest and other liabilities	1,567,951	1,368,922
Long-term borrowings	9,006,959	5,108,870
Total liabilities	84,349,639	73,856,859
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 December 31, 2014; 381,500 shares at December 31, 2013; Liquidation preference of $10,000 per share: 50,000 shares at December 31, 2014 and December 31, 2013	1,231,500	881,500
Common stock, $.50 par, 250,000,000 shares authorized, 132,312,931 shares issued at December 31, 2014; 130,516,364 shares issued at December 31, 2013	66,157	65,258
Common stock issuable, 41,330 shares at December 31, 2014; 47,231 shares at December 31, 2013	2,608	2,915
Additional paid-in capital	3,409,506	3,232,014
Retained earnings	7,807,119	7,188,004
Accumulated other comprehensive income (loss), net	-180,994	-64,159
Total shareholders' equity	12,335,896	11,305,532
Total liabilities and shareholders' equity	$96,685,535	$85,162,391

Consolidated_Balance_Sheet_Par

Consolidated Balance Sheet (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Pledged securities that can be sold or repledged	$1,631,267	$1,696,438
Investment securities, available for sale, amortized cost	8,919,324	4,444,365
Investment securities, held to maturity, fair value	3,538,282	3,860,127
Other, fair value	$328,742	$298,581
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	132,312,931	130,516,364
Common stock issuable, shares	41,330	47,231
Series A and Series C [Member]
Preferred stock, shares issued	731,500	381,500
Preferred stock, shares outstanding	731,500	381,500
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_Inco

Consolidated Statement of Income (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest income
Loans and leases, including fees	$2,596,586	$2,734,708	$2,704,156
Deposits at banks	13,361	5,201	1,221
Federal funds sold	64	104	21
Agreements to resell securities		10
Trading account	1,119	1,265	1,126
Investment securities
Fully taxable	340,391	209,244	227,116
Exempt from federal taxes	5,356	6,802	8,045
Total interest income	2,956,877	2,957,334	2,941,685
Interest expense
NOW accounts	1,404	1,287	1,343
Savings deposits	45,465	54,948	68,011
Time deposits	15,515	26,439	46,102
Deposits at Cayman Islands office	699	1,018	1,130
Short-term borrowings	101	430	1,286
Long-term borrowings	217,247	199,983	225,297
Total interest expense	280,431	284,105	343,169
Net interest income	2,676,446	2,673,229	2,598,516
Provision for credit losses	124,000	185,000	204,000
Net interest income after provision for credit losses	2,552,446	2,488,229	2,394,516
Other income
Mortgage banking revenues	362,912	331,265	349,064
Service charges on deposit accounts	427,956	446,941	446,698
Trust income	508,258	496,008	471,852
Brokerage services income	67,212	65,647	59,059
Trading account and foreign exchange gains	29,874	40,828	35,634
Gain on bank investment securities		56,457	9
Total other-than-temporary impairment ("OTTI") losses		-1,884	-32,067
Portion of OTTI losses recognized in other comprehensive income (before taxes)		-7,916	-15,755
Net OTTI losses recognized in earnings		-9,800	-47,822
Equity in earnings of Bayview Lending Group LLC	-16,672	-16,126	-21,511
Other revenues from operations	399,733	453,985	374,287
Total other income	1,779,273	1,865,205	1,667,270
Other expense
Salaries and employee benefits	1,404,950	1,355,178	1,314,540
Equipment and net occupancy	269,299	264,327	257,551
Printing, postage and supplies	38,201	39,557	41,929
Amortization of core deposit and other intangible assets	33,824	46,912	60,631
FDIC assessments	55,531	69,584	101,110
Other costs of operations	941,052	860,327	733,499
Total other expense	2,742,857	2,635,885	2,509,260
Income (loss) before taxes	1,588,862	1,717,549	1,552,526
Income taxes	522,616	579,069	523,028
Net income	1,066,246	1,138,480	1,029,498
Net income available to common shareholders
Basic	978,531	1,062,429	953,390
Diluted	$978,581	$1,062,496	$953,429
Net income per common share
Basic	$7.47	$8.26	$7.57
Diluted	$7.42	$8.20	$7.54

Consolidated_Statement_of_Comp

Consolidated Statement of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Partners' Capital [Abstract]
Net income	$1,066,246	$1,138,480	$1,029,498
Other comprehensive income (loss), net of tax and reclassification adjustments:
Net unrealized gains (losses) on investment securities	93,275	-2,865	114,825
Cash flow hedges adjustments	-96		-112
Foreign currency translation adjustment	-2,607	381	519
Defined benefit plans liability adjustments	-207,407	178,589	945
Total other comprehensive income (loss)	-116,835	176,105	116,177
Total comprehensive income	$949,411	$1,314,585	$1,145,675

Consolidated_Statement_of_Cash

Consolidated Statement of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities
Net income	$1,066,246	$1,138,480	$1,029,498
Adjustments to reconcile net income to net cash provided by operating activities
Provision for credit losses	124,000	185,000	204,000
Depreciation and amortization of premises and equipment	96,496	91,469	84,375
Amortization of capitalized servicing rights	68,410	65,354	59,555
Amortization of core deposit and other intangible assets	33,824	46,912	60,631
Provision for deferred income taxes	92,848	139,785	131,858
Asset write-downs	6,593	17,918	63,790
Net gain on sales of assets	-6,859	-127,890	-6,868
Net change in accrued interest receivable, payable	15,163	-10,523	-13,898
Net change in other accrued income and expense	-68,722	71,523	-200,704
Net change in loans originated for sale	-350,581	-674,062	-924,839
Net change in trading account assets and liabilities	21,623	-11,642	12,583
Net cash provided by operating activities	1,099,041	932,324	499,981
Cash flows from investing activities
Proceeds from sales of investment securities Available for sale	16	1,081,802	49,528
Proceeds from sales of investment securities Other	23,445	13,172	78,071
Proceeds from maturities of investment securities Available for sale	998,413	1,034,564	1,585,260
Proceeds from maturities of investment securities Held to maturity	468,999	287,837	329,279
Purchases of investment securities Available for sale	-5,347,145	-197,931	-28,161
Purchases of investment securities Held to maturity	-21,283	-1,977,064	-285,125
Purchases of investment securities Other	-53,606	-9,105	-13,833
Net (increase) decrease in loans and leases	-2,421,162	123,120	-5,672,747
Net (increase) decrease in interest-bearing deposits at banks	-4,819,729	-1,521,193	25,015
Capital expenditures, net	-73,161	-129,563	-91,519
Net increase in loan servicing advances	-484,689	-1,004,923	-69,084
Other, net	19,531	95,706	32,458
Net cash provided (used) by investing activities	-11,710,371	-2,203,578	-4,060,858
Cash flows from financing activities
Net increase in deposits	6,466,697	1,513,884	6,230,391
Net increase (decrease) in short-term borrowings	-67,779	-814,027	292,422
Proceeds from long-term borrowings	4,345,478	799,760
Payments on long-term borrowings	-426,275	-261,212	-2,080,167
Dividends paid - common	-371,199	-365,349	-357,717
Dividends paid - preferred	-70,234	-53,450	-53,450
Proceeds from issuance of preferred stock	346,500
Other, net	88,565	137,967	63,616
Net cash provided by financing activities	10,311,753	957,573	4,095,095
Net increase (decrease) in cash and cash equivalents	-299,577	-313,681	534,218
Cash and cash equivalents at beginning of year	1,672,934	1,986,615	1,452,397
Cash and cash equivalents at end of year	1,373,357	1,672,934	1,986,615
Supplemental disclosure of cash flow information
Interest received during the year	2,893,153	2,894,699	2,931,409
Interest paid during the year	257,553	301,734	371,887
Income taxes paid during the year	411,912	389,008	405,598
Supplemental schedule of noncash investing and financing activities
Securitization of residential mortgage loans allocated to Available-for-sale investment securities	134,698	1,690,490
Securitization of residential mortgage loans allocated to Held to maturity investment securities		1,245,444
Securitization of residential mortgage loans allocated to capitalized servicing rights	1,760	30,879
Real estate acquired in settlement of loans	$43,821	$44,804	$48,932

Consolidated_Statement_of_Chan

Consolidated Statement of Changes in Shareholders' Equity (USD $)	Total	Series E Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]
In Thousands, unless otherwise specified				Series E Preferred Stock [Member]		Series C Stock Warrants [Member]	Series A Warrants [Member]			Series C Stock Warrants [Member]	Series A Warrants [Member]	Series E Preferred Stock [Member]
Beginning Balance at Dec. 31, 2011	$9,271,209		$864,585		$62,842			$4,072	$2,828,986				$5,867,165	($356,441)
Total comprehensive income	1,145,675												1,029,498	116,177
Preferred stock cash dividends	-53,450												-53,450
Amortization of preferred stock discount			7,915										-7,915
Stock-based compensation plans:
Compensation expense, net	48,166				229				47,937
Exercises of stock options, net	135,945				928				135,017
Stock purchase plan	10,117				75				10,042
Directors' stock plan	1,480				9				1,471
Deferred compensation plans, net, including dividend equivalents	-161				5			-599	593				-160
Other	1,474								1,474
Common stock cash dividends - $2.80 per share	-357,862												-357,862
Ending Balance at Dec. 31, 2012	10,202,593		872,500		64,088			3,473	3,025,520				6,477,276	-240,264
Total comprehensive income	1,314,585												1,138,480	176,105
Preferred stock cash dividends	-53,450												-53,450
Amortization of preferred stock discount			9,000										-9,000
Exercise of stock warrants into common stock						93	13			-93	-13
Stock-based compensation plans:
Compensation expense, net	38,027				137				37,890
Exercises of stock options, net	164,805				914				163,891
Directors' stock plan	1,644				8				1,636
Deferred compensation plans, net, including dividend equivalents	-109				5			-558	575				-131
Other	2,608								2,608
Common stock cash dividends - $2.80 per share	-365,171												-365,171
Ending Balance at Dec. 31, 2013	11,305,532		881,500		65,258			2,915	3,232,014				7,188,004	-64,159
Total comprehensive income	949,411												1,066,246	-116,835
Preferred stock cash dividends	-75,878												-75,878
Issuance of Series E preferred stock		346,500		350,000								-3,500
Exercise of stock warrants into common stock							85				-85
Stock-based compensation plans:
Compensation expense, net	45,434				128				45,306
Exercises of stock options, net	123,109				633				122,476
Stock purchase plan	9,588				43				9,545
Directors' stock plan	1,665				7				1,658
Deferred compensation plans, net, including dividend equivalents	-75				3			-307	345				-116
Other	1,747								1,747
Common stock cash dividends - $2.80 per share	-371,137												-371,137
Ending Balance at Dec. 31, 2014	$12,335,896		$1,231,500		$66,157			$2,608	$3,409,506				$7,807,119	($180,994)

Consolidated_Statement_of_Chan1

Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common stock per share dividend amount	$2.80	$2.80	$2.80
Common Stock [Member] | Series C Stock Warrants [Member]
Exercise of warrants into shares of common stock		407,542
Exercise of warrants into shares of common stock		186,589
Common Stock [Member] | Series A Warrants [Member]
Exercise of warrants into shares of common stock	427,905	69,127
Exercise of warrants into shares of common stock	169,543	25,427
Retained Earnings [Member]
Common stock per share dividend amount	$2.80	$2.80	$2.80

Significant_accounting_policie

Significant accounting policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Significant accounting policies	1.    Significant accounting policies
	M&T Bank Corporation (“M&T”) is a bank holding company headquartered in Buffalo, New York. Through subsidiaries, M&T provides individuals, corporations and other businesses, and institutions with commercial and retail banking services, including loans and deposits, trust, mortgage banking, asset management, insurance and other financial services. Banking activities are largely focused on consumers residing in New York State, Pennsylvania, Maryland, Delaware, Virginia and the District of Columbia and on small and medium-size businesses based in those areas. Banking services are also provided in West Virginia and New Jersey, while certain subsidiaries also conduct activities in other areas.
	The accounting and reporting policies of M&T and subsidiaries (“the Company”) conform to generally accepted accounting principles (“GAAP”) and to general practices within the banking industry. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The more significant accounting policies are as follows:
	Consolidation
	The consolidated financial statements include M&T and all of its subsidiaries. All significant intercompany accounts and transactions of consolidated subsidiaries have been eliminated in consolidation. The financial statements of M&T included in note 25 report investments in subsidiaries under the equity method. Information about some limited purpose entities that are affiliates of the Company but are not included in the consolidated financial statements appears in note 19.
	Consolidated Statement of Cash Flows
	For purposes of this statement, cash and due from banks and federal funds sold are considered cash and cash equivalents.
	Securities purchased under agreements to resell and securities sold under agreements to repurchase
	Securities purchased under agreements to resell and securities sold under agreements to repurchase are treated as collateralized financing transactions and are recorded at amounts equal to the cash or other consideration exchanged. It is generally the Company’s policy to take possession of collateral pledged to secure agreements to resell.
	Trading account
	Financial instruments used for trading purposes are stated at fair value. Realized gains and losses and unrealized changes in fair value of financial instruments utilized in trading activities are included in “trading account and foreign exchange gains” in the consolidated statement of income.
	Investment securities
	Investments in debt securities are classified as held to maturity and stated at amortized cost when management has the positive intent and ability to hold such securities to maturity. Investments in other debt securities and equity securities having readily determinable fair values are classified as available for sale and stated at estimated fair value. Amortization of premiums and accretion of discounts for investment securities available for sale and held to maturity are included in interest income.
	Other securities are stated at cost and include stock of the Federal Reserve Bank of New York and the Federal Home Loan Bank (“FHLB”) of New York.
	The cost basis of individual securities is written down through a charge to earnings when declines in value below amortized cost are considered to be other than temporary. In cases where fair value is less than amortized cost and the Company intends to sell a debt security, it is more likely than not to be required to sell a debt security before recovery of its amortized cost basis, or the Company does not expect to recover the entire amortized cost basis of a debt security, an other-than-temporary impairment is considered to have occurred. If the Company intends to sell the debt security or more likely than not will be required to sell the security before recovery of its amortized cost basis, the other-than-temporary impairment is recognized in earnings equal to the entire difference between the debt security’s amortized cost basis and its fair value. If the Company does not expect to recover the entire amortized cost basis of the security, the Company does not intend to sell the security and it is not more likely than not that the Company will be required to sell the security before recovery of its amortized cost basis, the other-than-temporary impairment is separated into (a) the amount representing the credit loss and (b) the amount related to all other factors. The amount of the other-than-temporary impairment related to the credit loss is recognized in earnings while the amount related to other factors is recognized in other comprehensive income, net of applicable taxes. Subsequently, the Company accounts for the other-than-temporarily impaired debt security as if the security had been purchased on the measurement date of the other-than-temporary impairment at an amortized cost basis equal to the previous amortized cost basis less the other-than-temporary impairment recognized in earnings. The cost basis of individual equity securities is written down to estimated fair value through a charge to earnings when declines in value below cost are considered to be other than temporary. Realized gains and losses on the sales of investment securities are determined using the specific identification method.
	Loans and leases
	The Company’s accounting methods for loans depends on whether the loans were originated by the Company or were acquired in a business combination.
	Originated loans and leases
	Interest income on loans is accrued on a level yield method. Loans are placed on nonaccrual status and previously accrued interest thereon is charged against income when principal or interest is delinquent 90 days, unless management determines that the loan status clearly warrants other treatment. Nonaccrual commercial loans and commercial real estate loans are returned to accrual status when borrowers have demonstrated an ability to repay their loans and there are no delinquent principal and interest payments. Consumer loans not secured by residential real estate are returned to accrual status when all past due principal and interest payments have been paid by the borrower. Loans secured by residential real estate are returned to accrual status when they are deemed to have an insignificant delay in payments of 90 days or less. Loan balances are charged off when it becomes evident that such balances are not fully collectible. For commercial loans and commercial real estate loans, charge-offs are recognized after an assessment by credit personnel of the capacity and willingness of the borrower to repay, the estimated value of any collateral, and any other potential sources of repayment. A charge-off is recognized when, after such assessment, it becomes evident that the loan balance is not fully collectible. For loans secured by residential real estate, the excess of the loan balances over the net realizable value of the property collateralizing the loan is charged-off when the loan becomes 150 days delinquent. Consumer loans are generally charged-off when the loans are 91 to 180 days past due, depending on whether the loan is collateralized and the status of repossession activities with respect to such collateral. Loan fees and certain direct loan origination costs are deferred and recognized as an interest yield adjustment over the life of the loan. Net deferred fees have been included in unearned discount as a reduction of loans outstanding. Commitments to sell real estate loans are utilized by the Company 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 recorded in the consolidated balance sheet includes changes in estimated fair market value during the hedge period, typically from the date of close through the sale date. Valuation adjustments made on these loans and commitments are included in “mortgage banking revenues.”
	Except for consumer and residential mortgage loans that are considered smaller balance homogenous loans and are evaluated collectively, the Company considers a loan to be impaired for purposes of applying GAAP when, based on current information and events, it is probable that the Company will be unable to collect all amounts according to the contractual terms of the loan agreement or the loan is delinquent 90 days. Regardless of loan type, the Company considers a loan to be impaired if it qualifies as a troubled debt restructuring. Impaired loans are classified as either nonaccrual or as loans renegotiated at below market rates which continue to accrue interest, provided that a credit assessment of the borrower’s financial condition results in an expectation of full repayment under the modified contractual terms. Certain loans greater than 90 days delinquent are not considered impaired if they are well-secured and in the process of collection. Loans less than 90 days delinquent are deemed to have an insignificant delay in payment and are generally not considered impaired. Impairment of a loan is measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate, the loan’s observable market price, or the fair value of collateral if the loan is collateral-dependent. Interest received on impaired loans placed on nonaccrual status is generally applied to reduce the carrying value of the loan or, if principal is considered fully collectible, recognized as interest income.
	Residual value estimates for commercial leases are generally determined through internal or external reviews of the leased property. The Company reviews commercial lease residual values at least annually and recognizes residual value impairments deemed to be other than temporary.
	Loans and leases acquired in a business combination
	Loans acquired in a business combination subsequent to December 31, 2008 are recorded at fair value with no carry-over of an acquired entity’s previously established allowance for credit losses. The excess of cash flows expected at acquisition over the estimated fair value of acquired loans is recognized as interest income over the remaining lives of the loans. Subsequent decreases in the expected principal cash flows require the Company to evaluate the need for additions to the Company’s allowance for credit losses. Subsequent improvements in expected cash flows result first in the recovery of any related allowance for credit losses and then in recognition of additional interest income over the then-remaining lives of the loans.
	Purchased impaired loans represent specifically identified loans with evidence of credit deterioration for which it was probable at acquisition that the Company would be unable to collect all contractual principal and interest payments.
	Allowance for credit losses
	The allowance for credit losses represents, in management’s judgment, the amount of losses inherent in the loan and lease portfolio as of the balance sheet date. The allowance is determined by management’s evaluation of the loan and lease portfolio based on such factors as the differing economic risks associated with each loan category, the current financial condition of specific borrowers, the economic environment in which borrowers operate, the level of delinquent loans, the value of any collateral and, where applicable, the existence of any guarantees or indemnifications. The effects of probable decreases in expected principal cash flows on acquired loans are also considered in the establishment of the allowance for credit losses.
	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 included in “other assets” in the consolidated balance sheet. Upon acquisition of assets taken in satisfaction of a defaulted loan, the excess of the remaining loan balance over the asset’s estimated fair value less costs to sell is charged off against the allowance for credit losses. Subsequent declines in value of the assets are recognized as “other costs of operations” in the consolidated statement of income.
	Premises and equipment
	Premises and equipment are stated at cost less accumulated depreciation. Depreciation expense is computed principally using the straight-line method over the estimated useful lives of the assets.
	Capitalized servicing rights
	Capitalized servicing assets are included in “other assets” in the consolidated balance sheet. Separately recognized servicing assets are initially measured at fair value. The Company uses the amortization method to subsequently measure servicing assets. Under that method, capitalized servicing assets are charged to expense in proportion to and over the period of estimated net servicing income.
	To estimate the fair value of servicing rights, the Company considers market prices for similar assets and the present value of expected future cash flows associated with the servicing rights calculated using assumptions that market participants would use in estimating future servicing income and expense. Such assumptions include estimates of the cost of servicing loans, loan default rates, an appropriate discount rate, and prepayment speeds. For purposes of evaluating and measuring impairment of capitalized servicing rights, the Company stratifies such assets based on the predominant risk characteristics of the underlying financial instruments that are expected to have the most impact on projected prepayments, cost of servicing and other factors affecting future cash flows associated with the servicing rights. Such factors may include financial asset or loan type, note rate and term. The amount of impairment recognized is the amount by which the carrying value of the capitalized servicing rights for a stratum exceeds estimated fair value. Impairment is recognized through a valuation allowance.
	Sales and securitizations of financial assets
	Transfers of financial assets for which the Company has surrendered control of the financial assets are accounted for as sales. Interests in a sale of financial assets that continue to be held by the Company, including servicing rights, are measured at fair value. The fair values of retained debt securities are generally determined through reference to independent pricing information. The fair values of retained servicing rights and any other retained interests are determined based on the present value of expected future cash flows associated with those interests and by reference to market prices for similar assets.
	Securitization structures typically require the use of special-purpose trusts that are considered variable interest entities. A variable interest entity is included in the consolidated financial statements if the Company has the power to direct the activities that most significantly impact the variable interest entity’s economic performance and has the obligation to absorb losses or the right to receive benefits of the variable interest entity that could potentially be significant to that entity.
	Goodwill and core deposit and other intangible assets
	Goodwill represents the excess of the cost of an acquired entity over the fair value of the identifiable net assets acquired. Goodwill is not amortized, but rather is tested for impairment at least annually at the reporting unit level, which is either at the same level or one level below an operating segment. Other acquired intangible assets with finite lives, such as core deposit intangibles, are initially recorded at estimated fair value and are amortized over their estimated lives. Core deposit and other intangible assets are generally amortized using accelerated methods over estimated useful lives of five to ten years. The Company periodically assesses whether events or changes in circumstances indicate that the carrying amounts of core deposit and other intangible assets may be impaired.
	Derivative financial instruments
	The Company accounts for derivative financial instruments at fair value. If certain conditions are met, a derivative may be specifically designated as (a) a hedge of the exposure to changes in the fair value of a recognized asset or liability or an unrecognized firm commitment, (b) a hedge of the exposure to variable cash flows of a forecasted transaction or (c) a hedge of the foreign currency exposure of a net investment in a foreign operation, an unrecognized firm commitment, an available-for-sale security, or a foreign currency denominated forecasted transaction.
	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. For such agreements, amounts receivable or payable are recognized as accrued under the terms of the agreement and the net differential is recorded as an adjustment to interest income or expense of the related asset or liability. Interest rate swap agreements may be designated as either fair value hedges or cash flow hedges. In a fair value hedge, the fair values of the interest rate swap agreements and changes in the fair values of the hedged items are recorded in the Company’s consolidated balance sheet with the corresponding gain or loss recognized in current earnings. The difference between changes in the fair values of interest rate swap agreements and the hedged items represents hedge ineffectiveness and is recorded in “other revenues from operations” in the consolidated statement of income. In a cash flow hedge, the effective portion of the derivative’s unrealized gain or loss is initially recorded as a component of other comprehensive income and subsequently reclassified into earnings when the forecasted transaction affects earnings. The ineffective portion of the unrealized gain or loss is reported in “other revenues from operations” immediately.
	The Company utilizes commitments to sell real estate loans to hedge the exposure to changes in the fair value of real estate loans held for sale. Commitments to originate real estate loans to be held for sale and commitments to sell real estate loans are generally recorded in the consolidated balance sheet at estimated fair market value.
	Derivative instruments not related to mortgage banking activities, including financial futures commitments and interest rate swap agreements, that do not satisfy the hedge accounting requirements are recorded at fair value and are generally classified as trading account assets or liabilities with resultant changes in fair value being recognized in “trading account and foreign exchange gains” in the consolidated statement of income.
	Stock-based compensation
	Stock-based compensation expense is recognized over the vesting period of the stock-based grant based on the estimated grant date value of the stock-based compensation that is expected to vest, except that the recognition of compensation costs is accelerated for stock-based awards granted to retirement-eligible employees and employees who will become retirement-eligible prior to full vesting of the award because the Company’s incentive compensation plan allows for vesting at the time an employee retires.
	Income taxes
	Deferred tax assets and liabilities are recognized for the future tax effects attributable to differences between the financial statement value of existing assets and liabilities and their respective tax bases and carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates and laws.
	The Company evaluates uncertain tax positions using the two-step process required by GAAP. The first step requires a determination of whether it is more likely than not that a tax position will be sustained upon examination, including resolution of any related appeals or litigation processes, based on the technical merits of the position. Under the second step, a tax position that meets the more-likely-than-not recognition threshold is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement.
	Earnings per common share
	Basic earnings per common share exclude dilution and are computed by dividing income available to common shareholders by the weighted-average number of common shares outstanding (exclusive of shares represented by the unvested portion of restricted stock and restricted stock unit grants) and common shares issuable under deferred compensation arrangements during the period. Diluted earnings per common share reflect shares represented by the unvested portion of restricted stock and restricted stock unit grants and the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in earnings. Proceeds assumed to have been received on such exercise or conversion are assumed to be used to purchase shares of M&T common stock at the average market price during the period, as required by the “treasury stock method” of accounting.
	GAAP requires that unvested share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents (whether paid or unpaid) shall be considered participating securities and 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 that contain such rights and, accordingly, the Company’s earnings per common share are calculated using the two-class method.
	Treasury stock
	Repurchases of shares of M&T common stock are recorded at cost as a reduction of shareholders’ equity. Reissuances of shares of treasury stock are recorded at average cost.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Acquisitions	2.    Acquisitions
	On August 27, 2012, M&T announced that it had entered into a definitive agreement with Hudson City Bancorp, Inc. (“Hudson City”), headquartered in Paramus, New Jersey, under which Hudson City would be acquired by M&T. Pursuant to the terms of the agreement, Hudson City shareholders will receive consideration for each common share of Hudson City in an amount valued at .08403 of an M&T share in the form of either M&T common stock or cash, based on the election of each Hudson City shareholder, subject to proration as specified in the merger agreement (which provides for an aggregate split of total consideration of 60% common stock of M&T and 40% cash). As of December 31, 2014 total consideration to be paid was valued at approximately $5.4 billion.
	At December 31, 2014, Hudson City had $36.6 billion of assets, including $21.7 billion of loans and $7.9 billion of investment securities, and $31.8 billion of liabilities, including $19.4 billion of deposits. The merger has received the approval of the common shareholders of M&T and Hudson City. However, the merger is subject to a number of other conditions, including regulatory approvals.
	On June 17, 2013, M&T and Manufacturers and Traders Trust Company (“M&T Bank”), M&T’s principal banking subsidiary, entered into a written agreement with the Federal Reserve Bank of New York (“Federal Reserve Bank”). Under the terms of the agreement, M&T and M&T Bank are required to submit to the Federal Reserve Bank a revised compliance risk management program designed to ensure compliance with the Bank Secrecy Act and anti-money-laundering laws and regulations and to take certain other steps to enhance their compliance practices. The Company commenced a major initiative, including the hiring of outside consulting firms, intended to fully address the Federal Reserve Bank’s concerns. In view of the timeframe required to implement this initiative, demonstrate its efficacy to the satisfaction of the Federal Reserve Bank and otherwise meet any other regulatory requirements that may be imposed in connection with these matters, M&T and Hudson City have extended the date after which either party may elect to terminate the merger agreement if the merger has not yet been completed to April 30, 2015. Nevertheless, there can be no assurances that the merger will be completed by that date.
	The Company incurred merger-related expenses in 2013 associated with the pending Hudson City acquisition and in 2012 associated with the May 16, 2011 acquisition of Wilmington Trust Corporation (“Wilmington Trust”) related to actual or planned systems conversions and other costs of integrating and conforming acquired operations with and into the Company. Those expenses consisted largely of professional services and other temporary help fees associated with the actual or planned conversion of systems and/or integration of operations; costs related to branch and office consolidations; costs related to termination of existing contractual arrangements for various services; initial marketing and promotion expenses designed to introduce M&T Bank to its new customers; severance (for former employees of Wilmington Trust) and incentive compensation costs; travel costs; and printing, postage, supplies and other costs of planning for or completing the transactions and commencing operations in new markets and offices.
	There were no merger-related expenses during 2014. A summary of merger-related expenses included in the consolidated statement of income for the years ended December 31, 2013 and 2012 follows:
		2013		2012
		(In thousands)
	Salaries and employee benefits	$	836	$	4,997
	Equipment and net occupancy		690		15
	Printing, postage and supplies		1,825		—
	Other costs of operations		9,013		4,867
		$	12,364	$	9,879

Investment_securities

Investment securities	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Investment securities	3.    Investment securities
	The amortized cost and estimated fair value of investment securities were as follows:
		Amortized		Gross			Gross		Estimated
		Cost		Unrealized			Unrealized		Fair  Value
				Gains			Losses
		(In thousands)
	December 31, 2014
	Investment securities available for sale:
	U.S. Treasury and federal agencies	$	161,408	$	544		$	5	$	161,947
	Obligations of states and political subdivisions		8,027		224			53		8,198
	Mortgage-backed securities:
	Government issued or guaranteed		8,507,571		223,889			337		8,731,123
	Privately issued		104		2			3		103
	Collateralized debt obligations		30,073		21,276			1,033		50,316
	Other debt securities		138,240		1,896			18,648		121,488
	Equity securities		73,901		11,020			1,164		83,757
			8,919,324		258,851			21,243		9,156,932
	Investment securities held to maturity:
	Obligations of states and political subdivisions		148,961		2,551			189		151,323
	Mortgage-backed securities:
	Government issued or guaranteed		3,149,320		78,485			7,000		3,220,805
	Privately issued		201,733		1,143			44,576		158,300
	Other debt securities		7,854		—			—		7,854
			3,507,868		82,179			51,765		3,538,282
	Other securities		328,742		—			—		328,742
	Total	$	12,755,934	$	341,030		$	73,008	$	13,023,956
	December 31, 2013
	Investment securities available for sale:
	U.S. Treasury and federal agencies	$	37,396	$	382		$	2	$	37,776
	Obligations of states and political subdivisions		10,484		333			6		10,811
	Mortgage-backed securities:
	Government issued or guaranteed		4,123,435		61,001			19,350		4,165,086
	Privately issued		1,468		387			5		1,850
	Collateralized debt obligations		42,274		21,666			857		63,083
	Other debt securities		137,828		1,722			19,465		120,085
	Equity securities		91,480		41,842			227		133,095
			4,444,365		127,333			39,912		4,531,786
	Investment securities held to maturity:
	Obligations of states and political subdivisions		169,684		3,744			135		173,293
	Mortgage-backed securities:
	Government issued or guaranteed		3,567,905		16,160			65,149		3,518,916
	Privately issued		219,628		—			60,623		159,005
	Other debt securities		8,913		—			—		8,913
			3,966,130		19,904			125,907		3,860,127
	Other securities		298,581		—			—		298,581
	Total	$	8,709,076	$	147,237		$	165,819	$	8,690,494
	No investment in securities of a single non-U.S. Government or government agency issuer exceeded ten percent of shareholders’ equity at December 31, 2014.
	As of December 31, 2014, the latest available investment ratings of all obligations of states and political subdivisions, privately issued mortgage-backed securities, collateralized debt obligations and other debt securities were:
		Amortized		Estimated			Average Credit Rating of Fair Value Amount
		Cost		Fair  Value			A or Better		BBB			BB		B or Less		Not Rated
		(In thousands)
	Obligations of states and political subdivisions	$	156,988	$	159,521		$	137,606	$	—		$	—	$	—	$	21,915
	Privately issued mortgage-backed securities		201,837		158,403			48,368		19			—		109,949		67
	Collateralized debt obligations		30,073		50,316			6,629		5,488			1,273		36,926		—
	Other debt securities		146,094		129,342			12,352		58,481			29,028		20,400		9,081
	Total	$	534,992	$	497,582		$	204,955	$	63,988		$	30,301	$	167,275	$	31,063
	The amortized cost and estimated fair value of collateralized mortgage obligations included in mortgage-backed securities were as follows:
		December 31
		2014		2013
		(In thousands)
	Collateralized mortgage obligations:
	Amortized cost	$	209,107	$	231,040
	Estimated fair value		165,860		171,100
	Gross realized gains from sales of investment securities were $116,490,000 in 2013. During 2013, the Company sold its holdings of Visa Class B shares for a gain of $89,545,000 and its holdings of MasterCard Class B shares for a gain of $13,208,000. Gross realized losses on investment securities were $60,033,000 in 2013. The Company sold substantially all of its privately issued mortgage-backed securities held in the available-for-sale investment securities portfolio during 2013. In total, $1.0 billion of such securities were sold for a net loss of approximately $46,302,000. Gross realized gains and losses from sales of investment securities were not significant in 2014 or 2012.
The Company recognized $10 million and $48 million of pre-tax other-than-temporary impairment losses related to privately issued mortgage-backed securities in 2013 and 2012, respectively. The impairment charges were recognized in light of deterioration of real estate values and a rise in delinquencies and charge-offs of underlying mortgage loans collateralizing those securities. The other-than-temporary impairment losses represented management’s estimate of credit losses inherent in the debt securities considering projected cash flows using assumptions for delinquency rates, loss severities, and other estimates of future collateral performance. There were no other-than-temporary impairment losses in 2014.
At December 31, 2014, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:
	Amortized		Estimated
	Cost		Fair Value
	(In thousands)
Debt securities available for sale:
Due in one year or less	$	7,412	$	7,468
Due after one year through five years		164,412		165,340
Due after five years through ten years		3,524		3,577
Due after ten years		162,400		165,564
		337,748		341,949
Mortgage-backed securities available for sale		8,507,675		8,731,226
	$	8,845,423	$	9,073,175
Debt securities held to maturity:
Due in one year or less	$	23,107	$	23,254
Due after one year through five years		84,112		85,457
Due after five years through ten years		41,742		42,612
Due after ten years		7,854		7,854
		156,815		159,177
Mortgage-backed securities held to maturity		3,351,053		3,379,105
	$	3,507,868	$	3,538,282
A summary of investment securities that as of December 31, 2014 and 2013 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			Fair Value		Unrealized
			Losses					Losses
	(In thousands)
December 31, 2014
Investment securities available for sale:
U.S. Treasury and federal agencies	$	6,505	$	(5	)	$	—	$	—
Obligations of states and political subdivisions		1,785		(52	)		121		(1	)
Mortgage-backed securities:
Government issued or guaranteed		39,001		(186	)		5,555		(151	)
Privately issued		—		—			65		(3	)
Collateralized debt obligations		2,108		(696	)		5,512		(337	)
Other debt securities		14,017		(556	)		92,661		(18,092	)
Equity securities		2,138		(1,164	)		—		—
		65,554		(2,659	)		103,914		(18,584	)
Investment securities held to maturity:
Obligations of states and political subdivisions		29,886		(184	)		268		(5	)
Mortgage-backed securities:
Government issued or guaranteed		137,413		(361	)		446,780		(6,639	)
Privately issued		—		—			127,512		(44,576	)
		167,299		(545	)		574,560		(51,220	)
Total	$	232,853	$	(3,204	)	$	678,474	$	(69,804	)
December 31, 2013
Investment securities available for sale:
U.S. Treasury and federal agencies	$	745	$	(2	)	$	—	$	—
Obligations of states and political subdivisions		—		—			558		(6	)
Mortgage-backed securities:
Government issued or guaranteed		1,697,094		(19,225	)		5,815		(125	)
Privately issued		—		—			98		(5	)
Collateralized debt obligations		—		—			6,257		(857	)
Other debt securities		1,428		(4	)		103,602		(19,461	)
Equity securities		159		(227	)		—		—
		1,699,426		(19,458	)		116,330		(20,454	)
Investment securities held to maturity:
Obligations of states and political subdivisions		13,517		(120	)		1,558		(15	)
Mortgage-backed securities:
Government issued or guaranteed		2,629,950		(65,149	)		—		—
Privately issued		—		—			159,005		(60,623	)
		2,643,467		(65,269	)		160,563		(60,638	)
Total	$	4,342,893	$	(84,727	)	$	276,893	$	(81,092	)
The Company owned 296 individual investment securities with aggregate gross unrealized losses of $73 million at December 31, 2014. Based on a review of each of the securities in the investment securities portfolio at December 31, 2014, the Company concluded that it expected to recover the amortized cost basis of its investment. As of December 31, 2014, 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 December 31, 2014, the Company has not identified events or changes in circumstances which may have a significant adverse effect on the fair value of the $329 million of cost method investment securities.
At December 31, 2014, investment securities with a carrying value of $3,825,003,000, including $2,905,457,000 of investment securities available for sale, were pledged to secure borrowings from various FHLBs, repurchase agreements, governmental deposits, interest rate swap agreements and available lines of credit as described in note 9.
Investment securities pledged by the Company to secure obligations whereby the secured party is permitted by contract or custom to sell or repledge such collateral totaled $1,631,267,000 at December 31, 2014. The pledged securities included securities of the U.S. Treasury and federal agencies and mortgage-backed securities.

Loans_and_leases

Loans and leases	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Loans and leases	4.    Loans and leases
	Total loans and leases outstanding were comprised of the following:
			December 31
			2014			2013
			(In thousands)
	Loans
	Commercial, financial, etc.		$	18,280,049		$	17,477,238
	Real estate:
	Residential			8,636,794			8,911,554
	Commercial			22,614,174			21,799,886
	Construction			5,061,269			4,457,650
	Consumer			10,969,879			10,280,527
	Total loans			65,562,165			62,926,855
	Leases
	Commercial			1,337,204			1,398,928
	Total loans and leases			66,899,369			64,325,783
	Less: unearned discount			(230,413	)		(252,624	)
	Total loans and leases, net of unearned discount		$	66,668,956		$	64,073,159
	One-to-four family residential mortgage loans held for sale were $435 million at December 31, 2014 and $401 million at December 31, 2013. Commercial real estate loans held for sale were $308 million at December 31, 2014 and $68 million at December 31, 2013.
	During 2013, the Company securitized approximately $1.3 billion of one-to-four family residential real estate loans previously held in the Company’s loan portfolio into guaranteed mortgage-backed securities with the Government National Mortgage Association (“Ginnie Mae”) and recognized gains of $42,382,000. In addition, the Company securitized and sold in 2013 approximately $1.4 billion of automobile loans held in its loan portfolio, resulting in a gain of $20,683,000.
	As of December 31, 2014, approximately $2.4 billion of commercial real estate loan balances serviced for others had been sold with recourse in conjunction with the Company’s participation in the Fannie Mae Delegated Underwriting and Servicing (“DUS”) program. At December 31, 2014, the Company estimated that the recourse obligations described above were not material to the Company’s consolidated financial position. There have been no material losses incurred as a result of those credit recourse arrangements.
	In addition to recourse obligations, as described in note 21, 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. Charges incurred for such obligation, which are recorded as a reduction of mortgage banking revenues, were $4 million, $17 million and $28 million in 2014, 2013 and 2012, respectively.
	The outstanding principal balance and the carrying amount of acquired loans that were recorded at fair value at the acquisition date that is included in the consolidated balance sheet were as follows:
			December 31
			2014			2013
			(In thousands)
	Outstanding principal balance		$	3,070,268		$	4,656,811
	Carrying amount:
	Commercial, financial, leasing, etc.			247,820			580,685
	Commercial real estate			961,828			1,541,368
	Residential real estate			453,360			576,473
	Consumer			933,537			1,308,926
			$	2,596,545		$	4,007,452
	Purchased impaired loans included in the table above totaled $198 million at December 31, 2014 and $331 million at December 31, 2013, representing less than 1% of the Company’s assets as of each date. A summary of changes in the accretable yield for acquired loans for the years ended December 31, 2014, 2013 and 2012 follows:
	For Year Ended December 31,		2014						2013						2012
			Purchased			Other			Purchased			Other			Purchased			Other
			Impaired			Acquired			Impaired			Acquired			Impaired			Acquired
			(In thousands)
	Balance at beginning of period		$	37,230		$	538,633		$	42,252		$	638,272		$	30,805		$	807,960
	Interest income			(21,263	)		(178,670	)		(36,727	)		(247,295	)		(40,551	)		(295,654	)
	Reclassifications from nonaccretable balance, net			60,551			24,907			31,705			149,595			51,998			148,490
	Other(a)			—			12,509			—			(1,939	)		—			(22,524	)
	Balance at end of period		$	76,518		$	397,379		$	37,230		$	538,633		$	42,252		$	638,272
	(a)	Other changes in expected cash flows including changes in interest rates and prepayment assumptions.
	A summary of current, past due and nonaccrual loans as of December 31, 2014 and 2013 follows:
									90 Days or More Past
									Due and Accruing
			Current			30-89 Days			Non-			Acquired(a)			Purchased			Nonaccrual			Total
						Past Due			acquired						Impaired(b)
			(In thousands)
	December 31, 2014
	Commercial, financial, leasing, etc.		$	19,228,265		$	37,246		$	1,805		$	6,231		$	10,300		$	177,445		$	19,461,292
	Real estate:
	Commercial			22,208,491			118,704			22,170			14,662			51,312			141,600			22,556,939
	Residential builder and developer			1,273,607			11,827			492			9,350			98,347			71,517			1,465,140
	Other commercial construction			3,484,932			17,678			—			—			17,181			25,699			3,545,490
	Residential			7,640,368			226,932			216,489			35,726			18,223			180,275			8,318,013
	Residential Alt-A			249,810			11,774			—			—			—			77,704			339,288
	Consumer:
	Home equity lines and loans			5,859,378			42,945			—			27,896			2,374			89,291			6,021,884
	Automobile			1,931,138			30,500			—			133			—			17,578			1,979,349
	Other			2,909,791			33,295			4,064			16,369			—			18,042			2,981,561
	Total		$	64,785,780		$	530,901		$	245,020		$	110,367		$	197,737		$	799,151		$	66,668,956
	December 31, 2013
Commercial, financial, leasing, etc.		$	18,489,474		$	77,538		$	4,981		$	6,778		$	15,706		$	110,739		$	18,705,216
Real estate:
Commercial			21,236,071			145,749			63,353			35,603			88,034			173,048			21,741,858
Residential builder and developer			1,025,984			8,486			141			7,930			137,544			96,427			1,276,512
Other commercial construction			2,986,598			42,234			—			8,031			57,707			35,268			3,129,838
Residential			7,630,368			295,131			294,649			43,700			29,184			252,805			8,545,837
Residential Alt-A			283,253			18,009			—			—			—			81,122			382,384
Consumer:
Home equity lines and loans			5,972,365			40,537			—			27,754			2,617			78,516			6,121,789
Automobile			1,314,246			29,144			—			366			—			21,144			1,364,900
Other			2,726,522			47,830			5,386			—			—			25,087			2,804,825
Total		$	61,664,881		$	704,658		$	368,510		$	130,162		$	330,792		$	874,156		$	64,073,159
(a)	Acquired loans that were recorded at fair value at acquisition date. This category does not include purchased impaired loans that are presented separately.
(b)	Accruing loans that were impaired at acquisition date and were recorded at fair value.
If nonaccrual and renegotiated loans had been accruing interest at their originally contracted terms, interest income on such loans would have amounted to $58,314,000 in 2014, $62,010,000 in 2013 and $69,054,000 in 2012. The actual amounts included in interest income during 2014, 2013 and 2012 on such loans were $28,492,000, $31,987,000 and $30,484,000, respectively.
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.
The table below summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the year ended December 31, 2014:
					Recorded Investment						Financial Effects of
											Modification
		Number			Pre-			Post-			Recorded			Interest
					modifica-			modifica-			Investment			(b)
					tion			tion			(a)
		(Dollars in thousands)
Commercial, financial, leasing, etc.
Principal deferral			95		$	29,035		$	23,628		$	(5,407	)	$	—
Other			3			29,912			31,604			1,692			—
Combination of concession types			7			19,167			19,030			(137	)		(20	)
Real estate:
Commercial
Principal deferral			39			19,077			18,997			(80	)		—
Interest rate reduction			1			255			252			(3	)		(48	)
Other			1			650			—			(650	)		—
Combination of concession types			7			1,152			1,198			46			(264	)
Residential builder and developer
Principal deferral			2			1,639			1,639			—			—
Other commercial construction
Principal deferral			4			6,703			6,611			(92	)		—
Residential
Principal deferral			28			2,710			2,905			195			—
Interest rate reduction			11			1,146			1,222			76			(152	)
Other			1			188			188			—			—
Combination of concession types			30			4,211			4,287			76			(483	)
Residential Alt-A
Principal deferral			6			880			963			83			—
Combination of concession types			21			3,806			3,846			40			(386	)
Consumer:
Home equity lines and loans
Principal deferral			3			280			280			—			—
Interest rate reduction			6			535			535			—			(120	)
Combination of concession types			47			5,031			5,031			—			(560	)
Automobile
Principal deferral			208			3,293			3,293			—			—
Interest rate reduction			9			152			152			—			(12	)
Other			42			255			255			—			—
Combination of concession types			81			1,189			1,189			—			(100	)
Other
Principal deferral			33			245			245			—			—
Interest rate reduction			4			293			293			—			(63	)
Other			1			45			45			—			—
Combination of concession types			70			2,502			2,502			—			(761	)
Total			760		$	134,351		$	130,190		$	(4,161	)	$	(2,969	)
(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages.
(b)	Represents the present value of interest rate concessions discounted at the effective rate of the original loan.
The table below summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the year ended December 31, 2013:
					Recorded Investment						Financial Effects of
											Modification
		Number			Pre-			Post-			Recorded			Interest
					modifica-			modifica-			Investment			(b)
					tion			tion			(a)
		(Dollars in thousands)
Commercial, financial, leasing, etc.
Principal deferral			79		$	16,389		$	16,002		$	(387	)	$	—
Interest rate reduction			1			104			335			231			(54	)
Other			4			50,433			50,924			491			—
Combination of concession types			11			6,229			5,578			(651	)		(458	)
Real estate:
Commercial
Principal deferral			27			40,639			40,464			(175	)		—
Other			2			449			475			26			—
Combination of concession types			9			2,649			3,040			391			(250	)
Residential builder and developer
Principal deferral			18			21,423			20,577			(846	)		—
Other			1			4,039			3,888			(151	)		—
Combination of concession types			3			15,580			15,514			(66	)		(535	)
Other commercial construction
Principal deferral			3			590			521			(69	)		—
Residential
Principal deferral			32			3,556			3,821			265			—
Other			1			195			195			—			—
Combination of concession types			61			73,940			70,854			(3,086	)		(924	)
Residential Alt-A
Principal deferral			10			1,900			1,880			(20	)		—
Combination of concession types			19			2,826			3,148			322			(790	)
Consumer:
Home equity lines and loans
Principal deferral			10			859			861			2			—
Interest rate reduction			1			99			99			—			(8	)
Other			1			106			106			—			—
Combination of concession types			28			2,190			2,190			—			(270	)
Automobile
Principal deferral			460			6,148			6,148			—			—
Interest rate reduction			15			235			235			—			(22	)
Other			78			339			339			—			—
Combination of concession types			225			2,552			2,552			—			(191	)
Other
Principal deferral			36			332			332			—			—
Interest rate reduction			1			12			12			—			(2	)
Other			2			14			14			—			—
Combination of concession types			120			4,248			4,248			—			(1,187	)
Total			1,258		$	258,075		$	254,352		$	(3,723	)	$	(4,691	)
(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages.
(b)	Represents the present value of interest rate concessions discounted at the effective rate of the original loan.
The table below summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the year ended December 31, 2012:
					Recorded Investment						Financial Effects of
											Modification
		Number			Pre-			Post-			Recorded			Interest
					modifica-			modifica-			Investment			(b)
					tion			tion			(a)
		(Dollars in thousands)
Commercial, financial, leasing, etc.
Principal deferral			61		$	23,888		$	22,456		$	(1,432	)	$	—
Other			3			2,967			3,052			85			—
Combination of concession types			5			628			740			112			(102	)
Real estate:
Commercial
Principal deferral			24			22,855			23,059			204			—
Interest rate reduction			2			665			708			43			(129	)
Combination of concession types			7			1,637			1,656			19			(351	)
Residential builder and developer
Principal deferral			23			36,868			34,740			(2,128	)		—
Combination of concession types			7			37,602			36,148			(1,454	)		—
Other commercial construction
Principal deferral			6			81,062			79,312			(1,750	)		—
Residential
Principal deferral			36			4,643			4,808			165			—
Interest rate reduction			1			109			109			—			(20	)
Combination of concession types			62			12,886			13,146			260			(657	)
Residential Alt-A
Principal deferral			7			968			989			21			—
Combination of concession types			38			8,525			8,717			192			(159	)
Consumer:
Home equity lines and loans
Principal deferral			15			1,285			1,285			—			—
Interest rate reduction			1			144			144			—			(6	)
Combination of concession types			29			2,332			2,332			—			(368	)
Automobile
Principal deferral			618			8,347			8,347			—			—
Interest rate reduction			22			328			328			—			(24	)
Other			67			300			300			—			—
Combination of concession types			375			5,857			5,857			—			(684	)
Other
Principal deferral			80			1,201			1,201			—			—
Interest rate reduction			22			515			515			—			(85	)
Other			13			54			54			—			—
Combination of concession types			84			1,015			1,015			—			(268	)
Total			1,608		$	256,681		$	251,018		$	(5,663	)	$	(2,853	)
(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages.
(b)	Represents the present value of interest rate concessions discounted at the effective rate of the original loan.
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 December 31, 2014, 2013 and 2012 and for which there was a subsequent payment default during the respective period were not material.
Borrowings by directors and certain officers of M&T and its banking subsidiaries, and by associates of such persons, exclusive of loans aggregating less than $120,000, amounted to $49,799,000 and $135,512,000 at December 31, 2014 and 2013, respectively. During 2014, new borrowings by such persons amounted to $12,327,000 (including any borrowings of new directors or officers that were outstanding at the time of their election) and repayments and other reductions (including reductions resulting from retirements) were $98,040,000.
At December 31, 2014, approximately $10.4 billion of commercial loans and leases, $9.7 billion of commercial real estate loans, $5.3 billion of one-to-four family residential real estate loans, $4.3 billion of home equity loans and lines of credit and $2.9 billion of other consumer loans were pledged to secure outstanding borrowings from the FHLB of New York and available lines of credit as described in note 9.
The Company’s loan and lease portfolio includes commercial lease financing receivables consisting of direct financing and leveraged leases for machinery and equipment, railroad equipment, commercial trucks and trailers, and aircraft. A summary of lease financing receivables follows:
		December 31
		2014			2013
		(In thousands)
Commercial leases:
Direct financings:
Lease payments receivable		$	1,022,133		$	1,052,214
Estimated residual value of leased assets			79,525			85,595
Unearned income			(103,777	)		(114,101	)
Investment in direct financings			997,881			1,023,708
Leveraged leases:
Lease payments receivable			102,457			127,821
Estimated residual value of leased assets			133,089			133,298
Unearned income			(44,288	)		(47,188	)
Investment in leveraged leases			191,258			213,931
Total investment in leases.		$	1,189,139		$	1,237,639
Deferred taxes payable arising from leveraged leases		$	169,101		$	172,296
Included within the estimated residual value of leased assets at December 31, 2014 and 2013 were $48 million and $54 million, respectively, in residual value associated with direct financing leases that are guaranteed by the lessees or others.
At December 31, 2014, the minimum future lease payments to be received from lease financings were as follows:
		(In thousands)
Year ending December 31:
2015		$	268,086
2016			242,248
2017			177,539
2018			127,985
2019			92,205
Later years			216,527
		$	1,124,590

Allowance_for_credit_losses

Allowance for credit losses	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Allowance for credit losses	5.    Allowance for credit losses
	Changes in the allowance for credit losses for the years ended December 31, 2014, 2013 and 2012 were as follows:
		Commercial,			Real Estate
		Financial,
	2014	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
		(In thousands)
	Beginning balance	$	273,383		$	324,978		$	78,656		$	164,644		$	75,015	$	916,676
	Provision for credit losses		51,410			(13,779	)		(3,974	)		89,704			639		124,000
	Net charge-offs
	Charge-offs		(58,943	)		(14,058	)		(21,351	)		(84,390	)		—		(178,742	)
	Recoveries		22,188			10,786			8,579			16,075			—		57,628
	Net charge-offs		(36,755	)		(3,272	)		(12,772	)		(68,315	)		—		(121,114	)
	Ending balance	$	288,038		$	307,927		$	61,910		$	186,033		$	75,654	$	919,562
	2013
	Beginning balance	$	246,759		$	337,101		$	88,807		$	179,418		$	73,775	$	925,860
	Provision for credit losses		124,180			275			3,149			56,156			1,240		185,000
	Allowance related to loans sold or securitized		—			—			—			(11,000	)		—		(11,000	)
	Net charge-offs
	Charge-offs		(109,329	)		(34,595	)		(23,621	)		(85,965	)		—		(253,510	)
	Recoveries		11,773			22,197			10,321			26,035			—		70,326
	Net charge-offs		(97,556	)		(12,398	)		(13,300	)		(59,930	)		—		(183,184	)
	Ending balance	$	273,383		$	324,978		$	78,656		$	164,644		$	75,015	$	916,676
	2012
	Beginning balance	$	234,022		$	367,637		$	91,915		$	143,121		$	71,595	$	908,290
	Provision for credit losses		42,510			5,211			34,864			119,235			2,180		204,000
	Net charge-offs
	Charge-offs		(41,148	)		(41,945	)		(44,314	)		(103,348	)		—		(230,755	)
	Recoveries		11,375			6,198			6,342			20,410			—		44,325
	Net charge-offs		(29,773	)		(35,747	)		(37,972	)		(82,938	)		—		(186,430	)
	Ending balance	$	246,759		$	337,101		$	88,807		$	179,418		$	73,775	$	925,860
	Despite the above allocation, the allowance for credit losses is general in nature and is available to absorb losses from any loan or lease type.
	In establishing the allowance for credit losses, the Company estimates losses attributable to specific troubled credits identified through both normal and detailed or intensified credit review processes and also estimates losses inherent in other loans and leases on a collective basis. For purposes of determining the level of the allowance for credit losses, the Company evaluates its loan and lease portfolio by loan type. The amounts of loss components in the Company’s loan and lease portfolios are determined through a loan by loan analysis of larger balance commercial and commercial real estate loans that are in nonaccrual status and by applying loss factors to groups of loan balances based on loan type and management’s classification of such loans under the Company’s loan grading system. Measurement of the specific loss components is typically based on expected future cash flows, collateral values and other factors that may impact the borrower’s ability to pay. In determining the allowance for credit losses, the Company utilizes a loan grading system which is applied to commercial and commercial real estate credits on an individual loan basis. Loan officers are responsible for continually assigning grades to these loans based on standards outlined in the Company’s Credit Policy. Internal loan grades are also monitored by the Company’s loan review department to ensure consistency and strict adherence to the prescribed standards. Loan grades are assigned loss component factors that reflect the Company’s loss estimate for each group of loans and leases. Factors considered in assigning loan grades and loss component factors include borrower-specific information related to expected future cash flows and operating results, collateral values, geographic location, financial condition and performance, payment status, and other information; levels of and trends in portfolio charge-offs and recoveries; levels of and trends in portfolio delinquencies and impaired loans; changes in the risk profile of specific portfolios; trends in volume and terms of loans; effects of changes in credit concentrations; and observed trends and practices in the banking industry. As updated appraisals are obtained on individual loans or other events in the market place indicate that collateral values have significantly changed, individual loan grades are adjusted as appropriate. Changes in other factors cited may also lead to loan grade changes at any time. Except for consumer and residential real estate loans that are considered smaller balance homogenous loans and acquired loans that are evaluated on an aggregated basis, the Company considers a loan to be impaired for purposes of applying GAAP when, based on current information and events, it is probable that the Company will be unable to collect all amounts according to the contractual terms of the loan agreement or the loan is delinquent 90 days. Regardless of loan type, the Company considers a loan to be impaired if it qualifies as a troubled debt restructuring. Modified loans, including smaller balance homogenous loans, that are considered to be troubled debt restructurings are evaluated for impairment giving consideration to the impact of the modified loan terms on the present value of the loan’s expected cash flows.
	The following tables provide information with respect to loans and leases that were considered impaired as of December 31, 2014 and 2013 and for the years ended December 31, 2014, 2013 and 2012.
		December 31, 2014									December 31, 2013
		Recorded			Unpaid			Related			Recorded			Unpaid		Related
		Investment			Principal			Allowance			Investment			Principal		Allowance
					Balance									Balance
		(In thousands)
	With an allowance recorded:
	Commercial, financial, leasing, etc.	$	132,340		$	165,146		$	31,779		$	90,293		$	112,092	$	24,614
	Real estate:
	Commercial		83,955			96,209			14,121			113,570			132,325		19,520
	Residential builder and developer		17,632			22,044			805			33,311			55,122		4,379
	Other commercial construction		5,480			6,484			900			86,260			90,515		4,022
	Residential		88,970			107,343			4,296			96,508			114,521		7,146
	Residential Alt-A		101,137			114,565			11,000			111,911			124,528		14,000
	Consumer:
	Home equity lines and loans		19,771			20,806			6,213			13,672			14,796		3,312
	Automobile		30,317			30,317			8,070			40,441			40,441		11,074
	Other		18,973			18,973			5,459			17,660			17,660		4,541
			498,575			581,887			82,643			603,626			702,000		92,608
	With no related allowance recorded:
	Commercial, financial, leasing, etc.		73,978			81,493			—			28,093			33,095		—
	Real estate:
	Commercial		66,777			78,943			—			65,271			84,333		—
	Residential builder and developer		58,820			96,722			—			72,366			104,768		—
	Other commercial construction		20,738			41,035			—			7,369			11,493		—
	Residential		16,815			26,750			—			84,144			95,358		—
	Residential Alt-A		26,752			46,964			—			28,357			52,211		—
			263,880			371,907			—			285,600			381,258		—
	Total:
	Commercial, financial, leasing, etc.		206,318			246,639			31,779			118,386			145,187		24,614
	Real estate:
	Commercial		150,732			175,152			14,121			178,841			216,658		19,520
Residential builder and developer		76,452			118,766			805			105,677			159,890		4,379
Other commercial construction		26,218			47,519			900			93,629			102,008		4,022
Residential		105,785			134,093			4,296			180,652			209,879		7,146
Residential Alt-A		127,889			161,529			11,000			140,268			176,739		14,000
Consumer:
Home equity lines and loans		19,771			20,806			6,213			13,672			14,796		3,312
Automobile		30,317			30,317			8,070			40,441			40,441		11,074
Other		18,973			18,973			5,459			17,660			17,660		4,541
Total	$	762,455		$	953,794		$	82,643		$	889,226		$	1,083,258	$	92,608
	Year Ended									Year Ended
	December 31, 2014									December 31, 2013
	Average			Interest Income						Average			Interest Income
	Recorded			Recognized						Recorded			Recognized
	Investment			Total			Cash			Investment			Total		Cash
							Basis								Basis
	(In thousands)
Commercial, financial, leasing, etc.	$	181,932		$	2,251		$	2,251		$	155,188		$	7,197	$	7,197
Real estate:
Commercial		184,773			4,029			4,029			197,533			4,852		4,852
Residential builder and developer		91,149			142			142			147,288			1,043		796
Other commercial construction		62,734			1,893			1,893			96,475			5,248		5,248
Residential		126,005			9,180			6,978			183,059			6,203		4,111
Residential Alt-A		133,800			6,613			2,546			149,461			6,784		2,341
Consumer:
Home equity lines and loans		18,083			750			248			12,811			683		183
Automobile		35,173			2,251			295			44,116			2,916		515
Other		18,378			690			191			15,710			634		208
Total	$	852,027		$	27,799		$	18,573		$	1,001,641		$	35,560	$	25,451
	Year Ended
	December 31, 2012
				Interest Income
				Recognized
	Average			Total			Cash
	Recorded						Basis
	Investment
	(In thousands)
Commercial, financial, leasing, etc.	$	151,314		$	2,938		$	2,938
Real estate:
Commercial		185,171			2,834			2,834
Residential builder and developer		249,191			1,563			1,102
Other commercial construction		99,672			5,020			5,020
Residential		132,888			5,284			3,300
Residential Alt-A		171,546			7,175			2,226
Consumer:
Home equity lines and loans		11,322			663			179
Automobile		51,650			3,470			724
Other		11,028			472			197
Total	$	1,063,782		$	29,419		$	18,520
In accordance with the previously described policies, the Company utilizes a loan grading system that is applied to all commercial loans and commercial real estate loans. Loan grades are utilized to differentiate risk within the portfolio and consider the expectations of default for each loan. Commercial loans and commercial real estate loans with a lower expectation of default are assigned one of ten possible “pass” loan grades and are generally ascribed lower loss factors when determining the allowance for credit losses. Loans with an elevated level of credit risk are classified as “criticized” and are ascribed a higher loss factor when determining the allowance for credit losses. Criticized loans may be classified as “nonaccrual” if the Company no longer expects to collect all amounts according to the contractual terms of the loan agreement or the loan is delinquent 90 days or more. All larger balance criticized commercial loans and commercial real estate loans are individually reviewed by centralized loan review personnel each quarter to determine the appropriateness of the assigned loan grade, including whether the loan should be reported as accruing or nonaccruing. Smaller balance criticized loans are analyzed by business line risk management areas to ensure proper loan grade classification. Furthermore, criticized nonaccrual commercial loans and commercial real estate loans are considered impaired and, as a result, specific loss allowances on such loans are established within the allowance for credit losses to the extent appropriate in each individual instance. The following table summarizes the loan grades applied to the various classes of the Company’s commercial loans and commercial real estate loans.
				Real Estate
	Commercial,			Commercial			Residential			Other
	Financial,						Builder and			Commercial
	Leasing, etc						Developer			Construction
	(In thousands)
December 31, 2014
Pass	$	18,695,440		$	21,837,022		$	1,347,778		$	3,347,522
Criticized accrual		588,407			578,317			45,845			172,269
Criticized nonaccrual		177,445			141,600			71,517			25,699
Total	$	19,461,292		$	22,556,939		$	1,465,140		$	3,545,490
December 31, 2013
Pass	$	17,894,592		$	20,972,257		$	1,107,144		$	3,040,106
Criticized accrual		699,885			596,553			72,941			54,464
Criticized nonaccrual		110,739			173,048			96,427			35,268
Total	$	18,705,216		$	21,741,858		$	1,276,512		$	3,129,838
In determining the allowance for credit losses, residential real estate loans and consumer loans are generally evaluated collectively after considering such factors as payment performance and recent loss experience and trends, which are mainly driven by current collateral values in the market place as well as the amount of loan defaults. Loss rates on such loans are determined by reference to recent charge-off history and are evaluated (and adjusted if deemed appropriate) through consideration of other factors including near-term forecasted loss estimates developed by the Company’s Credit Department. In arriving at such forecasts, the Company considers the current estimated fair value of its collateral based on geographical adjustments for home price depreciation/appreciation and overall borrower repayment performance. With regard to collateral values, the realizability of such values by the Company contemplates repayment of any first lien position prior to recovering amounts on a second lien position. However, residential real estate loans and outstanding balances of home equity loans and lines of credit that are more than 150 days past due are generally evaluated for collectibility on a loan-by-loan basis giving consideration to estimated collateral values. The carrying value of residential real estate loans and home equity loans and lines of credit for which a partial charge-off has been recognized aggregated $63 million and $18 million, respectively, at December 31, 2014 and $58 million and $18 million, respectively, at December 31, 2013. 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 totaled $27 million and $28 million, respectively, at December 31, 2014 and $26 million and $21 million, respectively, at December 31, 2013.
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.
The allocation of the allowance for credit losses summarized on the basis of the Company’s impairment methodology was as follows:
	Commercial,			Real Estate
	Financial,
	Leasing, etc.			Commercial			Residential			Consumer			Total
	(In thousands)
December 31, 2014
Individually evaluated for impairment	$	31,779		$	15,490		$	14,703		$	19,742		$	81,714
Collectively evaluated for impairment		251,607			291,244			45,061			165,140			753,052
Purchased impaired		4,652			1,193			2,146			1,151			9,142
Allocated	$	288,038		$	307,927		$	61,910		$	186,033			843,908
Unallocated														75,654
Total													$	919,562
December 31, 2013
Individually evaluated for impairment	$	24,614		$	27,563		$	21,127		$	18,927		$	92,231
Collectively evaluated for impairment		246,096			296,781			55,864			144,210			742,951
Purchased impaired		2,673			634			1,665			1,507			6,479
Allocated	$	273,383		$	324,978		$	78,656		$	164,644			841,661
Unallocated														75,015
Total													$	916,676
The recorded investment in loans and leases summarized on the basis of the Company’s impairment methodology was as follows:
	Commercial,			Real Estate
	Financial,
	Leasing, etc.			Commercial			Residential			Consumer			Total
	(In thousands)
December 31, 2014
Individually evaluated for impairment	$	206,318		$	252,347		$	232,398		$	69,061		$	760,124
Collectively evaluated for impairment		19,244,674			27,148,382			8,406,680			10,911,359			65,711,095
Purchased impaired		10,300			166,840			18,223			2,374			197,737
Total	$	19,461,292		$	27,567,569		$	8,657,301		$	10,982,794		$	66,668,956
December 31, 2013
Individually evaluated for impairment	$	118,386		$	376,339		$	320,360		$	71,773		$	886,858
Collectively evaluated for impairment		18,571,124			25,488,584			8,578,677			10,217,124			62,855,509
Purchased impaired		15,706			283,285			29,184			2,617			330,792
Total	$	18,705,216		$	26,148,208		$	8,928,221		$	10,291,514		$	64,073,159

Premises_and_equipment

Premises and equipment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Premises and equipment	6.    Premises and equipment
	The detail of premises and equipment was as follows:
		December 31
		2014		2013
		(In thousands)
	Land	$	82,335	$	84,220
	Buildings — owned		406,522		402,065
	Buildings — capital leases		1,131		1,131
	Leasehold improvements		219,152		208,947
	Furniture and equipment — owned		586,429		547,824
	Furniture and equipment — capital leases		18,853		17,703
			1,314,422		1,261,890
	Less: accumulated depreciation and amortization
	Owned assets		686,372		617,228
	Capital leases		15,066		11,142
			701,438		628,370
	Premises and equipment, net	$	612,984	$	633,520
	Net lease expense for all operating leases totaled $104,297,000 in 2014, $103,297,000 in 2013 and $102,924,000 in 2012. Minimum lease payments under noncancelable operating leases are presented in note 21. Minimum lease payments required under capital leases are not material.

Capitalized_servicing_assets

Capitalized servicing assets	12 Months Ended
	Dec. 31, 2014
Transfers and Servicing [Abstract]
Capitalized servicing assets	7.    Capitalized servicing assets
	Changes in capitalized servicing assets were as follows:
		Residential Mortgage Loans									Commercial Mortgage Loans
	For Year Ended December 31,	2014			2013			2012			2014			2013			2012
		(In thousands)
	Beginning balance	$	126,377		$	104,855		$	131,264		$	72,499		$	59,978		$	51,250
	Originations		28,285			52,375			14,577			15,922			26,754			19,653
	Purchases		289			272			109			730			—			—
	Recognized in loan securitization transactions		—			13,696			—			—			—			—
	Amortization		(45,080	)		(44,821	)		(41,095	)		(16,212	)		(14,233	)		(10,925	)
			109,871			126,377			104,855			72,939			72,499			59,978
	Valuation allowance		—			(300	)		(4,500	)		—			—			—
	Ending balance, net	$	109,871		$	126,077		$	100,355		$	72,939		$	72,499		$	59,978
		Other									Total
	For Year Ended December 31,	2014			2013			2012			2014			2013			2012
		(In thousands)
	Beginning balance	$	11,225		$	8,143		$	15,678		$	210,101		$	172,976		$	198,192
	Originations		—			—			—			44,207			79,129			34,230
	Purchases		—			—			—			1,019			272			109
	Recognized in loan securitization transactions		—			9,382			—			—			23,078			—
	Amortization		(7,118	)		(6,300	)		(7,535	)		(68,410	)		(65,354	)		(59,555	)
			4,107			11,225			8,143			186,917			210,101			172,976
	Valuation allowance		—			—			—			—			(300	)		(4,500	)
	Ending balance, net	$	4,107		$	11,225		$	8,143		$	186,917		$	209,801		$	168,476
	Residential mortgage loans serviced for others were $64.4 billion at December 31, 2014, $69.1 billion at December 31, 2013 and $32.1 billion at December 31, 2012. Reflected in residential mortgage loans serviced for others were loans sub-serviced for others of $42.1 billion, $46.6 billion and $12.5 billion at December 31, 2014, 2013, and 2012, respectively. Commercial mortgage loans serviced for others were $11.3 billion at December 31, 2014, $11.4 billion at December 31, 2013 and $10.6 billion at December 31, 2012. Other loans serviced for others include small-balance commercial mortgage loans and automobile loans totaling $3.5 billion, $4.4 billion and $3.8 billion at December 31, 2014, 2013 and 2012, respectively.
	Changes in the valuation allowance for capitalized residential mortgage servicing assets were not significant in 2014, 2013 or 2012. The estimated fair value of capitalized residential mortgage loan servicing assets was approximately $228 million at December 31, 2014 and $266 million at December 31, 2013. The fair value of capitalized residential mortgage loan servicing assets was estimated using weighted-average discount rates of 11.9% and 9.3% at December 31, 2014 and 2013, respectively, and contemporaneous prepayment assumptions that vary by loan type. At December 31, 2014 and 2013, the discount rate represented a weighted-average option-adjusted spread (“OAS”) of 1065 basis points (hundredths of one percent) and 770 basis points, respectively, over market implied forward London Interbank Offered Rates (“LIBOR”). The estimated fair value of capitalized residential mortgage loan servicing rights may vary significantly in subsequent periods due to changing interest rates and the effect thereof on prepayment speeds. The estimated fair value of capitalized commercial mortgage loan servicing assets was approximately $87 million and $85 million at December 31, 2014 and 2013, respectively. An 18% discount rate was used to estimate the fair value of capitalized commercial mortgage loan servicing rights at December 31, 2014 and 2013 with no prepayment assumptions because, in general, the servicing agreements allow the Company to share in customer loan prepayment fees and thereby recover the remaining carrying value of the capitalized servicing rights associated with such loan. The Company’s ability to realize the carrying value of capitalized commercial mortgage servicing rights is more dependent on the borrowers’ abilities to repay the underlying loans than on prepayments or changes in interest rates.
	The key economic assumptions used to determine the fair value of significant portfolios of capitalized servicing rights at December 31, 2014 and the sensitivity of such value to changes in those assumptions are summarized in the table that follows. Those calculated sensitivities are hypothetical and actual changes in the fair value of capitalized servicing rights may differ significantly from the amounts presented herein. The effect of a variation in a particular assumption on the fair value of the servicing rights is calculated without changing any other assumption. In reality, changes in one factor may result in changes in another which may magnify or counteract the sensitivities. The changes in assumptions are presumed to be instantaneous.
		Residential			Commercial
	Weighted-average prepayment speeds		11.22	%
	Impact on fair value of 10% adverse change	$	(8,001,000	)
	Impact on fair value of 20% adverse change		(15,364,000	)
	Weighted-average OAS		10.65	%
	Impact on fair value of 10% adverse change	$	(6,959,000	)
	Impact on fair value of 20% adverse change		(13,492,000	)
	Weighted-average discount rate					18	%
	Impact on fair value of 10% adverse change				$	(3,671,000	)
	Impact on fair value of 20% adverse change					(7,092,000	)
	As described in note 19, during 2013 the Company securitized approximately $1.3 billion of one-to-four family residential mortgage loans formerly held in the Company’s loan portfolio in guaranteed mortgage securitizations with Ginnie Mae and securitized and sold approximately $1.4 billion of automobile loans. In conjunction with these transactions, the Company retained the servicing rights to the loans.

Goodwill_and_other_intangible_

Goodwill and other intangible assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and other intangible assets	8.    Goodwill and other intangible assets
	In accordance with GAAP, the Company does not amortize goodwill, however, core deposit and other intangible assets are amortized over the estimated life of each respective asset. Total amortizing intangible assets were comprised of the following:
		Gross Carrying		Accumulated		Net Carrying
		Amount		Amortization		Amount
		(In thousands)
	December 31, 2014
	Core deposit	$	755,794	$	730,188	$	25,606
	Other		177,268		167,847		9,421
	Total	$	933,062	$	898,035	$	35,027
	December 31, 2013
	Core deposit	$	755,794	$	705,518	$	50,276
	Other		177,268		158,693		18,575
	Total	$	933,062	$	864,211	$	68,851
	Amortization of core deposit and other intangible assets was generally computed using accelerated methods over original amortization periods of five to ten years. The weighted-average original amortization period was approximately eight years. The remaining weighted-average amortization period as of December 31, 2014 was approximately two years. Amortization expense for core deposit and other intangible assets was $33,824,000, $46,912,000 and $60,631,000 for the years ended December 31, 2014, 2013 and 2012, respectively. Estimated amortization expense in future years for such intangible assets is as follows:
		(In thousands)
	Year ending December 31:
	2015	$	20,938
	2016		10,052
	2017		3,303
	2018		734
		$	35,027
	In accordance with GAAP, the Company completed annual goodwill impairment tests as of October 1, 2014, 2013 and 2012. For purposes of testing for impairment, the Company assigned all recorded goodwill to the reporting units originally intended to benefit from past business combinations, which has historically been the Company’s core relationship business reporting units. Goodwill was generally assigned based on the implied fair value of the acquired goodwill applicable to the benefited reporting units at the time of each respective acquisition. The implied fair value of the goodwill was determined as the difference between the estimated incremental overall fair value of the reporting unit and the estimated fair value of the net assets assigned to the reporting unit as of each respective acquisition date. To test for goodwill impairment at each evaluation date, the Company compared the estimated fair value of each of its reporting units to their respective carrying amounts and certain other assets and liabilities assigned to the reporting unit, including goodwill and core deposit and other intangible assets. The methodologies used to estimate fair values of reporting units as of the acquisition dates and as of the evaluation dates were similar. For the Company’s core customer relationship business reporting units, fair value was estimated as the present value of the expected future cash flows of the reporting unit. Based on the results of the goodwill impairment tests, the Company concluded that the amount of recorded goodwill was not impaired at the respective testing dates.
	A summary of goodwill assigned to each of the Company’s reportable segments as of December 31, 2014 and 2013 for purposes of testing for impairment is as follows.
		(In thousands)
	Business Banking	$	748,907
	Commercial Banking		907,524
	Commercial Real Estate		349,197
	Discretionary Portfolio		—
	Residential Mortgage Banking		—
	Retail Banking		1,144,404
	All Other		374,593
	Total	$	3,524,625

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Borrowings	9.    Borrowings
	The amounts and interest rates of short-term borrowings were as follows:
		Federal Funds			Other			Total
		Purchased			Short-term
		and			Borrowings
		Repurchase
		Agreements
		(Dollars in thousands)
	At December 31, 2014
	Amount outstanding	$	192,676			—		$	192,676
	Weighted-average interest rate		0.07	%		—			0.07	%
	For the year ended December 31, 2014
	Highest amount at a month-end	$	280,350			—
	Daily-average amount outstanding		214,736			—		$	214,736
	Weighted-average interest rate		0.05	%		—			0.05	%
	At December 31, 2013
	Amount outstanding	$	260,455			—		$	260,455
	Weighted-average interest rate		0.04	%		—			0.04	%
	For the year ended December 31, 2013
	Highest amount at a month-end	$	563,879			—
	Daily-average amount outstanding		390,034			—		$	390,034
	Weighted-average interest rate		0.11	%		—			0.11	%
	At December 31, 2012
	Amount outstanding	$	1,074,482			—		$	1,074,482
	Weighted-average interest rate		0.11	%		—			0.11	%
	For the year ended December 31, 2012
	Highest amount at a month-end	$	1,224,194		$	50,016
	Daily-average amount outstanding		822,859			16,043		$	838,902
	Weighted-average interest rate		0.15	%		0.57	%		0.15	%
	Short-term borrowings have a stated maturity of one year or less at the date the Company enters into the obligation. In general, federal funds purchased and short-term repurchase agreements outstanding at December 31, 2014 matured on the next business day following year-end.
	At December 31, 2014, the Company had lines of credit under formal agreements as follows:
		M&T Bank			Wilmington
					Trust,  N.A.
		(In thousands)
	Outstanding borrowings	$	1,161,475		$	—
	Unused		19,825,036			275,414
	At December 31, 2014, M&T Bank had borrowing facilities available with the FHLBs whereby M&T Bank could borrow up to approximately $8.1 billion. Additionally, M&T Bank and Wilmington Trust, National Association (“Wilmington Trust, N.A.”), a wholly owned subsidiary of M&T, had available lines of credit with the Federal Reserve Bank of New York totaling approximately $13.1 billion at December 31, 2014. M&T Bank and Wilmington Trust, N.A. are required to pledge loans and investment securities as collateral for these borrowing facilities.
	Long-term borrowings were as follows:
		December 31,
		2014			2013
		(In thousands)
	Senior notes of M&T Bank:
	Variable rate due 2016	$	300,000		$	300,000
	Variable rate due 2017		550,000			—
	1.25% due 2017		499,969			—
	1.40% due 2017		749,756			—
	1.45% due 2018		503,118			502,479
	2.25% due 2019		648,243			—
	2.30% due 2019		748,965			—
	Advances from FHLB:
	Fixed rates		1,161,514			29,079
	Agreements to repurchase securities		1,400,000			1,400,000
	Subordinated notes of Wilmington Trust Corporation
	(a wholly owned subsidiary of M&T):
	8.50% due 2018		218,883			224,067
	Subordinated notes of M&T Bank:
	6.625% due 2017		428,627			437,582
	9.50% due 2018		—			50,000
	5.585% due 2020, variable rate commencing 2015		400,846			392,964
	5.629% due 2021, variable rate commencing 2016		538,961			559,378
	Junior subordinated debentures of M&T associated with preferred capital securities:
	Fixed rates:
	M&T Capital Trust I — 8.234%, due 2027		154,640			154,640
	M&T Capital Trust II — 8.277%, due 2027		103,093			103,093
M&T Capital Trust III — 9.25%, due 2027		65,784			66,109
BSB Capital Trust I — 8.125%, due 2028		15,612			15,589
Provident Trust I — 8.29%, due 2028		25,405			25,051
Southern Financial Statutory Trust I — 10.60%, due 2030		6,550			6,521
M&T Capital Trust IV — 8.50%, due 2068		—			350,010
Variable rates:
First Maryland Capital I — due 2027		145,179			144,641
First Maryland Capital II — due 2027		146,627			145,964
Allfirst Asset Trust — due 2029		96,204			96,059
BSB Capital Trust III — due 2033		15,464			15,464
Provident Trust III — due 2033		52,692			52,176
Southern Financial Capital Trust III — due 2033		7,816			7,747
Other		23,011			30,257
	$	9,006,959		$	5,108,870
During the first quarter of 2013, M&T Bank instituted a Bank Note Program pursuant to which it has issued senior notes in 2014 and 2013. The floating rate notes pay interest quarterly at rates that are indexed to the three-month LIBOR. The contractual interest rates for the floating rate senior notes ranged from 0.54% to 0.61% at December 31, 2014 and were 0.54% at December 31, 2013. The weighted-average contractual interest rate payable was 0.56% at December 31, 2014.
Long-term fixed rate advances from the FHLB had contractual interest rates ranging from 1.17% to 7.32% at December 31, 2014 and from 3.48% to 7.32% at December 31, 2013. The weighted-average contractual interest rates payable were 1.68% at December 31, 2014 and 4.60% at December 31, 2013. Advances from the FHLB mature at various dates through 2035 and are secured by residential real estate loans, commercial real estate loans and investment securities.
Long-term agreements to repurchase securities had contractual interest rates that ranged from 3.61% to 4.30% at each of December 31, 2014 and 2013 with a weighted-average contractual interest rate of 3.90%. The agreements reflect various repurchase dates through 2017, 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 of $1.5 billion and $1.6 billion at December 31, 2014 and 2013, respectively.
The subordinated notes of M&T Bank and Wilmington Trust Corporation are unsecured and are subordinate to the claims of other creditors of those entities.
The fixed and floating rate junior subordinated deferrable interest debentures of M&T (“Junior Subordinated Debentures”) are held by various trusts and 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 current risk-based capital guidelines, the Capital Securities were includable in M&T’s Tier 1 capital through December 31, 2014. In 2015, only 25% of then-outstanding securities are included in Tier 1 capital and beginning in 2016 none of the securities will be included in Tier 1 capital. The variable rate Junior Subordinated Debentures pay interest quarterly at rates that are indexed to the three-month LIBOR. Those rates ranged from 1.08% to 3.58% at December 31, 2014 and from 1.09% to 3.59% at December 31, 2013. The weighted-average variable rates payable on those Junior Subordinated Debentures were 1.66% at December 31, 2014 and 1.67% at December 31, 2013.
Holders of the Capital Securities receive preferential cumulative cash distributions unless M&T exercises its right to extend the payment of interest on the Junior Subordinated Debentures as allowed by the terms of each such debenture, in which case payment of distributions on the respective Capital Securities will be deferred for comparable periods. During an extended interest period, M&T may not pay dividends or distributions on, or repurchase, redeem or acquire any shares of its capital stock. In general, the agreements governing the Capital Securities, in the aggregate, provide a full, irrevocable and unconditional guarantee by M&T of the payment of distributions on, the redemption of, and any liquidation distribution with respect to the Capital Securities. The obligations under such guarantee and the Capital Securities are subordinate and junior in right of payment to all senior indebtedness of M&T.
The Capital Securities will remain outstanding until the Junior Subordinated Debentures are repaid at maturity, are redeemed prior to maturity or are distributed in liquidation to the trusts. The Capital Securities are mandatorily redeemable in whole, but not in part, upon repayment at the stated maturity dates (ranging from 2027 to 2033) of the Junior Subordinated Debentures or the earlier redemption of the Junior Subordinated Debentures in whole upon the occurrence of one or more events set forth in the indentures relating to the Capital Securities, and in whole or in part at any time after an optional redemption prior to contractual maturity contemporaneously with the optional redemption of the related Junior Subordinated Debentures in whole or in part, subject to possible regulatory approval. In February 2014, M&T redeemed all of the issued and outstanding 8.5% $350 million trust preferred securities issued by M&T Capital Trust IV and the related Junior Subordinated Debentures held by M&T Capital Trust IV.
Long-term borrowings at December 31, 2014 mature as follows:
	(In thousands)
Year ending December 31:
2015	$	6,444
2016		1,105,540
2017		3,407,786
2018		723,516
2019		1,971,842
Later years		1,791,831
	$	9,006,959

Shareholders_equity

Shareholders' equity	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Shareholders' equity	10.    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 is presented below:
			December 31, 2014				December 31, 2013
			Shares		Carrying		Shares		Carrying
			Issued and		Value		Issued and		Value
			Outstanding				Outstanding
			(Dollars in thousands)
	Series A(a)
	Fixed Rate Cumulative Perpetual Preferred Stock, Series A, $1,000 liquidation preference per share			230,000	$	230,000		230,000	$	230,000
	Series C(a)
	Fixed Rate Cumulative Perpetual Preferred Stock, Series C, $1,000 liquidation preference per share			151,500		151,500		151,500		151,500
	Series D(b)
	Fixed Rate Non-cumulative Perpetual Preferred Stock, Series D, $10,000 liquidation preference per share			50,000		500,000		50,000		500,000
	Series E(c)
	Fixed-to-Floating Rate Non-cumulative Perpetual Preferred Stock, Series E, $1,000 liquidation preference per share			350,000		350,000		—		—
	(a)	Dividends, if declared, were paid quarterly at a rate of 5% per year through November 14, 2013 and are paid at 6.375% thereafter. Warrants to purchase M&T common stock were issued in connection with the Series A and C preferred stock (Series A — 1,218,522 common shares at $73.86 per share; Series C — 407,542 common shares at $55.76 per share). In March 2013, the Series C warrant were exercised in a “cashless” exercise, resulting in the issuance of 186,589 common shares. During 2014 and 2013, 427,905 and 69,127, respectively, of the Series A warrants were exercised in “cashless” exercises, resulting in the issuance of 169,543 and 25,427 common shares. Remaining outstanding Series A warrants were 721,490 at December 31, 2014.
	(b)	Dividends, if declared, will be paid semi-annually at a rate of 6.875% per year. The shares are redeemable in whole or in part on or after June 15, 2016. 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, will be paid semi-annually at a rate of 6.45% through February 14, 2024 and thereafter will be paid quarterly at a rate of the three-month LIBOR plus 361 basis points (hundredths of one percent). The shares are redeemable in whole or in part on or after February 15, 2024. Notwithstanding M&T’s option to redeem the shares, if an event occurs such that the shares no longer qualify as Tier 1 capital, M&T may redeem all of the shares within 90 days following that occurrence.
	In addition to the Series A and Series C warrants mentioned in (a) above, a ten-year warrant to purchase 95,383 shares of M&T common stock at $518.96 per share was outstanding at each of December 31, 2014 and 2013. The obligation under that warrant was assumed by M&T in an acquisition.

Stockbased_compensation_plans

Stock-based compensation plans	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation plans	11.    Stock-based compensation plans
	Stock-based compensation expense was $65 million in 2014, $55 million in 2013 and $57 million in 2012. The Company recognized income tax benefits related to stock-based compensation of $31 million in 2014, $29 million in 2013 and $30 million in 2012.
	The Company’s equity incentive compensation plan allows for the issuance of various forms of stock-based compensation, including stock options, restricted stock, restricted stock units and performance-based awards. At December 31, 2014 and 2013, respectively, there were 4,398,496 and 4,874,542 shares available for future grant under the Company’s equity incentive compensation plan.
	Restricted stock awards
	Restricted stock awards are comprised of restricted stock and restricted stock units. Restricted stock awards granted in 2014 vest over three years. Restricted stock awards granted prior to 2014 generally vest over four years. A portion of restricted stock awards granted in 2014 require a performance condition to be met before such awards vest. Unrecognized compensation expense associated with restricted stock was $19 million as of December 31, 2014 and is expected to be recognized over a weighted-average period of approximately one year. The Company may issue restricted shares from treasury stock to the extent available or issue new shares. The number of restricted shares issued was 221,822 in 2014, 269,755 in 2013 and 453,908 in 2012, with a weighted-average grant date fair value of $24,765,000 in 2014, $27,716,000 in 2013 and $36,969,000 in 2012. Unrecognized compensation expense associated with restricted stock units was $7 million as of December 31, 2014 and is expected to be recognized over a weighted-average period of approximately one year. During 2014, 2013 and 2012 the number of restricted stock units issued was 299,525, 315,316 and 278,505, respectively, with a weighted-average grant date fair value of $33,406,000, $32,380,000 and $22,139,000, respectively.
	A summary of restricted stock and restricted stock unit activity follows:
		Restricted			Weighted-		Restricted			Weighted-
		Stock Units			Average		Stock			Average
		Outstanding			Grant Price		Outstanding			Grant Price
	Unvested at January 1, 2014		770,830		$	89.58		862,695		$	87.29
	Granted		299,525			111.53		221,822			111.64
	Vested		(279,747	)		84.95		(295,438	)		81.32
	Cancelled		(1,197	)		103.25		(27,434	)		96.7
	Unvested at December 31, 2014		789,411		$	99.53		761,645		$	96.36
	Stock option awards
	Stock options issued generally vest over four years and are exercisable over terms not exceeding ten years and one day. The Company used an option pricing model to estimate the grant date present value of stock options granted. Stock options granted in 2014, 2013 and 2012 were not significant.
	A summary of stock option activity follows:
		Stock			Weighted-Average					Aggregate
		Options								Intrinsic Value
		Outstanding			Exercise		Life			(In thousands)
					Price		(In Years)
	Outstanding at January 1, 2014		4,880,761		$	105.48
	Granted		200			111.51
	Exercised		(1,372,113	)		101.55
	Expired		(75,978	)		184.15
	Outstanding at December 31, 2014		3,432,870		$	105.31		2.1		$	71,418
	Exercisable at December 31, 2014		3,432,470		$	105.31		2.1		$	71,408
	For 2014, 2013 and 2012, M&T received $127 million, $172 million and $153 million, respectively, in cash and realized tax benefits from the exercise of stock options of $9 million, $12 million and $8 million, respectively. The intrinsic value of stock options exercised during those periods was $26 million, $34 million and $21 million, respectively. As of December 31, 2014, the amount of unrecognized compensation cost related to non-vested stock options was not significant. The total grant date fair value of stock options vested during 2014 and 2013 was not significant, and for 2012 was $17 million. Upon the exercise of stock options, the Company may issue shares from treasury stock to the extent available or issue new shares.
	Stock purchase plan
	The stock purchase plan provides eligible employees of the Company with the right to purchase shares of M&T common stock at a discount through accumulated payroll deductions. In connection with the employee stock purchase plan, 2,500,000 shares of M&T common stock were authorized for issuance under a plan adopted in 2013. There were 85,761 shares issued in 2014, no shares issued in 2013 and 151,014 shares issued in 2012 under a previous plan. For 2014 and 2012, M&T received $8,607,000 and $10,117,000, respectively, in cash for shares purchased through the employee stock purchase plan. Compensation expense recognized for the stock purchase plan was not significant in 2014, 2013 or 2012.
	Deferred bonus plan
	The Company provided a deferred bonus plan pursuant to which eligible employees could elect to defer all or a portion of their annual incentive compensation awards and allocate such awards to several investment options, including M&T common stock. Participants could elect the timing of distributions from the plan. Such distributions are payable in cash with the exception of balances allocated to M&T common stock which are distributable in the form of M&T common stock. Shares of M&T common stock distributable pursuant to the terms of the deferred bonus plan were 29,297 and 33,046 at December 31, 2014 and 2013, respectively. The obligation to issue shares is included in “common stock issuable” in the consolidated balance sheet.
	Directors’ stock plan
	The Company maintains a compensation plan for non-employee members of the Company’s boards of directors and directors advisory councils that allows such members to receive all or a portion of their compensation in shares of M&T common stock. Through December 31, 2014, 211,655 shares had been issued in connection with the directors’ stock plan.
	Through acquisitions, the Company assumed obligations to issue shares of M&T common stock related to deferred directors compensation plans. Shares of common stock issuable under such plans were 12,033 and 14,185 at December 31, 2014 and 2013, respectively. The obligation to issue shares is included in “common stock issuable” in the consolidated balance sheet.

Pension_plans_and_other_postre

Pension plans and other postretirement benefits	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Pension plans and other postretirement benefits	12.    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. The Company uses a December 31 measurement date for all of its plans.
	Net periodic pension expense for defined benefit plans consisted of the following:
			Year Ended December 31
			2014			2013			2012
			(In thousands)
	Service cost		$	20,520		$	24,360		$	29,549
	Interest cost on benefit obligation			69,162			60,130			62,037
	Expected return on plan assets			(91,568	)		(87,353	)		(70,511	)
	Amortization of prior service credit			(6,552	)		(6,556	)		(6,559	)
	Recognized net actuarial loss			14,494			41,076			37,386
	Net periodic pension expense		$	6,056		$	31,657		$	51,902
	Net other postretirement benefits expense for defined benefit plans consisted of the following:
			Year Ended December 31
			2014			2013			2012
			(In thousands)
	Service cost		$	605		$	742		$	668
	Interest cost on benefit obligation			2,778			2,691			3,737
	Amortization of prior service cost (credit)			(1,359	)		(1,359	)		21
	Recognized net actuarial loss			—			360			530
	Net other postretirement benefits expense		$	2,024		$	2,434		$	4,956
	Data relating to the funding position of the defined benefit plans were as follows:
			Pension Benefits						Other
									Postretirement Benefits
			2014			2013			2014			2013
			(In thousands)
	Change in benefit obligation:
	Benefit obligation at beginning of year		$	1,484,193		$	1,644,567		$	60,592		$	74,966
	Service cost			20,520			24,360			605			742
	Interest cost			69,162			60,130			2,778			2,691
	Plan participants’ contributions			—			—			3,498			3,069
	Amendments			4,619			—			—			—
	Actuarial (gain) loss			300,444			(184,181	)		7,793			(12,830	)
	Medicare Part D reimbursement			—			—			495			509
	Benefits paid			(65,529	)		(60,683	)		(8,259	)		(8,555	)
	Benefit obligation at end of year			1,813,409			1,484,193			67,502			60,592
	Change in plan assets:
	Fair value of plan assets at beginning of year			1,506,684			1,408,771			—			—
	Actual return on plan assets			56,430			150,795			—			—
	Employer contributions			8,076			7,801			4,266			4,977
	Plan participants’ contributions			—			—			3,498			3,069
	Medicare Part D reimbursement			—			—			495			509
	Benefits and other payments			(65,529	)		(60,683	)		(8,259	)		(8,555	)
	Fair value of plan assets at end of year			1,505,661			1,506,684			—			—
	Funded status		$	(307,748	)	$	22,491		$	(67,502	)	$	(60,592	)
	Assets and liabilities recognized in the consolidated balance sheet were:
	Net prepaid asset		$	—		$	139,576		$	—		$	—
	Accrued liabilities			(307,748	)		(117,085	)		(67,502	)		(60,592	)
	Amounts recognized in accumulated other comprehensive income (“AOCI”) were:
	Net loss (gain)		$	512,473		$	191,386		$	6,737		$	(1,056	)
	Net prior service cost			(5,728	)		(16,899	)		(10,455	)		(11,814	)
	Pre-tax adjustment to AOCI			506,745			174,487			(3,718	)		(12,870	)
	Taxes.			(198,897	)		(68,486	)		1,459			5,051
	Net adjustment to AOCI.		$	307,848		$	106,001		$	(2,259	)	$	(7,819	)
	The Company has an unfunded supplemental pension plan for certain key executives and others. The projected benefit obligation and accumulated benefit obligation included in the preceding data related to such plan were $135,891,000 as of December 31, 2014 and $117,085,000 as of December 31, 2013.
	The accumulated benefit obligation for all defined benefit pension plans was $1,782,387,000 and $1,460,498,000 at December 31, 2014 and 2013, respectively.
	GAAP requires an employer to recognize in its balance sheet as an asset or liability the overfunded or underfunded status of a defined benefit postretirement plan, measured as the difference between the fair value of plan assets and the benefit obligation. For a pension plan, the benefit obligation is the projected benefit obligation; for any other postretirement benefit plan, such as a retiree health care plan, the benefit obligation is the accumulated postretirement benefit obligation. Gains or losses and prior service costs or credits that arise during the period, but are not included as components of net periodic benefit expense, are recognized as a component of other comprehensive income. As indicated in the preceding table, as of December 31, 2014 the Company recorded a minimum liability adjustment of $503,027,000 ($506,745,000 related to pension plans and $(3,718,000) related to other postretirement benefits) with a corresponding reduction of shareholders’ equity, net of applicable deferred taxes, of $305,589,000. In aggregate, the benefit plans realized a net loss during 2014 that resulted from actual experience differing from the plan assumptions utilized and from changes in actuarial assumptions. The main factors contributing to that loss were a decrease in the discount rate used in the measurement of the benefit obligations to 4.00% at December 31, 2014 from 4.75% at December 31, 2013 and the migration to updated actuarial mortality tables issued by the Society of Actuaries reflecting longer life expectancy of the plan’s participants. As a result, the Company increased its minimum liability adjustment from that which was recorded at December 31, 2013 by $341,410,000 with a corresponding decrease to shareholders’ equity that, net of applicable deferred taxes, was $207,407,000. The table below reflects the changes in plan assets and benefit obligations recognized in other comprehensive income related to the Company’s postretirement benefit plans.
			Pension Plans			Other			Total
						Postretirement
						Benefit Plans
			(In thousands)
	2014
	Net loss		$	335,581		$	7,793		$	343,374
	Prior service cost			4,619			—			4,619
Amortization of prior service credit			6,552			1,359			7,911
Amortization of loss			(14,494	)		—			(14,494	)
Total recognized in other comprehensive income, pre-tax		$	332,258		$	9,152		$	341,410
2013
Net gain		$	(247,622	)	$	(12,830	)	$	(260,452	)
Amortization of prior service credit			6,556			1,359			7,915
Amortization of loss			(41,076	)		(360	)		(41,436	)
Total recognized in other comprehensive income, pre-tax		$	(282,142	)	$	(11,831	)	$	(293,973	)
The following table reflects the amortization of amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit expense during 2015:
		Pension Plans			Other
					Postretirement
					Benefit Plans
		(In thousands)
Amortization of net prior service credit		$	(6,005	)	$	(1,359	)
Amortization of net loss			44,653			91
The Company also provides a qualified defined contribution pension plan to eligible employees who were not participants in the defined benefit pension plan as of December 31, 2005 and to other employees who have elected to participate in the defined contribution plan. The Company makes contributions to the defined contribution plan each year in an amount that is based on an individual participant’s total compensation (generally defined as total wages, incentive compensation, commissions and bonuses) and years of service. Participants do not contribute to the defined contribution pension plan. Pension expense recorded in 2014, 2013 and 2012 associated with the defined contribution pension plan was approximately $22 million, $21 million and $17 million, respectively.
Assumptions
The assumed weighted-average rates used to determine benefit obligations at December 31 were:
		Pension						Other
		Benefits						Postretirement
								Benefits
		2014			2013			2014			2013
Discount rate			4	%		4.75	%		4	%		4.75	%
Rate of increase in future compensation levels			4.39	%		4.42	%		—			—
The assumed weighted-average rates used to determine net benefit expense for the years ended December 31 were:
		Pension Benefits									Other
											Postretirement Benefits
		2014			2013			2012			2014			2013			2012
Discount rate			4.75	%		3.75	%		4.25	%		4.75	%		3.75	%		4.25	%
Long-term rate of return on plan assets			6.5	%		6.5	%		6.5	%		—			—			—
Rate of increase in future compensation levels			4.42	%		4.5	%		4.5	%		—			—			—
The expected long-term rate of return assumption as of each measurement date was developed through analysis of historical market returns, current market conditions, anticipated future asset allocations, the funds’ past experience, and expectations on potential future market returns. The expected rate of return assumption represents a long-term average view of the performance of the plan assets, a return that may or may not be achieved during any one calendar year.
For measurement of other postretirement benefits, a 7.00% annual rate of increase in the per capita cost of covered health care benefits was assumed for 2015. The rate was assumed to decrease to 5.00% over 28 years. A one-percentage point change in assumed health care cost trend rates would have had the following effects:
		1%			-1%
		(In thousands)
Increase (decrease) in:
Service and interest cost		$	97		$	(88	)
Accumulated postretirement benefit obligation			3,005			(2,678	)
Plan Assets
The Company’s policy is to invest the pension plan assets in a prudent manner for the purpose of providing benefit payments to participants and mitigating reasonable expenses of administration. The Company’s investment strategy is designed to provide a total return that, over the long-term, places a strong emphasis on the preservation of capital. The strategy attempts to maximize investment returns on assets at a level of risk deemed appropriate by the Company while complying with applicable regulations and laws. The investment strategy utilizes asset diversification as a principal determinant for establishing an appropriate risk profile while emphasizing total return realized from capital appreciation, dividends and interest income. The target allocations for plan assets are generally 45 to 80 percent equity securities, 5 to 40 percent debt securities, and 5 to 30 percent money-market funds/cash equivalents and other investments, although holdings could be more or less than these general guidelines based on market conditions at the time and actions taken or recommended by the investment managers providing advice to the Company. Equity securities include investments in large-cap and mid-cap companies located in the United States and equity mutual funds with domestic and international investments, and, to a lesser extent, direct investments in foreign-based companies. Debt securities include corporate bonds of companies from diversified industries, mortgage-backed securities guaranteed by government agencies, U.S. Treasury securities, and mutual funds that invest in debt securities. Additionally, the Company’s defined benefit pension plan held $172,026,000 (11.4% of total assets) of real estate, private equity and other investments at December 31, 2014. Returns on invested assets are periodically compared with target market indices for each asset type to aid management in evaluating such returns. Furthermore, management regularly reviews the investment policy and may, if deemed appropriate, make changes to the target allocations noted above.
The fair values of the Company’s pension plan assets at December 31, 2014, by asset category, were as follows:
		Fair Value Measurement of Plan Assets At December 31, 2014
		Total			Quoted Prices			Significant			Significant
					in Active			Observable			Unobservable
					Markets			Inputs			Inputs
					for Identical Assets			(Level 2)			(Level 3)
					(Level 1)
		(In thousands)
Asset category:
Money-market funds		$	29,458		$	29,458		$	—		$	—
Equity securities:
M&T			154,252			154,252			—			—
Domestic(a)			214,127			214,127			—			—
International(b)			16,170			16,170			—			—
Mutual funds:
Domestic(a)			305,817			305,817			—			—
International(b)			381,101			381,101			—			—
			1,071,467			1,071,467			—			—
Debt securities:
Corporate(c)			102,848			—			102,848			—
Government			92,772			—			92,772			—
International			7,196			—			7,196			—
Mutual funds:
Domestic(d)			27,847			27,847			—			—
			230,663			27,847			202,816			—
Other:
Diversified mutual fund			96,936			96,936			—			—
Private real estate			2,162			—			—			2,162
Private equity			6,234			—			—			6,234
Hedge funds			66,694			42,430			—			24,264
			172,026			139,366			—			32,660
Total(e)		$	1,503,614		$	1,268,138		$	202,816		$	32,660
The fair values of the Company’s pension plan assets at December 31, 2013, by asset category, were as follows:
		Fair Value Measurement of Plan Assets At December 31, 2013
		Total			Quoted Prices			Significant			Significant
					in Active			Observable			Unobservable
					Markets			Inputs			Inputs
					for Identical Assets			(Level 2)			(Level 3)
					(Level 1)
		(In thousands)
Asset category:
Money-market funds		$	37,952		$	37,952		$	—		$	—
Equity securities:
M&T			142,955			142,955			—			—
Domestic(a)			271,203			271,203			—			—
International(b)			24,053			24,053			—			—
Mutual funds:
Domestic(a)			194,099			194,099			—			—
International(b)			413,685			413,685			—			—
			1,045,995			1,045,995			—			—
Debt securities:
Corporate(c)			63,196			—			63,196			—
Government			75,043			—			75,043			—
International			2,443			—			2,443			—
Mutual funds:
Domestic(d)			68,280			68,280			—			—
International			43,742			43,742			—			—
			252,704			112,022			140,682			—
Other:
Diversified mutual fund			93,055			93,055			—			—
Private real estate			3,123			—			—			3,123
Private equity			6,199			—			—			6,199
Hedge funds			65,663			41,489			—			24,174
			168,040			134,544			—			33,496
Total(e)		$	1,504,691		$	1,330,513		$	140,682		$	33,496
(a)	This category is comprised of equities of companies primarily within the mid-cap and large-cap sectors of the U.S. economy and range across diverse industries.
(b)	This category is comprised of equities in companies primarily within the mid-cap and large-cap sectors of international markets mainly in developed markets in Europe and the Pacific Rim.
(c)	This category represents investment grade bonds of U.S. issuers from diverse industries.
(d)	Approximately 55% of the mutual funds were invested in investment grade bonds of U.S. issuers and 45% in high-yielding bonds at December 31, 2014. Approximately 35% of the mutual funds were invested in investment grade bonds of U.S. issuers and 65% in high-yielding bonds at December 31, 2013. The holdings within the funds were spread across diverse industries.
(e)	Excludes dividends and interest receivable totaling $2,047,000 and $1,993,000 at December 31, 2014 and 2013, respectively.
Pension plan assets included common stock of M&T with a fair value of $154,252,000 (10.2% of total plan assets) at December 31, 2014 and $142,955,000 (9.5% of total plan assets) at December 31, 2013. No other investment in securities of a non-U.S. Government or government agency issuer exceeded ten percent of plan assets at December 31, 2014. Assets subject to Level 3 valuations did not constitute a significant portion of plan assets at December 31, 2014 or December 31, 2013.
The changes in Level 3 pension plan assets measured at estimated fair value on a recurring basis during the year ended December 31, 2014 were as follows:
		Balance –			Sales			Total			Balance –
		January 1,						Realized/			December 31,
		2014						Unrealized			2014
								Gains
		(In thousands)
Other
Private real estate		$	3,123		$	(1,167	)	$	206		$	2,162
Private equity			6,199			(905	)		940			6,234
Hedge funds			24,174			(513	)		603			24,264
Total		$	33,496		$	(2,585	)	$	1,749		$	32,660
The Company makes contributions to its funded qualified defined benefit pension plan as required by government regulation or as deemed appropriate by management after considering factors such as the fair value of plan assets, expected returns on such assets, and the present value of benefit obligations of the plan. Subject to the impact of actual events and circumstances that may occur in 2015, the Company may make contributions to the qualified defined benefit pension plan in 2015, but the amount of any such contribution has not yet been determined. The Company did not make any contributions to the plan in 2014 or 2013. The Company regularly funds the payment of benefit obligations for the supplemental defined benefit pension and postretirement benefit plans because such plans do not hold assets for investment. Payments made by the Company for supplemental pension benefits were $8,076,000 and $7,801,000 in 2014 and 2013, respectively. Payments made by the Company for postretirement benefits were $4,266,000 and $4,977,000 in 2014 and 2013, respectively. Payments for supplemental pension and other postretirement benefits for 2015 are not expected to differ from those made in 2014 by an amount that will be material to the Company’s consolidated financial position.
Estimated benefits expected to be paid in future years related to the Company’s defined benefit pension and other postretirement benefits plans are as follows:
		Pension			Other
		Benefits			Postretirement
					Benefits
		(In thousands)
Year ending December 31:
2015		$	70,107		$	5,830
2016			73,169			5,719
2017			77,294			5,554
2018			81,231			5,412
2019			87,027			5,281
2020 through 2024			497,177			24,190
The Company has a retirement savings plan (“RSP”) that is a defined contribution plan in which eligible employees of the Company may defer up to 50% of qualified compensation via contributions to the plan. The Company makes an employer matching contribution in an amount equal to 75% of an employee’s contribution, up to 4.5% of the employee’s qualified compensation. Employees’ accounts, including employee contributions, employer matching contributions and accumulated earnings thereon, are at all times fully vested and nonforfeitable. Employee benefits expense resulting from the Company’s contributions to the RSP totaled $32,466,000, $31,797,000 and $31,305,000 in 2014, 2013 and 2012, respectively.

Income_taxes

Income taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income taxes	13.    Income taxes
	The components of income tax expense were as follows:
		Year Ended December 31
		2014			2013			2012
		(In thousands)
	Current
	Federal	$	378,978		$	371,249		$	309,156
	State and city		50,790			68,035			82,014
	Total current		429,768			439,284			391,170
	Deferred
	Federal		65,503			106,537			117,229
	State and city		27,345			33,248			14,629
	Total deferred		92,848			139,785			131,858
	Total income taxes applicable to pre-tax income	$	522,616		$	579,069		$	523,028
	The Company files a consolidated federal income tax return reflecting taxable income earned by all domestic subsidiaries. In prior years, applicable federal tax law allowed certain financial institutions the option of deducting as bad debt expense for tax purposes amounts in excess of actual losses. In accordance with GAAP, such financial institutions were not required to provide deferred income taxes on such excess. Recapture of the excess tax bad debt reserve established under the previously allowed method will result in taxable income if M&T Bank fails to maintain bank status as defined in the Internal Revenue Code or charges are made to the reserve for other than bad debt losses. At December 31, 2014, M&T Bank’s tax bad debt reserve for which no federal income taxes have been provided was $79,121,000. No actions are planned that would cause this reserve to become wholly or partially taxable.
	Income taxes attributable to gains or losses on bank investment securities were an expense of $18,313,000 in 2013 and a benefit of $18,766,000 in 2012. There were no gains or losses on bank investment securities in 2014. No alternative minimum tax expense was recognized in 2014, 2013 or 2012.
	Total income taxes differed from the amount computed by applying the statutory federal income tax rate to pre-tax income as follows:
		Year Ended December 31
		2014			2013			2012
		(In thousands)
	Income taxes at statutory federal income tax rate	$	556,102		$	601,142		$	543,384
	Increase (decrease) in taxes:
	Tax-exempt income		(31,752	)		(34,747	)		(33,890	)
	State and city income taxes, net of federal income tax effect		50,788			65,834			62,818
	Low income housing and other credits		(49,526	)		(49,206	)		(42,074	)
	Other		(2,996	)		(3,954	)		(7,210	)
		$	522,616		$	579,069		$	523,028
	Deferred tax assets (liabilities) were comprised of the following at December 31:
		2014			2013			2012
		(In thousands)
	Losses on loans and other assets	$	605,273		$	645,713		$	809,033
	Postretirement and other employee benefits		34,052			30,023			34,517
	Incentive compensation plans		36,450			37,772			50,067
	Interest on loans		79,147			100,725			72,278
	Retirement benefits		120,222			—			91,980
	Stock-based compensation		64,017			63,101			69,874
	Depreciation and amortization		3,527			1,404			12,130
	Other		100,999			121,561			103,027
	Gross deferred tax assets		1,043,687			1,000,299			1,242,906
	Leasing transactions		(280,596	)		(284,370	)		(291,524	)
	Unrealized investment gains		(82,065	)		(21,779	)		(23,574	)
	Capitalized servicing rights		(46,393	)		(46,041	)		(20,348	)
	Interest on subordinated note exchange		(3,125	)		(6,075	)		(8,794	)
	Retirement benefits		—			(9,397	)		—
	Other		(63,814	)		(49,450	)		(61,410	)
	Gross deferred tax liabilities		(475,993	)		(417,112	)		(405,650	)
	Net deferred tax asset	$	567,694		$	583,187		$	837,256
	The Company believes that it is more likely than not that the deferred tax assets will be realized through taxable earnings or alternative tax strategies.
	The income tax credits shown in the statement of income of M&T in note 25 arise principally from operating losses before dividends from subsidiaries.
	A reconciliation of the beginning and ending amount of unrecognized tax benefits follows:
		Federal,			Accrued			Unrecognized
		State and			Interest			Income Tax
		Local Tax						Benefits
		(In thousands)
	Gross unrecognized tax benefits at January 1, 2012	$	18,333		$	9,277		$	27,610
	Increases in unrecognized tax benefits as a result of tax positions taken during 2012		860			—			860
	Increases in unrecognized tax benefits as a result of tax positions taken in prior years		—			4,514			4,514
	Decreases in unrecognized tax benefits as a result of settlements with taxing authorities		(1,002	)		—			(1,002	)
	Decreases in unrecognized tax benefits because applicable returns are no longer subject to examination		(1,643	)		(1,412	)		(3,055	)
	Gross unrecognized tax benefits at December 31, 2012		16,548			12,379			28,927
	Increases in unrecognized tax benefits as a result of tax positions taken during 2013		2,267			—			2,267
	Increases in unrecognized tax benefits as a result of tax positions taken in prior years		—			4,429			4,429
	Decreases in unrecognized tax benefits as a result of settlements with taxing authorities		(1,854	)		(487	)		(2,341	)
	Decreases in unrecognized tax benefits because applicable returns are no longer subject to examination		(2,350	)		(1,625	)		(3,975	)
Gross unrecognized tax benefits at December 31, 2013		14,611			14,696			29,307
Increases in unrecognized tax benefits as a result of tax positions taken during 2014		769			—			769
Increases in unrecognized tax benefits as a result of tax positions taken in prior years		—			453			453
Decreases in unrecognized tax benefits as a result of settlements with taxing authorities		(4,668	)		(11,280	)		(15,948	)
Gross unrecognized tax benefits at December 31, 2014	$	10,712		$	3,869			14,581
Less: Federal, state and local income tax benefits								(5,103	)
Net unrecognized tax benefits at December 31, 2014 that, if recognized, would impact the effective income tax rate							$	9,478
The Company’s policy is to recognize interest and penalties, if any, related to unrecognized tax benefits in income taxes in the consolidated statement of income. The balance of accrued interest at December 31, 2014 is included in the table above. The Company’s federal, state and local income tax returns are routinely subject to examinations from various governmental taxing authorities. Such examinations may result in challenges to the tax return treatment applied by the Company to specific transactions. Management believes that the assumptions and judgment used to record tax-related assets or liabilities have been appropriate. Should determinations rendered by tax authorities ultimately indicate that management’s assumptions were inappropriate, the result and adjustments required could have a material effect on the Company’s results of operations. Under statute, the Company’s federal income tax returns for the years 2010 through 2013 could be adjusted by the Internal Revenue Service, although examinations for those tax years have been largely concluded. The Company also files income tax returns in over forty states and numerous local jurisdictions. Substantially all material state and local matters have been concluded for years through 2010. It is not reasonably possible to estimate when examinations for any subsequent years will be completed.

Earnings_per_common_share

Earnings per common share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Earnings per common share	14.    Earnings per common share
	The computations of basic earnings per common share follow:
			Year Ended December 31
			2014			2013			2012
			(In thousands, except per share)
	Income available to common shareholders:
	Net income		$	1,066,246		$	1,138,480		$	1,029,498
	Less: Preferred stock dividends(a)			(75,878	)		(54,120	)		(53,450	)
	Amortization of preferred stock discount(a)			—			(7,942	)		(8,026	)
	Net income available to common equity			990,368			1,076,418			968,022
	Less: Income attributable to unvested stock-based compensation awards			(11,837	)		(13,989	)		(14,632	)
	Net income available to common shareholders		$	978,531		$	1,062,429		$	953,390
	Weighted-average shares outstanding:
	Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards			132,532			130,354			127,793
	Less: Unvested stock-based compensation awards			(1,582	)		(1,700	)		(1,929	)
	Weighted-average shares outstanding			130,950			128,654			125,864
	Basic earnings per common share		$	7.47		$	8.26		$	7.57
	(a)	Including impact of not as yet declared cumulative dividends.
	The computations of diluted earnings per common share follow:
			Year Ended December 31
			2014			2013			2012
			(In thousands, except per share)
	Net income available to common equity		$	990,368		$	1,076,418		$	968,022
	Less: Income attributable to unvested stock-based compensation awards			(11,787	)		(13,922	)		(14,593	)
	Net income available to common shareholders		$	978,581		$	1,062,496		$	953,429
	Adjusted weighted-average shares outstanding:
	Common and unvested stock-based compensation awards			132,532			130,354			127,793
	Less: Unvested stock-based compensation awards			(1,582	)		(1,700	)		(1,929	)
	Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock			894			949			541
	Adjusted weighted-average shares outstanding			131,844			129,603			126,405
	Diluted earnings per common share		$	7.42		$	8.2		$	7.54
	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 approximately 2,017,000, 3,847,000 and 8,905,000 common shares during 2014, 2013 and 2012, respectively, were not included in the computations of diluted earnings per common share because the effect on those years would have been antidilutive.

Comprehensive_income

Comprehensive income	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Comprehensive income	15.    Comprehensive income
	The following tables display the components of other comprehensive income (loss) and amounts reclassified from accumulated other comprehensive income (loss) to net income.
			Investment Securities						Defined			Other			Total			Income			Net
									Benefit						Amount			Tax
			With			All			Plans						Before Tax
			OTTI			Other
			(In thousands)
	Balance — January 1, 2014		$	37,255			18,450			(161,617	)		115			(105,797	)		41,638		$	(64,159	)
	Other comprehensive income before reclassifications:
	Unrealized holding gains (losses), net			(29,818	)		180,005			—			—			150,187			(58,962	)		91,225
	Foreign currency translation adjustment			—			—			—			(4,039	)		(4,039	)		1,432			(2,607	)
	Unrealized losses on cash flow hedges			—			—			—			(165	)		(165	)		65			(100	)
	Current year benefit plans losses			—			—			(347,993	)		—			(347,993	)		136,587			(211,406	)
	Total other comprehensive income (loss) before reclassifications			(29,818	)		180,005			(347,993	)		(4,204	)		(202,010	)		79,122			(122,888	)
	Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
	Accretion of unrealized holding losses on held-to-maturity (“HTM”) securities			1			3,373			—			—			3,374	(a)		(1,324	)		2,050
	Accretion of losses on terminated cash flow hedges			—			—			—			7			7	(d)		(3	)		4
	Amortization of prior service credit			—			—			(7,911	)		—			(7,911	)(e)		3,105			(4,806	)
	Amortization of actuarial losses			—			—			14,494			—			14,494	(e)		(5,689	)		8,805
	Total reclassifications			1			3,373			6,583			7			9,964			(3,911	)		6,053
	Total gain (loss) during the period			(29,817	)		183,378			(341,410	)		(4,197	)		(192,046	)		75,211			(116,835	)
	Balance — December 31, 2014		$	7,438			201,828			(503,027	)		(4,082	)		(297,843	)		116,849		$	(180,994	)
			Investment Securities						Defined			Other			Total			Income			Net
									Benefit						Amount			Tax
			With			All			Plans						Before Tax
			OTTI			Other
			(In thousands)
	Balance — January 1, 2013		$	(91,835	)		152,199			(455,590	)		(431	)		(395,657	)		155,393		$	(240,264	)
	Other comprehensive income before reclassifications:
	Unrealized holding gains (losses), net			77,794			(129,628	)		—			—			(51,834	)		20,311			(31,523	)
	Foreign currency translation adjustment			—			—			—			546			546			(165	)		381
	Current year benefit plans gains			—			—			260,452			—			260,452			(102,227	)		158,225
	Total other comprehensive income (loss) before reclassifications			77,794			(129,628	)		260,452			546			209,164			(82,081	)		127,083
	Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
	Accretion of unrealized holding losses on HTM securities			279			4,008			—			—			4,287	(a)		(1,683	)		2,604
	OTTI charges recognized in net income			9,800			—			—			—			9,800	(b)		(3,847	)		5,953
	Losses (gains) realized in net income			41,217			(8,129	)		—			—			33,088	(c)		(12,987	)		20,101
	Amortization of prior service credit			—			—			(7,915	)		—			(7,915	)(e)		3,107			(4,808	)
	Amortization of actuarial losses			—			—			41,436			—			41,436	(e)		(16,264	)		25,172
	Total reclassifications			51,296			(4,121	)		33,521			—			80,696			(31,674	)		49,022
	Total gain (loss) during the period			129,090			(133,749	)		293,973			546			289,860			(113,755	)		176,105
	Balance —December 31, 2013		$	37,255			18,450			(161,617	)		115			(105,797	)		41,638		$	(64,159	)
			Investment Securities						Defined			Other			Total			Income			Net
									Benefit						Amount			Tax
			With			All			Plans						Before Tax
			OTTI			Other
			(In thousands)
	Balance — January 1, 2012		$	(138,319	)		9,757			(457,145	)		(1,062	)		(586,769	)		230,328		$	(356,441	)
	Other comprehensive income before reclassifications:
	Unrealized holding gains (losses), net			(2,998	)		137,921			—			—			134,923			(52,905	)		82,018
	Foreign currency translation adjustment			—			—			—			809			809			(290	)		519
	Current year benefit plans losses			—			—			(29,823	)		—			(29,823	)		11,705			(18,118	)
	Total other comprehensive income (loss) before reclassifications			(2,998	)		137,921			(29,823	)		809			105,909			(41,490	)		64,419
	Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
	Accretion of unrealized holding losses on HTM securities			1,660			4,530			—			—			6,190	(a)		(2,430	)		3,760
	OTTI charges recognized in net income			47,822			—			—			—			47,822	(b)		(18,770	)		29,052
	Gains realized in net income			—			(9	)		—			—			(9	)(c)		4			(5	)
	Amortization of gains on terminated cash flow hedges			—			—			—			(178	)		(178	)(d)		66			(112	)
	Amortization of prior service credit			—			—			(6,538	)		—			(6,538	)(e)		2,566			(3,972	)
	Amortization of actuarial losses			—			—			37,916			—			37,916	(e)		(14,881	)		23,035
	Total reclassifications			49,482			4,521			31,378			(178	)		85,203			(33,445	)		51,758
	Total gain during the period			46,484			142,442			1,555			631			191,112			(74,935	)		116,177
	Balance —December 31, 2012		$	(91,835	)		152,199			(455,590	)		(431	)		(395,657	)		155,393		$	(240,264	)
	(a)	Included in interest income.
(b)	Included in OTTI losses recognized in earnings.
(c)	Included in gain (loss) on bank investment securities.
(d)	Included in interest expense.
(e)	Included in salaries and employee benefits expense.
Accumulated other comprehensive income (loss), net consisted of unrealized gains (losses) as follows:
		Investment Securities						Defined			Other			Total
								Benefit
		With OTTI			All Other			Plans
								(In thousands)
Balance at January 1, 2012		$	(84,029	)	$	5,995		$	(277,716	)	$	(691	)	$	(356,441	)
Net gain (loss) during 2012			28,239			86,586			945			407			116,177
Balance at December 31, 2012			(55,790	)		92,581			(276,771	)		(284	)		(240,264	)
Net gain (loss) during 2013			78,422			(81,287	)		178,589			381			176,105
Balance at December 31, 2013			22,632			11,294			(98,182	)		97			(64,159	)
Net gain (loss) during 2014			(18,114	)		111,389			(207,407	)		(2,703	)		(116,835	)
Balance at December 31, 2014		$	4,518		$	122,683		$	(305,589	)	$	(2,606	)	$	(180,994	)

Other_income_and_other_expense

Other income and other expense	12 Months Ended
	Dec. 31, 2014
Other Income and Expenses [Abstract]
Other income and other expense	16.    Other income and other expense
	The following items, which exceeded 1% of total interest income and other income in the respective period, were included in either “other revenues from operations” or “other costs of operations” in the consolidated statement of income:
		Year Ended December 31
		2014		2013		2012
		(In thousands)
	Other income:
	Bank owned life insurance	$	50,004	$	56,120	$	51,199
	Credit-related fee income		72,454		72,271		68,596
	Letter of credit fees		56,708		59,889		58,496
	Gains from loan securitization transactions				63,066
	Other expense:
	Professional services		401,946		335,794		248,544
	Amortization of capitalized servicing rights		68,410		65,354		59,555
	Advertising and promotion				56,597		52,388

International_activities

International activities	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
International activities	17.    International activities
	The Company engages in limited international activities including certain trust-related services in Europe and the Cayman Islands, collecting Eurodollar deposits, engaging in foreign currency trading on behalf of customers, providing credit to support the international activities of domestic companies and holding certain loans to foreign borrowers. Revenues from providing international trust-related services were approximately $31 million in 2014, $26 million in 2013 and $24 million in 2012. Net assets identified with international activities amounted to $232 million and $226 million at December 31, 2014 and 2013, respectively. Such assets included $213 million and $192 million, respectively, of loans to foreign borrowers. Deposits at M&T Bank’s Cayman Islands office were $177 million and $323 million at December 31, 2014 and 2013, respectively. The Company uses such deposits to facilitate customer demand and as an alternative to short-term borrowings when the costs of such deposits seem reasonable.

Derivative_financial_instrumen

Derivative financial instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative financial instruments	18.    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 and collateral provisions protecting the at-risk party. Based on adherence to the Company’s credit standards and the presence of the netting and collateral provisions, the Company believes that the credit risk inherent in these contracts was not significant as of December 31, 2014.
	The net effect of interest rate swap agreements was to increase net interest income by $45 million in 2014, $41 million in 2013 and $36 million in 2012. The average notional amounts of interest rate swap agreements impacting net interest income that were entered into for interest rate risk management purposes were $1.4 billion in 2014, $1.2 billion in 2013 and $900 million in 2012.
	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						Estimated Fair
			Amount			Maturity		Rate						Value Gain
								Fixed			Variable
			(In thousands)			(In years)								(In thousands)
	December 31, 2014
	Fair value hedges:
	Fixed rate long-term borrowings(a)		$	1,400,000			2.7		4.42	%		1.19	%	$	73,251
	December 31, 2013
	Fair value hedges:
	Fixed rate long-term borrowings(a)		$	1,400,000			3.7		4.42	%		1.2	%	$	102,875
	(a)	Under the terms of these agreements, the Company receives settlement amounts at a fixed rate and pays at a variable rate.
	The notional amount of interest rate swap agreements entered into for risk management purposes that were outstanding at December 31, 2014 mature as follows:
			(In thousands)
	Year ending December 31:
	2016		$	500,000
	2017			400,000
	2018			500,000
			$	1,400,000
	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 $17.6 billion and $17.4 billion at December 31, 2014 and 2013, respectively. The notional amounts of foreign currency and other option and futures contracts entered into for trading account purposes aggregated $1.3 billion and $1.4 billion at December 31, 2014 and 2013, respectively.
	Information about the fair values of derivative instruments in the Company’s consolidated balance sheet and consolidated statement of income follows:
			Asset Derivatives					Liability Derivatives
			Fair Value					Fair Value
			December 31					December 31
			2014			2013		2014			2013
			(In thousands)
	Derivatives designated and qualifying as hedging instruments
	Fair value hedges:
	Interest rate swap agreements(a)		$	73,251		$	102,875	$	—		$	—
	Commitments to sell real estate loans(a)			728			6,957		4,217			487
				73,979			109,832		4,217			487
	Derivatives not designated and qualifying as hedging instruments
	Mortgage-related commitments to originate real estate loans for sale(a)			17,396			7,616		49			3,675
	Commitments to sell real estate loans(a)			754			6,120		4,330			230
	Trading:
	Interest rate contracts(b)			215,614			274,864		173,513			234,455
	Foreign exchange and other option and futures contracts(b)			31,112			15,831		29,950			15,342
				264,876			304,431		207,842			253,702
	Total derivatives		$	338,855		$	414,263	$	212,059		$	254,189
	(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.
			Amount of Unrealized Gain (Loss) Recognized
			Year Ended					Year Ended						Year Ended
			December 31, 2014					December 31, 2013						December 31, 2012
			Derivative			Hedged Item		Derivative			Hedged Item			Derivative			Hedged Item
			(In thousands)
	Derivatives in fair value hedging relationships
	Interest rate swap agreements:
	Fixed rate long-term borrowings(a)		$	(29,624	)	$	28,870	$	(40,304	)	$	38,986		$	(4,123	)	$	3,724
	Derivatives not designated as hedging instruments
	Trading:
	Interest rate contracts(b)		$	3,398				$	9,824					$	8,004
	Foreign exchange and other option and futures contracts(b)			(6,719	)				(3,369	)					(3,970	)
	Total		$	(3,321	)			$	6,455					$	4,034
	(a)	Reported as other revenues from operations.
	(b)	Reported as trading account and foreign exchange gains.
	In addition, 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 $28 million and $23 million at December 31, 2014 and 2013, 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 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, which are subject to enforceable master netting arrangements, was $161 million and $194 million at December 31, 2014 and 2013, respectively. After consideration of such netting arrangements, the net liability positions with counterparties aggregated $103 million and $107 million at December 31, 2014 and 2013, respectively. The Company was required to post collateral relating to those positions of $90 million and $95 million at December 31, 2014 and 2013, 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 to 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 December 31, 2014 was $22 million, for which the Company had posted collateral of $14 million in the normal course of business. If the credit risk-related contingent features had been triggered on December 31, 2014, the maximum amount of additional collateral the Company would have been required to post with counterparties was $8 million.
	The aggregate fair value of derivative financial instruments in an asset position, which are subject to enforceable master netting arrangements, was $104 million and $183 million at December 31, 2014 and 2013, respectively. After consideration of such netting arrangements, the net asset positions with counterparties aggregated $46 million and $95 million at December 31, 2014 and 2013, respectively. Counterparties posted collateral relating to those positions of $46 million and $93 million at December 31, 2014 and 2013, respectively. Trading account interest rate swap agreements entered into with customers are subject to the Company’s credit risk standards and often contain collateral provisions.
In addition to the derivative contracts noted above, the Company clears certain derivative transactions through a clearinghouse, rather than directly with counterparties. Those transactions cleared through a clearinghouse require initial margin collateral and additional collateral for contracts in a net liability position. The net fair values of derivative instruments cleared through clearinghouses at December 31, 2014 was a net liability position of $35 million and at December 31, 2013 was a net asset position of $5 million. Collateral posted with clearinghouses was $61 million and $14 million at December 31, 2014 and December 31, 2013, respectively.

Variable_interest_entities_and

Variable interest entities and asset securitizations	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
Variable interest entities and asset securitizations	19.    Variable interest entities and asset securitizations
	During 2013, the Company securitized approximately $3.0 billion of one-to-four family residential mortgage loans in guaranteed mortgage securitizations with Ginnie Mae. Approximately $1.3 billion of such loans were formerly held in the Company’s loan portfolio, whereas the remaining loans were newly originated. The Company recognized pre-tax gains of $42 million related to loans previously held for investment, which were recorded in “other revenues from operations,” and pre-tax gains of $28 million on newly originated loans, which were reflected in “mortgage banking revenues.” As a result of the securitization structure, the Company does not have effective control over the underlying loans and expects no material credit-related losses on the retained securities as a result of the guarantees by Ginnie Mae. In similar transactions during 2014, the Company securitized $133 million of one-to-four family residential real estate loans that had been originated for sale in guaranteed mortgage securitizations with Ginnie Mae and retained the resulting securities in its investment securities portfolio. Pre-tax gains on such transactions were not material. Additionally, in 2013 the Company securitized and sold approximately $1.4 billion of automobile loans that had been held in its loan portfolio. The Company recognized a gain of $21 million related to the sale, which was recorded in “other revenues from operations.” The Company continues to service the automobile loans, but has no other financial interest in the securitization trust that the loans were sold into. The Company has securitized loans to improve its regulatory capital ratios and strengthen its liquidity and risk profile as a result of changing regulatory liquidity and capital requirements.
	In accordance with GAAP, the Company determined that it was the primary beneficiary of a residential mortgage loan securitization trust considering its role as servicer and its retained subordinated interests in the trust. As a result, the Company has included the one-to-four family residential mortgage loans that were included in the trust in its consolidated financial statements. At December 31, 2014 and 2013, the carrying values of the loans in the securitization trust were $98 million and $121 million, respectively. The outstanding principal amount of mortgage-backed securities issued by the qualified special purpose trust that was held by parties unrelated to M&T at December 31, 2014 and 2013 was $15 million and $18 million, respectively. Because the transaction was non-recourse, the Company’s maximum exposure to loss as a result of its association with the trust at December 31, 2014 is limited to realizing the carrying value of the loans less the amount of the mortgage-backed securities held by third parties.
	As described in note 9, 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 December 31, 2014 and 2013, the Company included the junior subordinated debentures as “long-term borrowings” in its consolidated balance sheet. The Company has recognized $34 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 9.
	The Company has invested as a limited partner in various partnerships that collectively had total assets of approximately $1.2 billion at December 31, 2014 and $1.3 billion at December 31, 2013. 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 $243 million, including $56 million of unfunded commitments, at December 31, 2014 and $236 million, including $45 million of unfunded commitments, at December 31, 2013. 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.

Fair_value_measurements

Fair value measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair value measurements	20.    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 December 31, 2014.
	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 swap agreements and foreign exchange contracts with customers who require such services with offsetting positions with third parties to minimize the Company’s risk with respect to such transactions. The Company generally determines the fair value of its derivative trading account assets and liabilities using externally developed pricing models based on market observable inputs and, therefore, classifies such valuations as Level 2. Mutual funds held in connection with deferred compensation arrangements have been classified as Level 1 valuations. Valuations of investments in municipal and other bonds can generally be obtained through reference to quoted prices in less active markets for the same or similar securities or through model-based techniques in which all significant inputs are observable and, therefore, such valuations have been classified as Level 2.
	Investment securities available for sale
	The majority of the Company’s available-for-sale investment securities have been valued by reference to prices for similar securities or through model-based techniques in which all significant inputs are observable and, therefore, such valuations have been classified as Level 2. Certain investments in mutual funds and equity securities are actively traded and, therefore, have been classified as Level 1 valuations.
	As discussed in note 3, the Company sold substantially all of its privately issued mortgage-backed securities classified as available for sale during the second quarter of 2013. In prior periods, the Company generally used model-based techniques to value such securities because the Company was significantly restricted in the level of market observable assumptions that could be relied upon. Specifically, market assumptions regarding credit adjusted cash flows and liquidity influences on discount rates were difficult to observe at the individual bond level. Because of the inactivity in the markets and the lack of observable valuation inputs, the Company classified the valuation of privately issued mortgage-backed securities as Level 3.
	Included in collateralized debt obligations are securities backed by trust preferred securities issued by financial institutions and other entities. The Company could not obtain pricing indications for many of these securities from its two primary independent pricing sources. The Company, therefore, performed internal modeling to estimate the cash flows and fair value of its portfolio of securities backed by trust preferred securities at December 31, 2014 and 2013. The modeling techniques included estimating cash flows using bond-specific assumptions about future collateral defaults and related loss severities. The resulting cash flows were then discounted by reference to market yields observed in the single-name trust preferred securities market. In determining a market yield applicable to the estimated cash flows, a margin over LIBOR, ranging from 5% to 10% with a weighted-average of 8% was used. Significant unobservable inputs used in the determination of estimated fair value of collateralized debt obligations are included in the accompanying table of significant unobservable inputs to Level 3 measurements. At December 31, 2014, the total amortized cost and fair value of securities backed by trust preferred securities issued by financial institutions and other entities were $30 million and $50 million, respectively, and at December 31, 2013 were $42 million and $63 million, respectively. Privately issued mortgage-backed securities and securities backed by trust preferred securities issued by financial institutions and other entities constituted all of the available-for-sale investment securities classified as Level 3 valuations.
	The Company ensures an appropriate control framework is in place over the valuation processes and techniques used for significant Level 3 fair value measurements. Internal pricing models used for significant valuation measurements have generally been subjected to validation procedures including testing of mathematical constructs, review of valuation methodology and significant assumptions used.
	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.
	The following tables present assets and liabilities at December 31, 2014 and 2013 measured at estimated fair value on a recurring basis:
			Fair Value			Level 1(a)			Level 2(a)			Level 3
			Measurements at
			December 31,
			2014
			(In thousands)
	Trading account assets		$	308,175			51,416			256,759			—
	Investment securities available for sale:
	U.S. Treasury and federal agencies			161,947			—			161,947			—
	Obligations of states and political subdivisions			8,198			—			8,198			—
	Mortgage-backed securities:
	Government issued or guaranteed			8,731,123			—			8,731,123			—
	Privately issued			103			—			—			103
	Collateralized debt obligations			50,316			—			—			50,316
	Other debt securities			121,488			—			121,488			—
	Equity securities			83,757			64,841			18,916			—
				9,156,932			64,841			9,041,672			50,419
	Real estate loans held for sale			742,249			—			742,249			—
	Other assets(b)			92,129			—			74,733			17,396
	Total assets		$	10,299,485			116,257			10,115,413			67,815
	Trading account liabilities		$	203,464			—			203,464			—
	Other liabilities(b)			8,596			—			8,547			49
	Total liabilities		$	212,060			—			212,011			49
			Fair Value			Level 1(a)			Level 2(a)			Level 3
			Measurements  at
			December 31,
			2013
			(In thousands)
	Trading account assets		$	376,131			51,386			324,745			—
	Investment securities available for sale:
	U.S. Treasury and federal agencies			37,776			—			37,776			—
	Obligations of states and political subdivisions			10,811			—			10,811			—
	Mortgage-backed securities:
	Government issued or guaranteed			4,165,086			—			4,165,086			—
	Privately issued			1,850			—			—			1,850
	Collateralized debt obligations			63,083			—			—			63,083
	Other debt securities			120,085			—			120,085			—
	Equity securities			133,095			82,450			50,645			—
				4,531,786			82,450			4,384,403			64,933
	Real estate loans held for sale			468,650			—			468,650			—
	Other assets(b)			123,568			—			115,952			7,616
	Total assets		$	5,500,135			133,836			5,293,750			72,549
	Trading account liabilities		$	249,797			—			249,797			—
	Other liabilities(b)			4,392			—			717			3,675
Total liabilities		$	254,189			—			250,514			3,675
(a)	There were no significant transfers between Level 1 and Level 2 of the fair value hierarchy during the years ended December 31, 2014 and 2013.
(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).
The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the year ended December 31, 2014 were as follows:
		Investment Securities Available for Sale						Other
								Assets  and
								Other
		Privately Issued			Collateralized			Liabilities
		Mortgage-			Debt
		backed			Obligations
		Securities
		(In thousands)
Balance — January 1, 2014		$	1,850		$	63,083		$	3,941
Total gains realized/unrealized:
Included in earnings			—			—			83,417	(b)
Included in other comprehensive income			271	(e)		8,209	(e)		—
Settlements			(2,018	)		(20,976	)		—
Transfers in and/or out of Level 3(c)			—			—			(70,011	)(d)
Balance — December 31, 2014		$	103		$	50,316		$	17,347
Changes in unrealized gains included in earnings related to assets still held at December 31, 2014		$	—		$	—		$	18,196	(b)
The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the year ended December 31, 2013 were as follows:
		Investment Securities Available for Sale						Other
								Assets  and
								Other
		Privately			Collateralized			Liabilities
		Issued			Debt
		Mortgage-			Obligations
		backed
		Securities
		(In thousands)
Balance — January 1, 2013		$	1,023,886		$	61,869		$	47,859
Total gains (losses) realized/unrealized:
Included in earnings			(56,102	)(a)		—			97,845	(b)
Included in other comprehensive income			116,359	(e)		4,508	(e)		—
Sales			(978,608	)		—			—
Settlements			(103,685	)		(3,294	)		—
Transfers in and/or out of Level 3(c)			—			—			(141,763	)(d)
Balance — December 31, 2013		$	1,850		$	63,083		$	3,941
Changes in unrealized gains included in earnings related to assets still held at December 31, 2013		$	—		$	—		$	3,431	(b)
The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the year ended December 31, 2012 were as follows:
		Investment Securities Available for Sale						Other Assets
								and Other
		Privately			Collateralized			Liabilities
		Issued			Debt
		Mortgage-			Obligations
		backed
		Securities
		(In thousands)
Balance — January 1, 2012		$	1,151,285		$	52,500		$	6,923
Total gains (losses) realized/unrealized:
Included in earnings			(42,467	)(a)		—			212,281	(b)
Included in other comprehensive income			114,592	(e)		12,214	(e)		—
Settlements			(199,524	)		(2,845	)		—
Transfers in and/or out of Level 3(c)			—			—			(171,345	)(d)
Balance — December 31, 2012		$	1,023,886		$	61,869		$	47,859
Changes in unrealized gains (losses) included in earnings related to assets still held at December 31, 2012		$	(42,467	)(a)	$	—		$	47,859	(b)
(a)	Reported as an OTTI impairment loss or as gain (loss) on bank investment securities in the consolidated statement of income.
(b)	Reported as mortgage banking revenues in the consolidated statement of income and includes the fair value of commitment issuances and expirations.
(c)	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.
(d)	Transfers out of Level 3 consist of interest rate locks transferred to closed loans.
(e)	Reported as net unrealized gains on investment securities in the consolidated statement of comprehensive income.
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.
Investment securities held to maturity
During 2012, other-than-temporary losses of $5 million were recorded related to certain mortgage-backed securities. In accordance with GAAP, the carrying value of such securities was reduced to fair value, with estimated credit losses recognized in earnings and any remaining unrealized loss recognized in accumulated other comprehensive income. The determination of fair value included use of external and internal valuation sources that were weighted and averaged when estimating fair value. Due to the presence of significant unobservable inputs those valuations were classified as Level 3. The amortized cost, fair value and impact on the Company’s financial statements of the modeling described herein were not material. No such other-than-temporary losses were recorded in 2013 or 2014.
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 December 31, 2014. As these discounts are not readily observable and are considered significant, the valuations have been classified as Level 3. Loans subject to nonrecurring fair value measurement were $173 million at December 31, 2014, ($94 million and $79 million of which were classified as Level 2 and Level 3, respectively), $222 million at December 31, 2013 ($173 million and $49 million of which were classified as Level 2 and Level 3, respectively), and $335 million at December 31, 2012 ($207 million and $128 million of which were classified as Level 2 and Level 3, respectively). Changes in fair value recognized during the years ended December 31, 2014, 2013 and 2012 for partial charge-offs of loans and loan impairment reserves on loans held by the Company at the end of each of those years were decreases of $55 million, $58 million and $67 million, 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 $29 million at December 31, 2014 and December 31, 2013, respectively. Changes in fair value recognized for those foreclosed assets held by the Company were not material during each of 2014, 2013 and 2012.
Significant unobservable inputs to level 3 measurements
The following tables present quantitative information about significant unobservable inputs used in the fair value measurements for Level 3 assets and liabilities at December 31, 2014 and 2013:
		Fair Value at			Valuation		Unobservable	Range
		December  31,			Technique		Input/Assumptions	(Weighted-
		2014						Average)
		(In thousands)
Recurring fair value measurements:
Privately issued mortgage–backed securities		$	103		Two independent pricing quotes		—	—
Collateralized debt obligations			50,316		Discounted cash flow		Probability of default	12%-57% (36%)
							Loss severity	100%
Net other assets (liabilities)(a)			17,347		Discounted cash flow		Commitment expirations	0%-96% (17%)
(a)	Other Level 3 assets (liabilities) consist of commitments to originate real estate loans.
		Fair Value at			Valuation		Unobservable	Range
		December 31,			Technique		Input/Assumptions	(Weighted-
		2013						Average)
		(In thousands)
Recurring fair value measurements:
Privately issued mortgage–backed securities		$	1,850		Two independent pricing quotes		—	—
Collateralized debt obligations			63,083		Discounted cash flow		Probability of default	17%-55% (39%)
							Loss severity	100%
Net other assets (liabilities)(a)			3,941		Discounted cash flow		Commitment	0%-90% (20%)
							expirations
(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 probability of default and loss severity for collateralized debt securities would generally result in a lower (higher) fair value measurement.
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.
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:
		December 31, 2014
		Carrying			Estimated			Level 1			Level 2			Level 3
		Amount			Fair  Value
		(In thousands)
Financial assets:
Cash and cash equivalents		$	1,373,357		$	1,373,357		$	1,296,923		$	76,434		$	—
Interest-bearing deposits at banks			6,470,867			6,470,867			—			6,470,867			—
Trading account assets			308,175			308,175			51,416			256,759			—
Investment securities			12,993,542			13,023,956			64,841			12,750,396			208,719
Loans and leases:
Commercial loans and leases			19,461,292			19,188,574			—			—			19,188,574
Commercial real estate loans			27,567,569			27,487,818			—			307,667			27,180,151
Residential real estate loans			8,657,301			8,729,056			—			5,189,086			3,539,970
Consumer loans			10,982,794			10,909,623			—			—			10,909,623
Allowance for credit losses			(919,562	)		—			—			—			—
Loans and leases, net			65,749,394			66,315,071			—			5,496,753			60,818,318
Accrued interest receivable			227,348			227,348			—			227,348			—
Financial liabilities:
Noninterest-bearing deposits		$	(26,947,880	)	$	(26,947,880	)		—		$	(26,947,880	)		—
Savings deposits and NOW accounts			(43,393,618	)		(43,393,618	)		—			(43,393,618	)		—
Time deposits			(3,063,973	)		(3,086,126	)		—			(3,086,126	)		—
Deposits at Cayman Islands office			(176,582	)		(176,582	)		—			(176,582	)		—
Short-term borrowings			(192,676	)		(192,676	)		—			(192,676	)		—
Long-term borrowings			(9,006,959	)		(9,139,789	)		—			(9,139,789	)		—
Accrued interest payable			(63,372	)		(63,372	)		—			(63,372	)		—
Trading account liabilities			(203,464	)		(203,464	)		—			(203,464	)		—
Other financial instruments:
Commitments to originate real estate loans for sale		$	17,347		$	17,347			—		$	—		$	17,347
Commitments to sell real estate loans			(7,065	)		(7,065	)		—			(7,065	)		—
Other credit-related commitments			(119,079	)		(119,079	)		—			—			(119,079	)
Interest rate swap agreements used for interest rate risk management			73,251			73,251			—			73,251			—
		December 31, 2013
		Carrying			Estimated			Level 1			Level 2			Level 3
		Amount			Fair  Value
		(In thousands)
Financial assets:
Cash and cash equivalents		$	1,672,934		$	1,672,934		$	1,596,877		$	76,057		$	—
Interest-bearing deposits at banks			1,651,138			1,651,138			—			1,651,138			—
Trading account assets			376,131			376,131			51,386			324,745			—
Investment securities			8,796,497			8,690,494			82,450			8,384,106			223,938
Loans and leases:
Commercial loans and leases			18,705,216			18,457,288			—			—			18,457,288
Commercial real estate loans			26,148,208			26,018,195			—			67,505			25,950,690
Residential real estate loans			8,928,221			8,867,872			—			5,432,207			3,435,665
Consumer loans			10,291,514			10,201,087			—			—			10,201,087
Allowance for credit losses			(916,676	)		—			—			—			—
Loans and leases, net			63,156,483			63,544,442			—			5,499,712			58,044,730
Accrued interest receivable			222,558			222,558			—			222,558			—
Financial liabilities:
Noninterest-bearing deposits		$	(24,661,007	)	$	(24,661,007	)		—		$	(24,661,007	)		—
Savings deposits and NOW accounts			(38,611,021	)		(38,611,021	)		—			(38,611,021	)		—
Time deposits			(3,523,838	)		(3,542,789	)		—			(3,542,789	)		—
Deposits at Cayman Islands office			(322,746	)		(322,746	)		—			(322,746	)		—
Short-term borrowings			(260,455	)		(260,455	)		—			(260,455	)		—
Long-term borrowings			(5,108,870	)		(5,244,902	)		—			(5,244,902	)		—
Accrued interest payable			(43,419	)		(43,419	)		—			(43,419	)		—
Trading account liabilities			(249,797	)		(249,797	)		—			(249,797	)		—
Other financial instruments:
Commitments to originate real estate loans for sale		$	3,941		$	3,941			—		$	—		$	3,941
Commitments to sell real estate loans			12,360			12,360			—			12,360			—
Other credit-related commitments			(118,886	)		(118,886	)		—			—			(118,886	)
Interest rate swap agreements used for interest rate risk management			102,875			102,875			—			102,875			—
With the exception of marketable securities, certain off-balance sheet financial instruments and one-to-four family residential mortgage loans originated for sale, the Company’s financial instruments are not readily marketable and market prices do not exist. The Company, in attempting to comply with the provisions of GAAP that require disclosures of fair value of financial instruments, has not attempted to market its financial instruments to potential buyers, if any exist. Since negotiated prices in illiquid markets depend greatly upon the then present motivations of the buyer and seller, it is reasonable to assume that actual sales prices could vary widely from any estimate of fair value made without the benefit of negotiations. Additionally, changes in market interest rates can dramatically impact the value of financial instruments in a short period of time. The following assumptions, methods and calculations were used in determining the estimated fair value of financial instruments not measured at fair value in the consolidated balance sheet.
Cash and cash equivalents, interest-bearing deposits at banks, deposits at Cayman Islands office, short-term borrowings, accrued interest receivable and accrued interest payable
Due to the nature of cash and cash equivalents and the near maturity of interest-bearing deposits at banks, deposits at Cayman Islands office, short-term borrowings, accrued interest receivable and accrued interest payable, the Company estimated that the carrying amount of such instruments approximated estimated fair value.
Investment securities
Estimated fair values of investments in readily marketable securities were generally based on quoted market prices. Investment securities that were not readily marketable were assigned amounts based on estimates provided by outside parties or modeling techniques that relied upon discounted calculations of projected cash flows or, in the case of other investment securities, which include capital stock of the Federal Reserve Bank of New York and the Federal Home Loan Bank of New York, at an amount equal to the carrying amount.
Loans and leases
In general, discount rates used to calculate values for loan products were based on the Company’s pricing at the respective period end. A higher discount rate was assumed with respect to estimated cash flows associated with nonaccrual loans. Projected loan cash flows were adjusted for estimated credit losses. However, such estimates made by the Company may not be indicative of assumptions and adjustments that a purchaser of the Company’s loans and leases would seek.
Deposits
Pursuant to GAAP, the estimated fair value ascribed to noninterest-bearing deposits, savings deposits and NOW accounts must be established at carrying value because of the customers’ ability to withdraw funds immediately. Time deposit accounts are required to be revalued based upon prevailing market interest rates for similar maturity instruments. As a result, amounts assigned to time deposits were based on discounted cash flow calculations using prevailing market interest rates based on the Company’s pricing at the respective date for deposits with comparable remaining terms to maturity.
The Company believes that deposit accounts have a value greater than that prescribed by GAAP. The Company feels, however, that the value associated with these deposits is greatly influenced by characteristics of the buyer, such as the ability to reduce the costs of servicing the deposits and deposit attrition which often occurs following an acquisition.
Long-term borrowings
The amounts assigned to long-term borrowings were based on quoted market prices, when available, or were based on discounted cash flow calculations using prevailing market interest rates for borrowings of similar terms and credit risk.
Other commitments and contingencies
As described in note 21, in the normal course of business, various commitments and contingent liabilities are outstanding, such as loan commitments, credit guarantees and letters of credit. The Company’s pricing of such financial instruments is based largely on credit quality and relationship, probability of funding and other requirements. Loan commitments often have fixed expiration dates and contain termination and other clauses which provide for relief from funding in the event of significant deterioration in the credit quality of the customer. The rates and terms of the Company’s loan commitments, credit guarantees and letters of credit are competitive with other financial institutions operating in markets served by the Company. The Company believes that the carrying amounts, which are included in other liabilities, are reasonable estimates of the fair value of these financial instruments.
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	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	21.    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.
		December 31
		2014		2013
		(In thousands)
	Commitments to extend credit
	Home equity lines of credit	$	6,194,516	$	6,218,823
	Commercial real estate loans to be sold		212,257		62,386
	Other commercial real estate and construction		4,834,699		3,919,545
	Residential real estate loans to be sold		432,352		469,869
	Other residential real estate		524,399		384,617
	Commercial and other		11,080,856		10,419,545
	Standby letters of credit		3,706,888		3,600,528
	Commercial letters of credit		46,965		53,284
	Financial guarantees and indemnification contracts		2,490,050		2,457,633
	Commitments to sell real estate loans		1,237,294		854,656
	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 DUS program. The Company’s maximum credit risk for recourse associated with loans sold under this program totaled approximately $2.4 billion and $2.3 billion at December 31, 2014 and 2013, respectively.
	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 occupies certain banking offices and uses certain equipment under noncancelable operating lease agreements expiring at various dates over the next 24 years. Minimum lease payments under noncancelable operating leases are summarized in the following table:
		(In thousands)
	Year ending December 31:
	2015	$	87,063
	2016		83,315
	2017		70,108
	2018		56,024
	2019		45,079
	Later years		113,390
		$	454,979
	The Company is contractually obligated to repurchase previously sold residential real estate loans that do not ultimately meet investor sale criteria related to underwriting procedures or loan documentation. When required to do so, the Company may reimburse loan purchasers for losses incurred or may repurchase certain loans. The Company reduces residential mortgage banking revenues by an estimate for losses related to its obligations to loan purchasers. The amount of those charges is based on the volume of loans sold, the level of reimbursement requests received from loan purchasers and estimates of losses that may be associated with previously sold loans. At December 31, 2014, management believes that any further liability arising out of the Company’s obligation to loan purchasers is not material to the Company’s consolidated financial position.
	M&T and its subsidiaries are subject in the normal course of business to various pending and threatened legal proceedings 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 legal 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 $40 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	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segment information	22.    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 has been compiled utilizing the accounting policies described in note 1 with certain exceptions. The more significant of these exceptions are described herein. The Company allocates interest income or interest expense using a methodology that charges users of funds (assets) interest expense and credits providers of funds (liabilities) with income based on the maturity, prepayment and/or repricing characteristics of the assets and liabilities. The net effect of this allocation is recorded in the “All Other” category. A provision for credit losses is allocated to segments in an amount based largely on actual net charge-offs incurred by the segment during the period plus or minus an amount necessary to adjust the segment’s allowance for credit losses due to changes in loan balances. In contrast, the level of the consolidated provision for credit losses is determined using the methodologies described in notes 1 and 5. Indirect fixed and variable expenses incurred by certain centralized support areas are allocated to segments based on actual usage (for example, volume measurements) and other criteria. Certain types of administrative expenses and bankwide expense accruals (including amortization of core deposit and other intangible assets associated with acquisitions of financial institutions) are generally not allocated to segments. Income taxes are allocated to segments based on the Company’s marginal statutory tax rate adjusted for any tax-exempt income or non-deductible expenses. Equity is allocated to the segments based on regulatory capital requirements and in proportion to an assessment of the inherent risks associated with the business of the segment (including interest, credit and operating risk).
	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, reported segment results are 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. Information about the Company’s segments is presented in the accompanying table. Income statement amounts are in thousands of dollars. Balance sheet amounts are in millions of dollars.
												For the Years Ended December 31, 2014, 2013 and 2012
			Business Banking									Commercial Banking						Commercial Real Estate									Discretionary Portfolio
			2014			2013			2012			2014		2013		2012		2014			2013			2012			2014		2013			2012
	Net interest income(a)		$	317,356		$	325,521		$	347,067		$	745,218	$	758,231	$	753,678	$	539,600		$	570,786		$	531,398		$	74,204	$	66,157		$	66,303
	Noninterest income			105,370			102,945			103,283			259,832		263,766		253,808		127,445			130,895			133,120			27,464		(2,126	)		(76,113	)
				422,726			428,466			450,350			1,005,050		1,021,997		1,007,486		667,045			701,681			664,518			101,668		64,031			(9,810	)
	Provision for credit losses			18,885			26,450			22,245			33,197		76,818		15,781		(6,476	)		7,365			4,238			16,547		16,670			44,305
	Amortization of core deposit and other intangible assets			—			—			—			—		—		—		—			—			—			—		—			—
	Depreciation and other amortization			405			198			122			588		564		567		16,278			14,296			11,004			891		1,330			2,065
	Other noninterest expense			200,802			214,043			179,428			274,697		288,842		262,820		207,757			214,246			190,879			33,934		30,431			31,006
	Income (loss) before taxes			202,634			187,775			248,555			696,568		655,773		728,318		449,486			465,774			458,397			50,296		15,600			(87,186	)
	Income tax expense (benefit)			82,825			76,735			101,484			285,429		264,433		296,894		133,357			143,981			149,321			2,198		(14,368	)		(54,071	)
	Net income (loss)		$	119,809		$	111,040		$	147,071		$	411,139	$	391,340	$	431,424	$	316,129		$	321,793		$	309,076		$	48,098	$	29,968		$	(33,115	)
	Average total assets (in millions)		$	5,281		$	5,080		$	4,909		$	22,892	$	21,655	$	19,946	$	17,113		$	17,150		$	16,437		$	20,798	$	16,480		$	16,583
	Capital expenditures (in millions)		$	2		$	1		$	—		$	—	$	—	$	—	$	—		$	—		$	—		$	—	$	—		$	—
												For the Years Ended December 31, 2014, 2013 and 2012
			Residential Mortgage									Retail Banking						All Other									Total
			Banking
			2014			2013			2012			2014		2013		2012		2014			2013			2012			2014		2013			2012
	Net interest income(a)		$	90,123		$	98,496		$	78,058		$	741,109	$	810,134	$	902,906	$	168,836		$	43,904		$	(80,894	)	$	2,676,446	$	2,673,229		$	2,598,516
	Noninterest income			331,391			325,474			402,211			335,501		373,362		349,571		592,270			670,889			501,390			1,779,273		1,865,205			1,667,270
				421,514			423,970			480,269			1,076,610		1,183,496		1,252,477		761,106			714,793			420,496			4,455,719		4,538,434			4,265,786
	Provision for credit losses			(2,357	)		(11,711	)		17,169			77,158		72,502		95,345		(12,954	)		(3,094	)		4,917			124,000		185,000			204,000
	Amortization of core deposit and other intangible assets			—			—			—			—		—		—		33,824			46,912			60,631			33,824		46,912			60,631
	Depreciation and other amortization			47,108			48,716			46,902			37,788		34,599		32,734		61,848			57,120			50,536			164,906		156,823			143,930
	Other noninterest expense			222,396			225,794			195,604			759,569		768,644		751,916		844,972			690,150			693,046			2,544,127		2,432,150			2,304,699
	Income (loss) before taxes			154,367			161,171			220,594			202,095		307,751		372,482		(166,584	)		(76,295	)		(388,634	)		1,588,862		1,717,549			1,552,526
	Income tax expense (benefit)			59,361			61,779			85,671			82,179		125,350		151,616		(122,733	)		(78,841	)		(207,887	)		522,616		579,069			523,028
	Net income (loss)		$	95,006		$	99,392		$	134,923		$	119,916	$	182,401	$	220,866	$	(43,851	)	$	2,546		$	(180,747	)	$	1,066,246	$	1,138,480		$	1,029,498
	Average total assets (in millions)		$	3,333		$	2,858		$	2,451		$	10,449	$	10,997	$	11,705	$	12,277		$	9,442		$	7,952		$	92,143	$	83,662		$	79,983
	Capital expenditures (in millions)		$	—		$	—		$	1		$	14	$	40	$	15	$	57		$	89		$	76		$	73	$	130		$	92
	(a)	Net interest income is the difference between actual taxable-equivalent interest earned on assets and interest paid on liabilities by a segment and a funding charge (credit) based on the Company’s internal funds transfer pricing 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 $23,642,000 in 2014, $24,971,000 in 2013 and $26,391,000 in 2012 and is eliminated in “All Other” net interest income and income tax expense (benefit).
	The Business Banking segment provides deposit, lending, cash management and other financial services to small businesses and professionals through the Company’s banking office network and several other delivery channels, including business banking centers, telephone banking, Internet banking and automated teller machines. The Commercial Banking segment provides a wide range of credit products and banking services to middle-market and large commercial customers, mainly within the markets the Company serves. Among the services provided by this segment are commercial lending and leasing, letters of credit, deposit products and cash management services. The Commercial Real Estate segment provides credit services which are secured by various types of multifamily residential and commercial real estate and deposit services to its customers. Activities of this segment include the origination, sales and servicing of commercial real estate loans. The Discretionary Portfolio segment includes securities, residential mortgage loans and other assets; short-term and long-term borrowed funds; brokered deposits; and Cayman Islands branch deposits. This segment also provides foreign exchange services to customers. The Residential Mortgage Banking segment originates and services residential real estate loans for consumers and sells substantially all of those loans in the secondary market to investors or to the Discretionary Portfolio segment. The segment periodically purchases servicing rights to loans that have been originated by other entities. Residential real estate loans held for sale are included in the Residential Mortgage Banking segment. The Retail Banking segment offers a variety of services to consumers through several delivery channels that include banking offices, automated teller machines, telephone banking and Internet banking. The “All Other” category includes other operating activities of the Company that are not directly attributable to the reported segments; the difference between the provision for credit losses and the calculated provision allocated to the reportable segments; goodwill and core deposit and other intangible assets resulting from acquisitions of financial institutions; merger-related gains and expenses resulting from acquisitions; the net impact of the Company’s internal funds transfer pricing methodology; eliminations of transactions between reportable segments; certain nonrecurring transactions; the residual effects of unallocated support systems and general and administrative expenses; and the impact of interest rate risk management strategies. The amount of intersegment activity eliminated in arriving at consolidated totals was included in the “All Other” category as follows:
			Year Ended December 31
			2014			2013			2012
			(In thousands)
	Revenues		$	(49,800	)	$	(50,128	)	$	(71,452	)
	Expenses			(12,014	)		(16,235	)		(17,313	)
	Income taxes (benefit)			(15,375	)		(13,791	)		(22,029	)
	Net income (loss)			(22,411	)		(20,102	)		(32,110	)
	The Company conducts substantially all of its operations in the United States. There are no transactions with a single customer that in the aggregate result in revenues that exceed ten percent of consolidated total revenues.

Regulatory_matters

Regulatory matters	12 Months Ended
	Dec. 31, 2014
Banking and Thrift [Abstract]
Regulatory matters	23.    Regulatory matters
	Payment of dividends by M&T’s banking subsidiaries is restricted by various legal and regulatory limitations. Dividends from any banking subsidiary to M&T are limited by the amount of earnings of the banking subsidiary in the current year and the preceding two years. For purposes of this test, at December 31, 2014, approximately $1.5 billion was available for payment of dividends to M&T from banking subsidiaries. Additionally, the Federal Reserve Board requires bank holding companies with $50 billion or more of total consolidated assets to submit annual capital plans. Such bank holding companies may pay dividends and repurchase stock only in accordance with a capital plan which the Federal Reserve Board has not objected to.
	Banking regulations prohibit extensions of credit by the subsidiary banks to M&T unless appropriately secured by assets. Securities of affiliates are not eligible as collateral for this purpose.
	The bank subsidiaries are required to maintain reserves against certain deposit liabilities. During the maintenance periods that included December 31, 2014 and 2013, cash and due from banks and interest-earning deposits at banks included a daily average of $555,575,000 and $595,593,000, respectively, for such purpose.
	Federal regulators have adopted capital adequacy guidelines for bank holding companies and banks. Failure to meet minimum capital requirements can result in certain mandatory, and possibly additional discretionary, actions by regulators that, if undertaken, could have a material effect on the Company’s financial statements. Under the capital adequacy guidelines in effect through December 31, 2014, the so-called “Tier 1 capital” and “Total capital” as a percentage of risk-weighted assets and certain off-balance sheet financial instruments were required to be at least 4% and 8%, respectively. In addition to these risk-based measures, regulators also required banking institutions that met certain qualitative criteria to maintain a minimum “leverage” ratio of “Tier 1 capital” to average total assets, adjusted for goodwill and certain other items. As of December 31, 2014, M&T and each of its banking subsidiaries exceeded all applicable capital adequacy requirements. To be considered “well capitalized” under that regulatory framework, a banking institution had to maintain Tier 1 risk-based capital, total risk-based capital and leverage ratios of at least 6%, 10% and 5%, respectively.
	The capital ratios and amounts of the Company and its banking subsidiaries as of December 31, 2014 and 2013 are presented below:
			M&T			M&T Bank			Wilmington
			(Consolidated)						Trust,  N.A.
			(Dollars in thousands)
	December 31, 2014:
	Tier 1 capital
	Amount		$	9,644,765		$	8,043,185		$	435,558
	Ratio(a)			12.47	%		10.46	%		57.22	%
	Minimum required amount(b)			3,093,874			3,077,101			30,447
	Total capital
	Amount			11,767,308			10,048,277			439,867
	Ratio(a)			15.21	%		13.06	%		57.79	%
	Minimum required amount(b)			6,187,747			6,154,201			60,893
	Leverage
	Amount			9,644,765			8,043,185			435,558
	Ratio(c)			10.17	%		8.56	%		9.98	%
	Minimum required amount(b)			3,793,836			3,760,364			174,613
	December 31, 2013:
	Tier 1 capital
	Amount		$	8,792,035		$	7,341,506		$	420,330
	Ratio(a)			12	%		10.08	%		73.79	%
	Minimum required amount(b)			2,930,925			2,914,246			22,786
	Total capital
	Amount			11,045,589			9,445,770			424,975
	Ratio(a)			15.07	%		12.96	%		74.6	%
	Minimum required amount(b)			5,861,849			5,828,491			45,573
	Leverage
	Amount			8,792,035			7,341,506			420,330
	Ratio(c)			10.78	%		9.09	%		19.8	%
	Minimum required amount(b)			2,446,476			2,422,096			63,678
	(a)	The ratio of capital to risk-weighted assets, as defined by regulation.
	(b)	Minimum amount of capital to be considered adequately capitalized, as defined by regulation.
	(c)	The ratio of capital to average assets, as defined by regulation.
	Beginning in 2015, new regulatory capital rules became effective. The new rules substantially revise the risk-based capital requirements applicable to bank holding companies and banks. M&T and its subsidiary banks expect to be able to comply with the revised capital adequacy requirements.

Relationship_with_Bayview_Lend

Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P.	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P.	24.    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. The carrying value of that investment was $47 million at December 31, 2014.
	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 $4.8 billion and $5.5 billion at December 31, 2014 and 2013, respectively. Revenues from those servicing rights were $26 million, $31 million and $35 million during 2014, 2013 and 2012, respectively. The Company sub-services residential real estate loans for Bayview Financial having outstanding principal balances totaling $41.3 billion and $45.6 billion at December 31, 2014 and 2013, respectively. Revenues earned for sub-servicing loans for Bayview Financial were $115 million in 2014, $33 million in 2013 and $10 million in 2012. In addition, the Company held $202 million and $220 million of mortgage-backed securities in its held-to-maturity portfolio at December 31, 2014 and 2013, respectively, that were securitized by Bayview Financial.

Parent_company_financial_state

Parent company financial statements	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Parent company financial statements	25.    Parent company financial statements
	Condensed Balance Sheet
		December 31
		2014			2013
		(In thousands)
	Assets
	Cash in subsidiary bank	$	11,306		$	10,729
	Due from consolidated bank subsidiaries
	Money-market savings		1,096,533			968,274
	Current income tax receivable		—			1,914
	Other		12			1,894
	Total due from consolidated bank subsidiaries		1,096,545			972,082
	Investments in consolidated subsidiaries
	Banks and bank holding company		11,945,516			11,364,657
	Other		16,217			16,212
	Investments in unconsolidated subsidiaries (note 19)		33,578			33,751
	Investment in Bayview Lending Group LLC		46,716			73,883
	Other assets		81,034			80,098
	Total assets	$	13,230,912		$	12,551,412
	Liabilities
	Accrued expenses and other liabilities	$	59,950		$	62,817
	Long-term borrowings		835,066			1,183,063
	Total liabilities		895,016			1,245,880
	Shareholders’ equity		12,335,896			11,305,532
	Total liabilities and shareholders’ equity	$	13,230,912		$	12,551,412
	Condensed Statement of Income
		Year Ended December 31
		2014			2013			2012
		(In thousands, except per share)
	Income
	Dividends from consolidated bank subsidiaries	$	480,000		$	700,000		$	700,000
	Equity in earnings of Bayview Lending Group LLC		(16,672	)		(16,126	)		(21,511	)
	Other income		7,755			9,992			8,755
	Total income		471,083			693,866			687,244
	Expense
	Interest on long-term borrowings		47,700			73,115			82,286
	Other expense		15,107			15,994			19,226
	Total expense		62,807			89,109			101,512
	Income before income taxes and equity in undistributed income of subsidiaries		408,276			604,757			585,732
	Income tax credits		27,284			35,986			43,149
	Income before equity in undistributed income of subsidiaries		435,560			640,743			628,881
	Equity in undistributed income of subsidiaries
	Net income of subsidiaries		1,110,686			1,197,737			1,100,617
	Less: dividends received		(480,000	)		(700,000	)		(700,000	)
	Equity in undistributed income of subsidiaries		630,686			497,737			400,617
	Net income	$	1,066,246		$	1,138,480		$	1,029,498
	Net income per common share
	Basic	$	7.47		$	8.26		$	7.57
	Diluted		7.42			8.2			7.54
	Condensed Statement of Cash Flows
		Year Ended December 31
		2014			2013			2012
		(In thousands)
	Cash flows from operating activities
	Net income	$	1,066,246		$	1,138,480		$	1,029,498
	Adjustments to reconcile net income to net cash provided by operating activities
	Equity in undistributed income of subsidiaries		(630,686	)		(497,737	)		(400,617	)
	Provision for deferred income taxes		(6,522	)		1,535			1,724
	Net change in accrued income and expense		23,419			31,979			6,798
	Net cash provided by operating activities		452,457			674,257			637,403
	Cash flows from investing activities
	Proceeds from sales of investment securities		—			—			411
	Investment in subsidiary		—			(140,000	)		—
	Other, net		10,721			3,295			324
Net cash provided (used) by investing activities		10,721			(136,705	)		735
Cash flows from financing activities
Payments on long-term borrowings		(350,010	)		—			(300,000	)
Dividends paid — common		(371,199	)		(365,349	)		(357,717	)
Dividends paid — preferred		(70,234	)		(53,450	)		(53,450	)
Proceeds from issuance of preferred stock		346,500			—			—
Other, net		110,601			140,799			143,352
Net cash used by financing activities		(334,342	)		(278,000	)		(567,815	)
Net increase in cash and cash equivalents		128,836			259,552			70,323
Cash and cash equivalents at beginning of year		979,003			719,451			649,128
Cash and cash equivalents at end of year	$	1,107,839		$	979,003		$	719,451
Supplemental disclosure of cash flow information
Interest received during the year	$	2,094		$	2,224		$	1,970
Interest paid during the year		47,003			71,090			80,090
Income taxes received during the year		24,588			45,237			21,878

Significant_accounting_policie1

Significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Consolidation	Consolidation
	The consolidated financial statements include M&T and all of its subsidiaries. All significant intercompany accounts and transactions of consolidated subsidiaries have been eliminated in consolidation. The financial statements of M&T included in note 25 report investments in subsidiaries under the equity method. Information about some limited purpose entities that are affiliates of the Company but are not included in the consolidated financial statements appears in note 19.
Consolidated Statement of Cash Flows	Consolidated Statement of Cash Flows
	For purposes of this statement, cash and due from banks and federal funds sold are considered cash and cash equivalents.
Securities purchased under agreements to resell and securities sold under agreements to repurchase	Securities purchased under agreements to resell and securities sold under agreements to repurchase
	Securities purchased under agreements to resell and securities sold under agreements to repurchase are treated as collateralized financing transactions and are recorded at amounts equal to the cash or other consideration exchanged. It is generally the Company’s policy to take possession of collateral pledged to secure agreements to resell.
Trading account	Trading account
	Financial instruments used for trading purposes are stated at fair value. Realized gains and losses and unrealized changes in fair value of financial instruments utilized in trading activities are included in “trading account and foreign exchange gains” in the consolidated statement of income.
Investment securities	Investment securities
	Investments in debt securities are classified as held to maturity and stated at amortized cost when management has the positive intent and ability to hold such securities to maturity. Investments in other debt securities and equity securities having readily determinable fair values are classified as available for sale and stated at estimated fair value. Amortization of premiums and accretion of discounts for investment securities available for sale and held to maturity are included in interest income.
	Other securities are stated at cost and include stock of the Federal Reserve Bank of New York and the Federal Home Loan Bank (“FHLB”) of New York.
	The cost basis of individual securities is written down through a charge to earnings when declines in value below amortized cost are considered to be other than temporary. In cases where fair value is less than amortized cost and the Company intends to sell a debt security, it is more likely than not to be required to sell a debt security before recovery of its amortized cost basis, or the Company does not expect to recover the entire amortized cost basis of a debt security, an other-than-temporary impairment is considered to have occurred. If the Company intends to sell the debt security or more likely than not will be required to sell the security before recovery of its amortized cost basis, the other-than-temporary impairment is recognized in earnings equal to the entire difference between the debt security’s amortized cost basis and its fair value. If the Company does not expect to recover the entire amortized cost basis of the security, the Company does not intend to sell the security and it is not more likely than not that the Company will be required to sell the security before recovery of its amortized cost basis, the other-than-temporary impairment is separated into (a) the amount representing the credit loss and (b) the amount related to all other factors. The amount of the other-than-temporary impairment related to the credit loss is recognized in earnings while the amount related to other factors is recognized in other comprehensive income, net of applicable taxes. Subsequently, the Company accounts for the other-than-temporarily impaired debt security as if the security had been purchased on the measurement date of the other-than-temporary impairment at an amortized cost basis equal to the previous amortized cost basis less the other-than-temporary impairment recognized in earnings. The cost basis of individual equity securities is written down to estimated fair value through a charge to earnings when declines in value below cost are considered to be other than temporary. Realized gains and losses on the sales of investment securities are determined using the specific identification method.
Loans and leases	Loans and leases
	The Company’s accounting methods for loans depends on whether the loans were originated by the Company or were acquired in a business combination.
	Originated loans and leases
	Interest income on loans is accrued on a level yield method. Loans are placed on nonaccrual status and previously accrued interest thereon is charged against income when principal or interest is delinquent 90 days, unless management determines that the loan status clearly warrants other treatment. Nonaccrual commercial loans and commercial real estate loans are returned to accrual status when borrowers have demonstrated an ability to repay their loans and there are no delinquent principal and interest payments. Consumer loans not secured by residential real estate are returned to accrual status when all past due principal and interest payments have been paid by the borrower. Loans secured by residential real estate are returned to accrual status when they are deemed to have an insignificant delay in payments of 90 days or less. Loan balances are charged off when it becomes evident that such balances are not fully collectible. For commercial loans and commercial real estate loans, charge-offs are recognized after an assessment by credit personnel of the capacity and willingness of the borrower to repay, the estimated value of any collateral, and any other potential sources of repayment. A charge-off is recognized when, after such assessment, it becomes evident that the loan balance is not fully collectible. For loans secured by residential real estate, the excess of the loan balances over the net realizable value of the property collateralizing the loan is charged-off when the loan becomes 150 days delinquent. Consumer loans are generally charged-off when the loans are 91 to 180 days past due, depending on whether the loan is collateralized and the status of repossession activities with respect to such collateral. Loan fees and certain direct loan origination costs are deferred and recognized as an interest yield adjustment over the life of the loan. Net deferred fees have been included in unearned discount as a reduction of loans outstanding. Commitments to sell real estate loans are utilized by the Company 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 recorded in the consolidated balance sheet includes changes in estimated fair market value during the hedge period, typically from the date of close through the sale date. Valuation adjustments made on these loans and commitments are included in “mortgage banking revenues.”
	Except for consumer and residential mortgage loans that are considered smaller balance homogenous loans and are evaluated collectively, the Company considers a loan to be impaired for purposes of applying GAAP when, based on current information and events, it is probable that the Company will be unable to collect all amounts according to the contractual terms of the loan agreement or the loan is delinquent 90 days. Regardless of loan type, the Company considers a loan to be impaired if it qualifies as a troubled debt restructuring. Impaired loans are classified as either nonaccrual or as loans renegotiated at below market rates which continue to accrue interest, provided that a credit assessment of the borrower’s financial condition results in an expectation of full repayment under the modified contractual terms. Certain loans greater than 90 days delinquent are not considered impaired if they are well-secured and in the process of collection. Loans less than 90 days delinquent are deemed to have an insignificant delay in payment and are generally not considered impaired. Impairment of a loan is measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate, the loan’s observable market price, or the fair value of collateral if the loan is collateral-dependent. Interest received on impaired loans placed on nonaccrual status is generally applied to reduce the carrying value of the loan or, if principal is considered fully collectible, recognized as interest income.
	Residual value estimates for commercial leases are generally determined through internal or external reviews of the leased property. The Company reviews commercial lease residual values at least annually and recognizes residual value impairments deemed to be other than temporary.
	Loans and leases acquired in a business combination
	Loans acquired in a business combination subsequent to December 31, 2008 are recorded at fair value with no carry-over of an acquired entity’s previously established allowance for credit losses. The excess of cash flows expected at acquisition over the estimated fair value of acquired loans is recognized as interest income over the remaining lives of the loans. Subsequent decreases in the expected principal cash flows require the Company to evaluate the need for additions to the Company’s allowance for credit losses. Subsequent improvements in expected cash flows result first in the recovery of any related allowance for credit losses and then in recognition of additional interest income over the then-remaining lives of the loans.
	Purchased impaired loans represent specifically identified loans with evidence of credit deterioration for which it was probable at acquisition that the Company would be unable to collect all contractual principal and interest payments.
Allowance for credit losses	Allowance for credit losses
	The allowance for credit losses represents, in management’s judgment, the amount of losses inherent in the loan and lease portfolio as of the balance sheet date. The allowance is determined by management’s evaluation of the loan and lease portfolio based on such factors as the differing economic risks associated with each loan category, the current financial condition of specific borrowers, the economic environment in which borrowers operate, the level of delinquent loans, the value of any collateral and, where applicable, the existence of any guarantees or indemnifications. The effects of probable decreases in expected principal cash flows on acquired loans are also considered in the establishment of the allowance for credit losses.
Assets taken in foreclosure of defaulted loans	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 included in “other assets” in the consolidated balance sheet. Upon acquisition of assets taken in satisfaction of a defaulted loan, the excess of the remaining loan balance over the asset’s estimated fair value less costs to sell is charged off against the allowance for credit losses. Subsequent declines in value of the assets are recognized as “other costs of operations” in the consolidated statement of income.
Premises and equipment	Premises and equipment
	Premises and equipment are stated at cost less accumulated depreciation. Depreciation expense is computed principally using the straight-line method over the estimated useful lives of the assets.
Capitalized servicing rights	Capitalized servicing rights
	Capitalized servicing assets are included in “other assets” in the consolidated balance sheet. Separately recognized servicing assets are initially measured at fair value. The Company uses the amortization method to subsequently measure servicing assets. Under that method, capitalized servicing assets are charged to expense in proportion to and over the period of estimated net servicing income.
	To estimate the fair value of servicing rights, the Company considers market prices for similar assets and the present value of expected future cash flows associated with the servicing rights calculated using assumptions that market participants would use in estimating future servicing income and expense. Such assumptions include estimates of the cost of servicing loans, loan default rates, an appropriate discount rate, and prepayment speeds. For purposes of evaluating and measuring impairment of capitalized servicing rights, the Company stratifies such assets based on the predominant risk characteristics of the underlying financial instruments that are expected to have the most impact on projected prepayments, cost of servicing and other factors affecting future cash flows associated with the servicing rights. Such factors may include financial asset or loan type, note rate and term. The amount of impairment recognized is the amount by which the carrying value of the capitalized servicing rights for a stratum exceeds estimated fair value. Impairment is recognized through a valuation allowance.
Sales and securitizations of financial assets	Sales and securitizations of financial assets
	Transfers of financial assets for which the Company has surrendered control of the financial assets are accounted for as sales. Interests in a sale of financial assets that continue to be held by the Company, including servicing rights, are measured at fair value. The fair values of retained debt securities are generally determined through reference to independent pricing information. The fair values of retained servicing rights and any other retained interests are determined based on the present value of expected future cash flows associated with those interests and by reference to market prices for similar assets.
	Securitization structures typically require the use of special-purpose trusts that are considered variable interest entities. A variable interest entity is included in the consolidated financial statements if the Company has the power to direct the activities that most significantly impact the variable interest entity’s economic performance and has the obligation to absorb losses or the right to receive benefits of the variable interest entity that could potentially be significant to that entity.
Goodwill and core deposit and other intangible assets	Goodwill and core deposit and other intangible assets
	Goodwill represents the excess of the cost of an acquired entity over the fair value of the identifiable net assets acquired. Goodwill is not amortized, but rather is tested for impairment at least annually at the reporting unit level, which is either at the same level or one level below an operating segment. Other acquired intangible assets with finite lives, such as core deposit intangibles, are initially recorded at estimated fair value and are amortized over their estimated lives. Core deposit and other intangible assets are generally amortized using accelerated methods over estimated useful lives of five to ten years. The Company periodically assesses whether events or changes in circumstances indicate that the carrying amounts of core deposit and other intangible assets may be impaired.
Derivative financial instruments	Derivative financial instruments
	The Company accounts for derivative financial instruments at fair value. If certain conditions are met, a derivative may be specifically designated as (a) a hedge of the exposure to changes in the fair value of a recognized asset or liability or an unrecognized firm commitment, (b) a hedge of the exposure to variable cash flows of a forecasted transaction or (c) a hedge of the foreign currency exposure of a net investment in a foreign operation, an unrecognized firm commitment, an available-for-sale security, or a foreign currency denominated forecasted transaction.
	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. For such agreements, amounts receivable or payable are recognized as accrued under the terms of the agreement and the net differential is recorded as an adjustment to interest income or expense of the related asset or liability. Interest rate swap agreements may be designated as either fair value hedges or cash flow hedges. In a fair value hedge, the fair values of the interest rate swap agreements and changes in the fair values of the hedged items are recorded in the Company’s consolidated balance sheet with the corresponding gain or loss recognized in current earnings. The difference between changes in the fair values of interest rate swap agreements and the hedged items represents hedge ineffectiveness and is recorded in “other revenues from operations” in the consolidated statement of income. In a cash flow hedge, the effective portion of the derivative’s unrealized gain or loss is initially recorded as a component of other comprehensive income and subsequently reclassified into earnings when the forecasted transaction affects earnings. The ineffective portion of the unrealized gain or loss is reported in “other revenues from operations” immediately.
	The Company utilizes commitments to sell real estate loans to hedge the exposure to changes in the fair value of real estate loans held for sale. Commitments to originate real estate loans to be held for sale and commitments to sell real estate loans are generally recorded in the consolidated balance sheet at estimated fair market value.
	Derivative instruments not related to mortgage banking activities, including financial futures commitments and interest rate swap agreements, that do not satisfy the hedge accounting requirements are recorded at fair value and are generally classified as trading account assets or liabilities with resultant changes in fair value being recognized in “trading account and foreign exchange gains” in the consolidated statement of income.
Stock-based compensation	Stock-based compensation
	Stock-based compensation expense is recognized over the vesting period of the stock-based grant based on the estimated grant date value of the stock-based compensation that is expected to vest, except that the recognition of compensation costs is accelerated for stock-based awards granted to retirement-eligible employees and employees who will become retirement-eligible prior to full vesting of the award because the Company’s incentive compensation plan allows for vesting at the time an employee retires.
Income taxes	Income taxes
	Deferred tax assets and liabilities are recognized for the future tax effects attributable to differences between the financial statement value of existing assets and liabilities and their respective tax bases and carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates and laws.
	The Company evaluates uncertain tax positions using the two-step process required by GAAP. The first step requires a determination of whether it is more likely than not that a tax position will be sustained upon examination, including resolution of any related appeals or litigation processes, based on the technical merits of the position. Under the second step, a tax position that meets the more-likely-than-not recognition threshold is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement.
Earnings per common share	Earnings per common share
	Basic earnings per common share exclude dilution and are computed by dividing income available to common shareholders by the weighted-average number of common shares outstanding (exclusive of shares represented by the unvested portion of restricted stock and restricted stock unit grants) and common shares issuable under deferred compensation arrangements during the period. Diluted earnings per common share reflect shares represented by the unvested portion of restricted stock and restricted stock unit grants and the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in earnings. Proceeds assumed to have been received on such exercise or conversion are assumed to be used to purchase shares of M&T common stock at the average market price during the period, as required by the “treasury stock method” of accounting.
	GAAP requires that unvested share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents (whether paid or unpaid) shall be considered participating securities and 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 that contain such rights and, accordingly, the Company’s earnings per common share are calculated using the two-class method.
Treasury stock	Treasury stock
	Repurchases of shares of M&T common stock are recorded at cost as a reduction of shareholders’ equity. Reissuances of shares of treasury stock are recorded at average cost.

Acquisitions_Tables

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Summary of Merger-Related Expenses	A summary of merger-related expenses included in the consolidated statement of income for the years ended December 31, 2013 and 2012 follows:
		2013		2012
		(In thousands)
	Salaries and employee benefits	$	836	$	4,997
	Equipment and net occupancy		690		15
	Printing, postage and supplies		1,825		—
	Other costs of operations		9,013		4,867
		$	12,364	$	9,879

Investment_securities_Tables

Investment securities (Tables)	12 Months Ended
	Dec. 31, 2014
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		Gross			Gross		Estimated
		Cost		Unrealized			Unrealized		Fair  Value
				Gains			Losses
		(In thousands)
	December 31, 2014
	Investment securities available for sale:
	U.S. Treasury and federal agencies	$	161,408	$	544		$	5	$	161,947
	Obligations of states and political subdivisions		8,027		224			53		8,198
	Mortgage-backed securities:
	Government issued or guaranteed		8,507,571		223,889			337		8,731,123
	Privately issued		104		2			3		103
	Collateralized debt obligations		30,073		21,276			1,033		50,316
	Other debt securities		138,240		1,896			18,648		121,488
	Equity securities		73,901		11,020			1,164		83,757
			8,919,324		258,851			21,243		9,156,932
	Investment securities held to maturity:
	Obligations of states and political subdivisions		148,961		2,551			189		151,323
	Mortgage-backed securities:
	Government issued or guaranteed		3,149,320		78,485			7,000		3,220,805
	Privately issued		201,733		1,143			44,576		158,300
	Other debt securities		7,854		—			—		7,854
			3,507,868		82,179			51,765		3,538,282
	Other securities		328,742		—			—		328,742
	Total	$	12,755,934	$	341,030		$	73,008	$	13,023,956
	December 31, 2013
	Investment securities available for sale:
	U.S. Treasury and federal agencies	$	37,396	$	382		$	2	$	37,776
	Obligations of states and political subdivisions		10,484		333			6		10,811
	Mortgage-backed securities:
	Government issued or guaranteed		4,123,435		61,001			19,350		4,165,086
	Privately issued		1,468		387			5		1,850
	Collateralized debt obligations		42,274		21,666			857		63,083
	Other debt securities		137,828		1,722			19,465		120,085
	Equity securities		91,480		41,842			227		133,095
			4,444,365		127,333			39,912		4,531,786
	Investment securities held to maturity:
	Obligations of states and political subdivisions		169,684		3,744			135		173,293
	Mortgage-backed securities:
	Government issued or guaranteed		3,567,905		16,160			65,149		3,518,916
	Privately issued		219,628		—			60,623		159,005
	Other debt securities		8,913		—			—		8,913
			3,966,130		19,904			125,907		3,860,127
	Other securities		298,581		—			—		298,581
	Total	$	8,709,076	$	147,237		$	165,819	$	8,690,494
Investment Ratings of All Privately Issued Mortgage-Backed Securities, Collateralized Debt Obligations and Other Debt Securities	As of December 31, 2014, the latest available investment ratings of all obligations of states and political subdivisions, privately issued mortgage-backed securities, collateralized debt obligations and other debt securities were:
		Amortized		Estimated			Average Credit Rating of Fair Value Amount
		Cost		Fair Value			A or Better		BBB			BB		B or Less		Not Rated
		(In thousands)
	Obligations of states and political subdivisions	$	156,988	$	159,521		$	137,606	$	—		$	—	$	—	$	21,915
	Privately issued mortgage-backed securities		201,837		158,403			48,368		19			—		109,949		67
	Collateralized debt obligations		30,073		50,316			6,629		5,488			1,273		36,926		—
	Other debt securities		146,094		129,342			12,352		58,481			29,028		20,400		9,081
	Total	$	534,992	$	497,582		$	204,955	$	63,988		$	30,301	$	167,275	$	31,063
Amortized Cost and Estimated Fair Value of Collateralized Mortgage Obligations	The amortized cost and estimated fair value of collateralized mortgage obligations included in mortgage-backed securities were as follows:
		December 31
		2014		2013
		(In thousands)
	Collateralized mortgage obligations:
	Amortized cost	$	209,107	$	231,040
	Estimated fair value		165,860		171,100
Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity	At December 31, 2014, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:
		Amortized		Estimated
		Cost		Fair Value
		(In thousands)
	Debt securities available for sale:
	Due in one year or less	$	7,412	$	7,468
	Due after one year through five years		164,412		165,340
	Due after five years through ten years		3,524		3,577
	Due after ten years		162,400		165,564
			337,748		341,949
	Mortgage-backed securities available for sale		8,507,675		8,731,226
		$	8,845,423	$	9,073,175
	Debt securities held to maturity:
	Due in one year or less	$	23,107	$	23,254
	Due after one year through five years		84,112		85,457
	Due after five years through ten years		41,742		42,612
	Due after ten years		7,854		7,854
			156,815		159,177
	Mortgage-backed securities held to maturity		3,351,053		3,379,105
		$	3,507,868	$	3,538,282
Investment Securities in Continuous Unrealized Loss Position	A summary of investment securities that as of December 31, 2014 and 2013 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			Fair Value		Unrealized
				Losses					Losses
		(In thousands)
	December 31, 2014
	Investment securities available for sale:
	U.S. Treasury and federal agencies	$	6,505	$	(5	)	$	—	$	—
	Obligations of states and political subdivisions		1,785		(52	)		121		(1	)
	Mortgage-backed securities:
	Government issued or guaranteed		39,001		(186	)		5,555		(151	)
	Privately issued		—		—			65		(3	)
	Collateralized debt obligations		2,108		(696	)		5,512		(337	)
	Other debt securities		14,017		(556	)		92,661		(18,092	)
	Equity securities		2,138		(1,164	)		—		—
			65,554		(2,659	)		103,914		(18,584	)
	Investment securities held to maturity:
	Obligations of states and political subdivisions		29,886		(184	)		268		(5	)
	Mortgage-backed securities:
	Government issued or guaranteed		137,413		(361	)		446,780		(6,639	)
	Privately issued		—		—			127,512		(44,576	)
			167,299		(545	)		574,560		(51,220	)
	Total	$	232,853	$	(3,204	)	$	678,474	$	(69,804	)
	December 31, 2013
	Investment securities available for sale:
	U.S. Treasury and federal agencies	$	745	$	(2	)	$	—	$	—
	Obligations of states and political subdivisions		—		—			558		(6	)
	Mortgage-backed securities:
	Government issued or guaranteed		1,697,094		(19,225	)		5,815		(125	)
	Privately issued		—		—			98		(5	)
	Collateralized debt obligations		—		—			6,257		(857	)
	Other debt securities		1,428		(4	)		103,602		(19,461	)
	Equity securities		159		(227	)		—		—
			1,699,426		(19,458	)		116,330		(20,454	)
	Investment securities held to maturity:
	Obligations of states and political subdivisions		13,517		(120	)		1,558		(15	)
	Mortgage-backed securities:
	Government issued or guaranteed		2,629,950		(65,149	)		—		—
	Privately issued		—		—			159,005		(60,623	)
			2,643,467		(65,269	)		160,563		(60,638	)
	Total	$	4,342,893	$	(84,727	)	$	276,893	$	(81,092	)

Loans_and_leases_Tables

Loans and leases (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Total Loans and Leases Outstanding	Total loans and leases outstanding were comprised of the following:
			December 31
			2014			2013
			(In thousands)
	Loans
	Commercial, financial, etc.		$	18,280,049		$	17,477,238
	Real estate:
	Residential			8,636,794			8,911,554
	Commercial			22,614,174			21,799,886
	Construction			5,061,269			4,457,650
	Consumer			10,969,879			10,280,527
	Total loans			65,562,165			62,926,855
	Leases
	Commercial			1,337,204			1,398,928
	Total loans and leases			66,899,369			64,325,783
	Less: unearned discount			(230,413	)		(252,624	)
	Total loans and leases, net of unearned discount		$	66,668,956		$	64,073,159
Outstanding Principal Balance and Carrying Amount of Loans that is Included in Consolidated Balance Sheet	The outstanding principal balance and the carrying amount of acquired loans that were recorded at fair value at the acquisition date that is included in the consolidated balance sheet were as follows:
			December 31
			2014			2013
			(In thousands)
	Outstanding principal balance		$	3,070,268		$	4,656,811
	Carrying amount:
	Commercial, financial, leasing, etc.			247,820			580,685
	Commercial real estate			961,828			1,541,368
	Residential real estate			453,360			576,473
	Consumer			933,537			1,308,926
			$	2,596,545		$	4,007,452
Summary of Changes in Accretable Yield for Acquired Loans	A summary of changes in the accretable yield for acquired loans for the years ended December 31, 2014, 2013 and 2012 follows:
	For Year Ended December 31,		2014						2013						2012
			Purchased			Other			Purchased			Other			Purchased			Other
			Impaired			Acquired			Impaired			Acquired			Impaired			Acquired
			(In thousands)
	Balance at beginning of period		$	37,230		$	538,633		$	42,252		$	638,272		$	30,805		$	807,960
	Interest income			(21,263	)		(178,670	)		(36,727	)		(247,295	)		(40,551	)		(295,654	)
	Reclassifications from nonaccretable balance, net			60,551			24,907			31,705			149,595			51,998			148,490
	Other(a)			—			12,509			—			(1,939	)		—			(22,524	)
	Balance at end of period		$	76,518		$	397,379		$	37,230		$	538,633		$	42,252		$	638,272
	(a)	Other changes in expected cash flows including changes in interest rates and prepayment assumptions.
Summary of Current, Past Due and Nonaccrual Loans	A summary of current, past due and nonaccrual loans as of December 31, 2014 and 2013 follows:
									90 Days or More Past
									Due and Accruing
			Current			30-89 Days			Non-			Acquired(a)			Purchased			Nonaccrual			Total
						Past Due			acquired						Impaired(b)
			(In thousands)
	December 31, 2014
	Commercial, financial, leasing, etc.		$	19,228,265		$	37,246		$	1,805		$	6,231		$	10,300		$	177,445		$	19,461,292
	Real estate:
	Commercial			22,208,491			118,704			22,170			14,662			51,312			141,600			22,556,939
	Residential builder and developer			1,273,607			11,827			492			9,350			98,347			71,517			1,465,140
	Other commercial construction			3,484,932			17,678			—			—			17,181			25,699			3,545,490
	Residential			7,640,368			226,932			216,489			35,726			18,223			180,275			8,318,013
	Residential Alt-A			249,810			11,774			—			—			—			77,704			339,288
	Consumer:
	Home equity lines and loans			5,859,378			42,945			—			27,896			2,374			89,291			6,021,884
	Automobile			1,931,138			30,500			—			133			—			17,578			1,979,349
	Other			2,909,791			33,295			4,064			16,369			—			18,042			2,981,561
	Total		$	64,785,780		$	530,901		$	245,020		$	110,367		$	197,737		$	799,151		$	66,668,956
	December 31, 2013
	Commercial, financial, leasing, etc.		$	18,489,474		$	77,538		$	4,981		$	6,778		$	15,706		$	110,739		$	18,705,216
	Real estate:
	Commercial			21,236,071			145,749			63,353			35,603			88,034			173,048			21,741,858
	Residential builder and developer			1,025,984			8,486			141			7,930			137,544			96,427			1,276,512
	Other commercial construction			2,986,598			42,234			—			8,031			57,707			35,268			3,129,838
	Residential			7,630,368			295,131			294,649			43,700			29,184			252,805			8,545,837
	Residential Alt-A			283,253			18,009			—			—			—			81,122			382,384
	Consumer:
	Home equity lines and loans			5,972,365			40,537			—			27,754			2,617			78,516			6,121,789
	Automobile			1,314,246			29,144			—			366			—			21,144			1,364,900
	Other			2,726,522			47,830			5,386			—			—			25,087			2,804,825
	Total		$	61,664,881		$	704,658		$	368,510		$	130,162		$	330,792		$	874,156		$	64,073,159
	(a)	Acquired loans that were recorded at fair value at acquisition date. This category does not include purchased impaired loans that are presented separately.
	(b)	Accruing loans that were impaired at acquisition date and were recorded at fair value.
Loan Modification Activities that were Considered Troubled Debt Restructurings	The table below summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the year ended December 31, 2014:
						Recorded Investment						Financial Effects of
												Modification
			Number			Pre-			Post-			Recorded			Interest
						modifica-			modifica-			Investment			(b)
						tion			tion			(a)
			(Dollars in thousands)
	Commercial, financial, leasing, etc.
	Principal deferral			95		$	29,035		$	23,628		$	(5,407	)	$	—
	Other			3			29,912			31,604			1,692			—
	Combination of concession types			7			19,167			19,030			(137	)		(20	)
	Real estate:
	Commercial
	Principal deferral			39			19,077			18,997			(80	)		—
	Interest rate reduction			1			255			252			(3	)		(48	)
	Other			1			650			—			(650	)		—
	Combination of concession types			7			1,152			1,198			46			(264	)
	Residential builder and developer
	Principal deferral			2			1,639			1,639			—			—
	Other commercial construction
	Principal deferral			4			6,703			6,611			(92	)		—
	Residential
	Principal deferral			28			2,710			2,905			195			—
	Interest rate reduction			11			1,146			1,222			76			(152	)
	Other			1			188			188			—			—
	Combination of concession types			30			4,211			4,287			76			(483	)
	Residential Alt-A
	Principal deferral			6			880			963			83			—
	Combination of concession types			21			3,806			3,846			40			(386	)
	Consumer:
	Home equity lines and loans
	Principal deferral			3			280			280			—			—
	Interest rate reduction			6			535			535			—			(120	)
	Combination of concession types			47			5,031			5,031			—			(560	)
	Automobile
	Principal deferral			208			3,293			3,293			—			—
	Interest rate reduction			9			152			152			—			(12	)
	Other			42			255			255			—			—
	Combination of concession types			81			1,189			1,189			—			(100	)
	Other
	Principal deferral			33			245			245			—			—
	Interest rate reduction			4			293			293			—			(63	)
	Other			1			45			45			—			—
	Combination of concession types			70			2,502			2,502			—			(761	)
	Total			760		$	134,351		$	130,190		$	(4,161	)	$	(2,969	)
	(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages.
	(b)	Represents the present value of interest rate concessions discounted at the effective rate of the original loan.
	The table below summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the year ended December 31, 2013:
						Recorded Investment						Financial Effects of
												Modification
			Number			Pre-			Post-			Recorded			Interest
						modifica-			modifica-			Investment			(b)
						tion			tion			(a)
			(Dollars in thousands)
	Commercial, financial, leasing, etc.
	Principal deferral			79		$	16,389		$	16,002		$	(387	)	$	—
	Interest rate reduction			1			104			335			231			(54	)
	Other			4			50,433			50,924			491			—
	Combination of concession types			11			6,229			5,578			(651	)		(458	)
	Real estate:
	Commercial
	Principal deferral			27			40,639			40,464			(175	)		—
	Other			2			449			475			26			—
	Combination of concession types			9			2,649			3,040			391			(250	)
Residential builder and developer
Principal deferral			18			21,423			20,577			(846	)		—
Other			1			4,039			3,888			(151	)		—
Combination of concession types			3			15,580			15,514			(66	)		(535	)
Other commercial construction
Principal deferral			3			590			521			(69	)		—
Residential
Principal deferral			32			3,556			3,821			265			—
Other			1			195			195			—			—
Combination of concession types			61			73,940			70,854			(3,086	)		(924	)
Residential Alt-A
Principal deferral			10			1,900			1,880			(20	)		—
Combination of concession types			19			2,826			3,148			322			(790	)
Consumer:
Home equity lines and loans
Principal deferral			10			859			861			2			—
Interest rate reduction			1			99			99			—			(8	)
Other			1			106			106			—			—
Combination of concession types			28			2,190			2,190			—			(270	)
Automobile
Principal deferral			460			6,148			6,148			—			—
Interest rate reduction			15			235			235			—			(22	)
Other			78			339			339			—			—
Combination of concession types			225			2,552			2,552			—			(191	)
Other
Principal deferral			36			332			332			—			—
Interest rate reduction			1			12			12			—			(2	)
Other			2			14			14			—			—
Combination of concession types			120			4,248			4,248			—			(1,187	)
Total			1,258		$	258,075		$	254,352		$	(3,723	)	$	(4,691	)
(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages.
(b)	Represents the present value of interest rate concessions discounted at the effective rate of the original loan.
The table below summarizes the Company’s loan modification activities that were considered troubled debt restructurings for the year ended December 31, 2012:
					Recorded Investment						Financial Effects of
											Modification
		Number			Pre-			Post-			Recorded			Interest
					modifica-			modifica-			Investment			(b)
					tion			tion			(a)
		(Dollars in thousands)
Commercial, financial, leasing, etc.
Principal deferral			61		$	23,888		$	22,456		$	(1,432	)	$	—
Other			3			2,967			3,052			85			—
Combination of concession types			5			628			740			112			(102	)
Real estate:
Commercial
Principal deferral			24			22,855			23,059			204			—
Interest rate reduction			2			665			708			43			(129	)
Combination of concession types			7			1,637			1,656			19			(351	)
Residential builder and developer
Principal deferral			23			36,868			34,740			(2,128	)		—
Combination of concession types			7			37,602			36,148			(1,454	)		—
Other commercial construction
Principal deferral			6			81,062			79,312			(1,750	)		—
Residential
Principal deferral			36			4,643			4,808			165			—
Interest rate reduction			1			109			109			—			(20	)
Combination of concession types			62			12,886			13,146			260			(657	)
Residential Alt-A
Principal deferral			7			968			989			21			—
Combination of concession types			38			8,525			8,717			192			(159	)
Consumer:
Home equity lines and loans
Principal deferral			15			1,285			1,285			—			—
Interest rate reduction			1			144			144			—			(6	)
Combination of concession types			29			2,332			2,332			—			(368	)
Automobile
Principal deferral			618			8,347			8,347			—			—
Interest rate reduction			22			328			328			—			(24	)
Other			67			300			300			—			—
Combination of concession types			375			5,857			5,857			—			(684	)
Other
Principal deferral			80			1,201			1,201			—			—
Interest rate reduction			22			515			515			—			(85	)
Other			13			54			54			—			—
Combination of concession types			84			1,015			1,015			—			(268	)
Total			1,608		$	256,681		$	251,018		$	(5,663	)	$	(2,853	)
(a)	Financial effects impacting the recorded investment included principal payments or advances, charge-offs and capitalized escrow arrearages.
(b)	Represents the present value of interest rate concessions discounted at the effective rate of the original loan.
Summary of Lease Financing Receivables	A summary of lease financing receivables follows:
			December 31
			2014			2013
			(In thousands)
	Commercial leases:
	Direct financings:
	Lease payments receivable		$	1,022,133		$	1,052,214
	Estimated residual value of leased assets			79,525			85,595
	Unearned income			(103,777	)		(114,101	)
	Investment in direct financings			997,881			1,023,708
	Leveraged leases:
	Lease payments receivable			102,457			127,821
	Estimated residual value of leased assets			133,089			133,298
	Unearned income			(44,288	)		(47,188	)
	Investment in leveraged leases			191,258			213,931
	Total investment in leases		$	1,189,139		$	1,237,639
	Deferred taxes payable arising from leveraged leases		$	169,101		$	172,296
Minimum Future Lease Payments to be Received from Lease Financings	At December 31, 2014, the minimum future lease payments to be received from lease financings were as follows:
			(In thousands)
	Year ending December 31:
	2015		$	268,086
	2016			242,248
	2017			177,539
	2018			127,985
	2019			92,205
	Later years			216,527
			$	1,124,590

Allowance_for_credit_losses_Ta

Allowance for credit losses (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Changes in Allowance for Credit Losses	Changes in the allowance for credit losses for the years ended December 31, 2014, 2013 and 2012 were as follows:
		Commercial,			Real Estate
		Financial,
	2014	Leasing, etc.			Commercial			Residential			Consumer			Unallocated		Total
		(In thousands)
	Beginning balance	$	273,383		$	324,978		$	78,656		$	164,644		$	75,015	$	916,676
	Provision for credit losses		51,410			(13,779	)		(3,974	)		89,704			639		124,000
	Net charge-offs
	Charge-offs		(58,943	)		(14,058	)		(21,351	)		(84,390	)		—		(178,742	)
	Recoveries		22,188			10,786			8,579			16,075			—		57,628
	Net charge-offs		(36,755	)		(3,272	)		(12,772	)		(68,315	)		—		(121,114	)
	Ending balance	$	288,038		$	307,927		$	61,910		$	186,033		$	75,654	$	919,562
	2013
	Beginning balance	$	246,759		$	337,101		$	88,807		$	179,418		$	73,775	$	925,860
	Provision for credit losses		124,180			275			3,149			56,156			1,240		185,000
	Allowance related to loans sold or securitized		—			—			—			(11,000	)		—		(11,000	)
	Net charge-offs
	Charge-offs		(109,329	)		(34,595	)		(23,621	)		(85,965	)		—		(253,510	)
	Recoveries		11,773			22,197			10,321			26,035			—		70,326
	Net charge-offs		(97,556	)		(12,398	)		(13,300	)		(59,930	)		—		(183,184	)
	Ending balance	$	273,383		$	324,978		$	78,656		$	164,644		$	75,015	$	916,676
	2012
	Beginning balance	$	234,022		$	367,637		$	91,915		$	143,121		$	71,595	$	908,290
	Provision for credit losses		42,510			5,211			34,864			119,235			2,180		204,000
	Net charge-offs
	Charge-offs		(41,148	)		(41,945	)		(44,314	)		(103,348	)		—		(230,755	)
	Recoveries		11,375			6,198			6,342			20,410			—		44,325
	Net charge-offs		(29,773	)		(35,747	)		(37,972	)		(82,938	)		—		(186,430	)
	Ending balance	$	246,759		$	337,101		$	88,807		$	179,418		$	73,775	$	925,860
Impaired Loans and Leases	The following tables provide information with respect to loans and leases that were considered impaired as of December 31, 2014 and 2013 and for the years ended December 31, 2014, 2013 and 2012.
		December 31, 2014									December 31, 2013
		Recorded			Unpaid			Related			Recorded			Unpaid		Related
		Investment			Principal			Allowance			Investment			Principal		Allowance
					Balance									Balance
		(In thousands)
	With an allowance recorded:
	Commercial, financial, leasing, etc.	$	132,340		$	165,146		$	31,779		$	90,293		$	112,092	$	24,614
	Real estate:
	Commercial		83,955			96,209			14,121			113,570			132,325		19,520
	Residential builder and developer		17,632			22,044			805			33,311			55,122		4,379
	Other commercial construction		5,480			6,484			900			86,260			90,515		4,022
	Residential		88,970			107,343			4,296			96,508			114,521		7,146
	Residential Alt-A		101,137			114,565			11,000			111,911			124,528		14,000
	Consumer:
	Home equity lines and loans		19,771			20,806			6,213			13,672			14,796		3,312
	Automobile		30,317			30,317			8,070			40,441			40,441		11,074
	Other		18,973			18,973			5,459			17,660			17,660		4,541
			498,575			581,887			82,643			603,626			702,000		92,608
	With no related allowance recorded:
	Commercial, financial, leasing, etc.		73,978			81,493			—			28,093			33,095		—
	Real estate:
	Commercial		66,777			78,943			—			65,271			84,333		—
	Residential builder and developer		58,820			96,722			—			72,366			104,768		—
	Other commercial construction		20,738			41,035			—			7,369			11,493		—
	Residential		16,815			26,750			—			84,144			95,358		—
	Residential Alt-A		26,752			46,964			—			28,357			52,211		—
			263,880			371,907			—			285,600			381,258		—
	Total:
	Commercial, financial, leasing, etc.		206,318			246,639			31,779			118,386			145,187		24,614
	Real estate:
	Commercial		150,732			175,152			14,121			178,841			216,658		19,520
	Residential builder and developer		76,452			118,766			805			105,677			159,890		4,379
	Other commercial construction		26,218			47,519			900			93,629			102,008		4,022
	Residential		105,785			134,093			4,296			180,652			209,879		7,146
	Residential Alt-A		127,889			161,529			11,000			140,268			176,739		14,000
	Consumer:
	Home equity lines and loans		19,771			20,806			6,213			13,672			14,796		3,312
	Automobile		30,317			30,317			8,070			40,441			40,441		11,074
	Other		18,973			18,973			5,459			17,660			17,660		4,541
	Total	$	762,455		$	953,794		$	82,643		$	889,226		$	1,083,258	$	92,608
Interest Income Recognized on Loans	Year Ended									Year Ended
	December 31, 2014									December 31, 2013
		Average			Interest Income						Average			Interest Income
		Recorded			Recognized						Recorded			Recognized
		Investment			Total			Cash			Investment			Total		Cash
								Basis								Basis
		(In thousands)
	Commercial, financial, leasing, etc.	$	181,932		$	2,251		$	2,251		$	155,188		$	7,197	$	7,197
	Real estate:
	Commercial		184,773			4,029			4,029			197,533			4,852		4,852
	Residential builder and developer		91,149			142			142			147,288			1,043		796
	Other commercial construction		62,734			1,893			1,893			96,475			5,248		5,248
	Residential		126,005			9,180			6,978			183,059			6,203		4,111
	Residential Alt-A		133,800			6,613			2,546			149,461			6,784		2,341
	Consumer:
	Home equity lines and loans		18,083			750			248			12,811			683		183
	Automobile		35,173			2,251			295			44,116			2,916		515
	Other		18,378			690			191			15,710			634		208
	Total	$	852,027		$	27,799		$	18,573		$	1,001,641		$	35,560	$	25,451
		Year Ended
		December 31, 2012
					Interest Income
					Recognized
		Average			Total			Cash
		Recorded						Basis
		Investment
		(In thousands)
	Commercial, financial, leasing, etc.	$	151,314		$	2,938		$	2,938
	Real estate:
	Commercial		185,171			2,834			2,834
	Residential builder and developer		249,191			1,563			1,102
	Other commercial construction		99,672			5,020			5,020
	Residential		132,888			5,284			3,300
	Residential Alt-A		171,546			7,175			2,226
	Consumer:
	Home equity lines and loans		11,322			663			179
	Automobile		51,650			3,470			724
	Other		11,028			472			197
	Total	$	1,063,782		$	29,419		$	18,520
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,			Commercial			Residential			Other
		Financial,						Builder and			Commercial
		Leasing, etc						Developer			Construction
		(In thousands)
	December 31, 2014
	Pass	$	18,695,440		$	21,837,022		$	1,347,778		$	3,347,522
	Criticized accrual		588,407			578,317			45,845			172,269
	Criticized nonaccrual		177,445			141,600			71,517			25,699
	Total	$	19,461,292		$	22,556,939		$	1,465,140		$	3,545,490
	December 31, 2013
	Pass	$	17,894,592		$	20,972,257		$	1,107,144		$	3,040,106
	Criticized accrual		699,885			596,553			72,941			54,464
	Criticized nonaccrual		110,739			173,048			96,427			35,268
	Total	$	18,705,216		$	21,741,858		$	1,276,512		$	3,129,838
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,			Real Estate
		Financial,
		Leasing, etc.			Commercial			Residential			Consumer			Total
		(In thousands)
	December 31, 2014
	Individually evaluated for impairment	$	31,779		$	15,490		$	14,703		$	19,742		$	81,714
	Collectively evaluated for impairment		251,607			291,244			45,061			165,140			753,052
	Purchased impaired		4,652			1,193			2,146			1,151			9,142
	Allocated	$	288,038		$	307,927		$	61,910		$	186,033			843,908
	Unallocated														75,654
	Total													$	919,562
	December 31, 2013
	Individually evaluated for impairment	$	24,614		$	27,563		$	21,127		$	18,927		$	92,231
	Collectively evaluated for impairment		246,096			296,781			55,864			144,210			742,951
	Purchased impaired		2,673			634			1,665			1,507			6,479
	Allocated	$	273,383		$	324,978		$	78,656		$	164,644			841,661
	Unallocated														75,015
	Total													$	916,676
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,			Real Estate
		Financial,
		Leasing, etc.			Commercial			Residential			Consumer			Total
		(In thousands)
	December 31, 2014
	Individually evaluated for impairment	$	206,318		$	252,347		$	232,398		$	69,061		$	760,124
	Collectively evaluated for impairment		19,244,674			27,148,382			8,406,680			10,911,359			65,711,095
	Purchased impaired		10,300			166,840			18,223			2,374			197,737
	Total	$	19,461,292		$	27,567,569		$	8,657,301		$	10,982,794		$	66,668,956
	December 31, 2013
	Individually evaluated for impairment	$	118,386		$	376,339		$	320,360		$	71,773		$	886,858
	Collectively evaluated for impairment		18,571,124			25,488,584			8,578,677			10,217,124			62,855,509
	Purchased impaired		15,706			283,285			29,184			2,617			330,792
	Total	$	18,705,216		$	26,148,208		$	8,928,221		$	10,291,514		$	64,073,159

Premises_and_equipment_Tables

Premises and equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Summary of Premises and Equipment	The detail of premises and equipment was as follows:
		December 31
		2014		2013
		(In thousands)
	Land	$	82,335	$	84,220
	Buildings — owned		406,522		402,065
	Buildings — capital leases		1,131		1,131
	Leasehold improvements		219,152		208,947
	Furniture and equipment — owned		586,429		547,824
	Furniture and equipment — capital leases		18,853		17,703
			1,314,422		1,261,890
	Less: accumulated depreciation and amortization
	Owned assets		686,372		617,228
	Capital leases		15,066		11,142
			701,438		628,370
	Premises and equipment, net	$	612,984	$	633,520

Capitalized_servicing_assets_T

Capitalized servicing assets (Tables)	12 Months Ended
	Dec. 31, 2014
Transfers and Servicing [Abstract]
Servicing Asset at Amortized Cost	Changes in capitalized servicing assets were as follows:
		Residential Mortgage Loans									Commercial Mortgage Loans
	For Year Ended December 31,	2014			2013			2012			2014			2013			2012
		(In thousands)
	Beginning balance	$	126,377		$	104,855		$	131,264		$	72,499		$	59,978		$	51,250
	Originations		28,285			52,375			14,577			15,922			26,754			19,653
	Purchases		289			272			109			730			—			—
	Recognized in loan securitization transactions		—			13,696			—			—			—			—
	Amortization		(45,080	)		(44,821	)		(41,095	)		(16,212	)		(14,233	)		(10,925	)
			109,871			126,377			104,855			72,939			72,499			59,978
	Valuation allowance		—			(300	)		(4,500	)		—			—			—
	Ending balance, net	$	109,871		$	126,077		$	100,355		$	72,939		$	72,499		$	59,978
		Other									Total
	For Year Ended December 31,	2014			2013			2012			2014			2013			2012
		(In thousands)
	Beginning balance	$	11,225		$	8,143		$	15,678		$	210,101		$	172,976		$	198,192
	Originations		—			—			—			44,207			79,129			34,230
	Purchases		—			—			—			1,019			272			109
	Recognized in loan securitization transactions		—			9,382			—			—			23,078			—
	Amortization		(7,118	)		(6,300	)		(7,535	)		(68,410	)		(65,354	)		(59,555	)
			4,107			11,225			8,143			186,917			210,101			172,976
	Valuation allowance		—			—			—			—			(300	)		(4,500	)
	Ending balance, net	$	4,107		$	11,225		$	8,143		$	186,917		$	209,801		$	168,476
Economic Assumptions Used to Determine Fair Value of Capitalized Servicing Rights and Sensitivity of Value to Changes in Assumptions
		Residential			Commercial
	Weighted-average prepayment speeds		11.22	%
	Impact on fair value of 10% adverse change	$	(8,001,000	)
	Impact on fair value of 20% adverse change		(15,364,000	)
	Weighted-average OAS		10.65	%
	Impact on fair value of 10% adverse change	$	(6,959,000	)
	Impact on fair value of 20% adverse change		(13,492,000	)
	Weighted-average discount rate					18	%
	Impact on fair value of 10% adverse change				$	(3,671,000	)
	Impact on fair value of 20% adverse change					(7,092,000	)

Goodwill_and_other_intangible_1

Goodwill and other intangible assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets	Total amortizing intangible assets were comprised of the following:
		Gross Carrying		Accumulated		Net Carrying
		Amount		Amortization		Amount
		(In thousands)
	December 31, 2014
	Core deposit	$	755,794	$	730,188	$	25,606
	Other		177,268		167,847		9,421
	Total	$	933,062	$	898,035	$	35,027
	December 31, 2013
	Core deposit	$	755,794	$	705,518	$	50,276
	Other		177,268		158,693		18,575
	Total	$	933,062	$	864,211	$	68,851
Estimated Amortization Expense in Future Years	Estimated amortization expense in future years for such intangible assets is as follows:
		(In thousands)
	Year ending December 31:
	2015	$	20,938
	2016		10,052
	2017		3,303
	2018		734
		$	35,027
Summary of Goodwill Assigned to Reportable Segments for Purposes of Testing for Impairment	A summary of goodwill assigned to each of the Company’s reportable segments as of December 31, 2014 and 2013 for purposes of testing for impairment is as follows.
		(In thousands)
	Business Banking	$	748,907
	Commercial Banking		907,524
	Commercial Real Estate		349,197
	Discretionary Portfolio		—
	Residential Mortgage Banking		—
	Retail Banking		1,144,404
	All Other		374,593
	Total	$	3,524,625

Borrowings_Tables

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Amounts and Interest Rates of Short-term Borrowings	The amounts and interest rates of short-term borrowings were as follows:
		Federal Funds			Other			Total
		Purchased			Short-term
		and			Borrowings
		Repurchase
		Agreements
		(Dollars in thousands)
	At December 31, 2014
	Amount outstanding	$	192,676			—		$	192,676
	Weighted-average interest rate		0.07	%		—			0.07	%
	For the year ended December 31, 2014
	Highest amount at a month-end	$	280,350			—
	Daily-average amount outstanding		214,736			—		$	214,736
	Weighted-average interest rate		0.05	%		—			0.05	%
	At December 31, 2013
	Amount outstanding	$	260,455			—		$	260,455
	Weighted-average interest rate		0.04	%		—			0.04	%
	For the year ended December 31, 2013
	Highest amount at a month-end	$	563,879			—
	Daily-average amount outstanding		390,034			—		$	390,034
	Weighted-average interest rate		0.11	%		—			0.11	%
	At December 31, 2012
	Amount outstanding	$	1,074,482			—		$	1,074,482
	Weighted-average interest rate		0.11	%		—			0.11	%
	For the year ended December 31, 2012
	Highest amount at a month-end	$	1,224,194		$	50,016
	Daily-average amount outstanding		822,859			16,043		$	838,902
	Weighted-average interest rate		0.15	%		0.57	%		0.15	%
Lines of Credit Under Formal Agreements	At December 31, 2014, the Company had lines of credit under formal agreements as follows:
		M&T Bank			Wilmington
					Trust,  N.A.
		(In thousands)
	Outstanding borrowings	$	1,161,475		$	—
	Unused		19,825,036			275,414
Long-term Borrowings	Long-term borrowings were as follows:
		December 31,
		2014			2013
		(In thousands)
	Senior notes of M&T Bank:
	Variable rate due 2016	$	300,000		$	300,000
	Variable rate due 2017		550,000			—
	1.25% due 2017		499,969			—
	1.40% due 2017		749,756			—
	1.45% due 2018		503,118			502,479
	2.25% due 2019		648,243			—
	2.30% due 2019		748,965			—
	Advances from FHLB:
	Fixed rates		1,161,514			29,079
	Agreements to repurchase securities		1,400,000			1,400,000
	Subordinated notes of Wilmington Trust Corporation
	(a wholly owned subsidiary of M&T):
	8.50% due 2018		218,883			224,067
	Subordinated notes of M&T Bank:
	6.625% due 2017		428,627			437,582
	9.50% due 2018		—			50,000
	5.585% due 2020, variable rate commencing 2015		400,846			392,964
	5.629% due 2021, variable rate commencing 2016		538,961			559,378
	Junior subordinated debentures of M&T associated with preferred capital securities:
	Fixed rates:
	M&T Capital Trust I — 8.234%, due 2027		154,640			154,640
	M&T Capital Trust II — 8.277%, due 2027		103,093			103,093
	M&T Capital Trust III — 9.25%, due 2027		65,784			66,109
	BSB Capital Trust I — 8.125%, due 2028		15,612			15,589
	Provident Trust I — 8.29%, due 2028		25,405			25,051
	Southern Financial Statutory Trust I — 10.60%, due 2030		6,550			6,521
	M&T Capital Trust IV — 8.50%, due 2068		—			350,010
	Variable rates:
	First Maryland Capital I — due 2027		145,179			144,641
	First Maryland Capital II — due 2027		146,627			145,964
	Allfirst Asset Trust — due 2029		96,204			96,059
	BSB Capital Trust III — due 2033		15,464			15,464
	Provident Trust III — due 2033		52,692			52,176
	Southern Financial Capital Trust III — due 2033		7,816			7,747
	Other		23,011			30,257
		$	9,006,959		$	5,108,870
Maturity of Long-term Borrowings	Long-term borrowings at December 31, 2014 mature as follows:
		(In thousands)
	Year ending December 31:
	2015	$	6,444
	2016		1,105,540
	2017		3,407,786
	2018		723,516
	2019		1,971,842
	Later years		1,791,831
		$	9,006,959

Shareholders_equity_Tables

Shareholders' equity (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Issued and Outstanding Preferred Stock	Issued and outstanding preferred stock of M&T is presented below:
			December 31, 2014				December 31, 2013
			Shares		Carrying		Shares		Carrying
			Issued and		Value		Issued and		Value
			Outstanding				Outstanding
			(Dollars in thousands)
	Series A(a)
	Fixed Rate Cumulative Perpetual Preferred Stock, Series A, $1,000 liquidation preference per share			230,000	$	230,000		230,000	$	230,000
	Series C(a)
	Fixed Rate Cumulative Perpetual Preferred Stock, Series C, $1,000 liquidation preference per share			151,500		151,500		151,500		151,500
	Series D(b)
	Fixed Rate Non-cumulative Perpetual Preferred Stock, Series D, $10,000 liquidation preference per share			50,000		500,000		50,000		500,000
	Series E(c)
	Fixed-to-Floating Rate Non-cumulative Perpetual Preferred Stock, Series E, $1,000 liquidation preference per share			350,000		350,000		—		—
	(a)	Dividends, if declared, were paid quarterly at a rate of 5% per year through November 14, 2013 and are paid at 6.375% thereafter. Warrants to purchase M&T common stock were issued in connection with the Series A and C preferred stock (Series A — 1,218,522 common shares at $73.86 per share; Series C — 407,542 common shares at $55.76 per share). In March 2013, the Series C warrant were exercised in a “cashless” exercise, resulting in the issuance of 186,589 common shares. During 2014 and 2013, 427,905 and 69,127, respectively, of the Series A warrants were exercised in “cashless” exercises, resulting in the issuance of 169,543 and 25,427 common shares. Remaining outstanding Series A warrants were 721,490 at December 31, 2014.
	(b)	Dividends, if declared, will be paid semi-annually at a rate of 6.875% per year. The shares are redeemable in whole or in part on or after June 15, 2016. 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, will be paid semi-annually at a rate of 6.45% through February 14, 2024 and thereafter will be paid quarterly at a rate of the three-month LIBOR plus 361 basis points (hundredths of one percent). The shares are redeemable in whole or in part on or after February 15, 2024. Notwithstanding M&T’s option to redeem the shares, if an event occurs such that the shares no longer qualify as Tier 1 capital, M&T may redeem all of the shares within 90 days following that occurrence.

Stockbased_compensation_plans_

Stock-based compensation plans (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Restricted Stock and Restricted Stock Unit Activity	A summary of restricted stock and restricted stock unit activity follows:
		Restricted			Weighted-		Restricted			Weighted-
		Stock Units			Average		Stock			Average
		Outstanding			Grant Price		Outstanding			Grant Price
	Unvested at January 1, 2014		770,830		$	89.58		862,695		$	87.29
	Granted		299,525			111.53		221,822			111.64
	Vested		(279,747	)		84.95		(295,438	)		81.32
	Cancelled		(1,197	)		103.25		(27,434	)		96.7
	Unvested at December 31, 2014		789,411		$	99.53		761,645		$	96.36
Summary of Stock Option Activity	A summary of stock option activity follows:
		Stock			Weighted-Average					Aggregate
		Options								Intrinsic Value
		Outstanding			Exercise		Life			(In thousands)
					Price		(In Years)
	Outstanding at January 1, 2014		4,880,761		$	105.48
	Granted		200			111.51
	Exercised		(1,372,113	)		101.55
	Expired		(75,978	)		184.15
	Outstanding at December 31, 2014		3,432,870		$	105.31		2.1		$	71,418
	Exercisable at December 31, 2014		3,432,470		$	105.31		2.1		$	71,408

Pension_plans_and_other_postre1

Pension plans and other postretirement benefits (Tables)	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Net Periodic Pension Expense for Defined Benefit Plans	Net periodic pension expense for defined benefit plans consisted of the following:
			Year Ended December 31
			2014			2013			2012
			(In thousands)
	Service cost		$	20,520		$	24,360		$	29,549
	Interest cost on benefit obligation			69,162			60,130			62,037
	Expected return on plan assets			(91,568	)		(87,353	)		(70,511	)
	Amortization of prior service credit			(6,552	)		(6,556	)		(6,559	)
	Recognized net actuarial loss			14,494			41,076			37,386
	Net periodic pension expense		$	6,056		$	31,657		$	51,902
	Net other postretirement benefits expense for defined benefit plans consisted of the following:
			Year Ended December 31
			2014			2013			2012
			(In thousands)
	Service cost		$	605		$	742		$	668
	Interest cost on benefit obligation			2,778			2,691			3,737
	Amortization of prior service cost (credit)			(1,359	)		(1,359	)		21
	Recognized net actuarial loss			—			360			530
	Net other postretirement benefits expense		$	2,024		$	2,434		$	4,956
Data Relating to Funding Position of Defined Benefit Plans	Data relating to the funding position of the defined benefit plans were as follows:
			Pension Benefits						Other
									Postretirement Benefits
			2014			2013			2014			2013
			(In thousands)
	Change in benefit obligation:
	Benefit obligation at beginning of year		$	1,484,193		$	1,644,567		$	60,592		$	74,966
	Service cost			20,520			24,360			605			742
	Interest cost			69,162			60,130			2,778			2,691
	Plan participants’ contributions			—			—			3,498			3,069
	Amendments			4,619			—			—			—
	Actuarial (gain) loss			300,444			(184,181	)		7,793			(12,830	)
	Medicare Part D reimbursement			—			—			495			509
	Benefits paid			(65,529	)		(60,683	)		(8,259	)		(8,555	)
	Benefit obligation at end of year			1,813,409			1,484,193			67,502			60,592
	Change in plan assets:
	Fair value of plan assets at beginning of year			1,506,684			1,408,771			—			—
	Actual return on plan assets			56,430			150,795			—			—
	Employer contributions			8,076			7,801			4,266			4,977
	Plan participants’ contributions			—			—			3,498			3,069
	Medicare Part D reimbursement			—			—			495			509
	Benefits and other payments			(65,529	)		(60,683	)		(8,259	)		(8,555	)
	Fair value of plan assets at end of year			1,505,661			1,506,684			—			—
	Funded status		$	(307,748	)	$	22,491		$	(67,502	)	$	(60,592	)
	Assets and liabilities recognized in the consolidated balance sheet were:
	Net prepaid asset		$	—		$	139,576		$	—		$	—
	Accrued liabilities			(307,748	)		(117,085	)		(67,502	)		(60,592	)
	Amounts recognized in accumulated other comprehensive income (“AOCI”) were:
	Net loss (gain)		$	512,473		$	191,386		$	6,737		$	(1,056	)
	Net prior service cost			(5,728	)		(16,899	)		(10,455	)		(11,814	)
	Pre-tax adjustment to AOCI			506,745			174,487			(3,718	)		(12,870	)
	Taxes.			(198,897	)		(68,486	)		1,459			5,051
	Net adjustment to AOCI.		$	307,848		$	106,001		$	(2,259	)	$	(7,819	)
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income	The table below reflects the changes in plan assets and benefit obligations recognized in other comprehensive income related to the Company’s postretirement benefit plans.
			Pension Plans			Other			Total
						Postretirement
						Benefit Plans
			(In thousands)
	2014
	Net loss		$	335,581		$	7,793		$	343,374
	Prior service cost			4,619			—			4,619
	Amortization of prior service credit			6,552			1,359			7,911
	Amortization of loss			(14,494	)		—			(14,494	)
	Total recognized in other comprehensive income, pre-tax		$	332,258		$	9,152		$	341,410
	2013
	Net gain		$	(247,622	)	$	(12,830	)	$	(260,452	)
	Amortization of prior service credit			6,556			1,359			7,915
	Amortization of loss			(41,076	)		(360	)		(41,436	)
	Total recognized in other comprehensive income, pre-tax		$	(282,142	)	$	(11,831	)	$	(293,973	)
Amortization of Amounts in Accumulated Other Comprehensive Income Expected to be Recognized as Components of Net Periodic Benefit Expense	The following table reflects the amortization of amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit expense during 2015:
			Pension Plans			Other
						Postretirement
						Benefit Plans
			(In thousands)
	Amortization of net prior service credit		$	(6,005	)	$	(1,359	)
	Amortization of net loss			44,653			91
Assumed Weighted-Average Rates Used to Determine Benefit Obligations	The assumed weighted-average rates used to determine benefit obligations at December 31 were:
			Pension						Other
			Benefits						Postretirement
									Benefits
			2014			2013			2014			2013
	Discount rate			4	%		4.75	%		4	%		4.75	%
	Rate of increase in future compensation levels			4.39	%		4.42	%		—			—
Assumed Weighted-Average Rates Used to Determine Net Benefit Expense	The assumed weighted-average rates used to determine net benefit expense for the years ended December 31 were:
			Pension Benefits									Other
												Postretirement Benefits
			2014			2013			2012			2014			2013			2012
	Discount rate			4.75	%		3.75	%		4.25	%		4.75	%		3.75	%		4.25	%
	Long-term rate of return on plan assets			6.5	%		6.5	%		6.5	%		—			—			—
	Rate of increase in future compensation levels			4.42	%		4.5	%		4.5	%		—			—			—
Effects on One-Percentage Point Change in Assumed Health Care Cost Trend Rates	A one-percentage point change in assumed health care cost trend rates would have had the following effects:
			1%			-1%
			(In thousands)
	Increase (decrease) in:
	Service and interest cost		$	97		$	(88	)
	Accumulated postretirement benefit obligation			3,005			(2,678	)
Fair Values of Company's Pension Plan Assets by Asset Category	The fair values of the Company’s pension plan assets at December 31, 2014, by asset category, were as follows:
			Fair Value Measurement of Plan Assets At December 31, 2014
			Total			Quoted Prices			Significant			Significant
						in Active			Observable			Unobservable
						Markets			Inputs			Inputs
						for Identical Assets			(Level 2)			(Level 3)
						(Level 1)
			(In thousands)
	Asset category:
	Money-market funds		$	29,458		$	29,458		$	—		$	—
	Equity securities:
	M&T			154,252			154,252			—			—
	Domestic(a)			214,127			214,127			—			—
	International(b)			16,170			16,170			—			—
	Mutual funds:
	Domestic(a)			305,817			305,817			—			—
	International(b)			381,101			381,101			—			—
				1,071,467			1,071,467			—			—
	Debt securities:
	Corporate(c)			102,848			—			102,848			—
	Government			92,772			—			92,772			—
	International			7,196			—			7,196			—
	Mutual funds:
	Domestic(d)			27,847			27,847			—			—
				230,663			27,847			202,816			—
	Other:
	Diversified mutual fund			96,936			96,936			—			—
	Private real estate			2,162			—			—			2,162
	Private equity			6,234			—			—			6,234
	Hedge funds			66,694			42,430			—			24,264
				172,026			139,366			—			32,660
	Total(e)		$	1,503,614		$	1,268,138		$	202,816		$	32,660
	The fair values of the Company’s pension plan assets at December 31, 2013, by asset category, were as follows:
			Fair Value Measurement of Plan Assets At December 31, 2013
			Total			Quoted Prices			Significant			Significant
						in Active			Observable			Unobservable
						Markets			Inputs			Inputs
						for Identical Assets			(Level 2)			(Level 3)
						(Level 1)
			(In thousands)
	Asset category:
	Money-market funds		$	37,952		$	37,952		$	—		$	—
	Equity securities:
	M&T			142,955			142,955			—			—
	Domestic(a)			271,203			271,203			—			—
	International(b)			24,053			24,053			—			—
	Mutual funds:
	Domestic(a)			194,099			194,099			—			—
	International(b)			413,685			413,685			—			—
				1,045,995			1,045,995			—			—
	Debt securities:
	Corporate(c)			63,196			—			63,196			—
	Government			75,043			—			75,043			—
	International			2,443			—			2,443			—
	Mutual funds:
	Domestic(d)			68,280			68,280			—			—
	International			43,742			43,742			—			—
				252,704			112,022			140,682			—
	Other:
	Diversified mutual fund			93,055			93,055			—			—
	Private real estate			3,123			—			—			3,123
	Private equity			6,199			—			—			6,199
	Hedge funds			65,663			41,489			—			24,174
				168,040			134,544			—			33,496
Total(e)		$	1,504,691		$	1,330,513		$	140,682		$	33,496
(a)	This category is comprised of equities of companies primarily within the mid-cap and large-cap sectors of the U.S. economy and range across diverse industries.
(b)	This category is comprised of equities in companies primarily within the mid-cap and large-cap sectors of international markets mainly in developed markets in Europe and the Pacific Rim.
(c)	This category represents investment grade bonds of U.S. issuers from diverse industries.
(d)	Approximately 55% of the mutual funds were invested in investment grade bonds of U.S. issuers and 45% in high-yielding bonds at December 31, 2014. Approximately 35% of the mutual funds were invested in investment grade bonds of U.S. issuers and 65% in high-yielding bonds at December 31, 2013. The holdings within the funds were spread across diverse industries.
(e)	Excludes dividends and interest receivable totaling $2,047,000 and $1,993,000 at December 31, 2014 and 2013, respectively.
Changes in Level 3 Pension Plan Assets Measured at Fair Value on Recurring Basis	The changes in Level 3 pension plan assets measured at estimated fair value on a recurring basis during the year ended December 31, 2014 were as follows:
			Balance –			Sales			Total			Balance –
			January 1,						Realized/			December 31,
			2014						Unrealized			2014
									Gains
			(In thousands)
	Other
	Private real estate		$	3,123		$	(1,167	)	$	206		$	2,162
	Private equity			6,199			(905	)		940			6,234
	Hedge funds			24,174			(513	)		603			24,264
	Total		$	33,496		$	(2,585	)	$	1,749		$	32,660
Defined Benefit Plan Estimated Future Benefit Payments	Estimated benefits expected to be paid in future years related to the Company’s defined benefit pension and other postretirement benefits plans are as follows:
			Pension			Other
			Benefits			Postretirement
						Benefits
			(In thousands)
	Year ending December 31:
	2015		$	70,107		$	5,830
	2016			73,169			5,719
	2017			77,294			5,554
	2018			81,231			5,412
	2019			87,027			5,281
	2020 through 2024			497,177			24,190

Income_taxes_Tables

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Components of Income Tax Expense	The components of income tax expense were as follows:
		Year Ended December 31
		2014			2013			2012
		(In thousands)
	Current
	Federal	$	378,978		$	371,249		$	309,156
	State and city		50,790			68,035			82,014
	Total current		429,768			439,284			391,170
	Deferred
	Federal		65,503			106,537			117,229
	State and city		27,345			33,248			14,629
	Total deferred		92,848			139,785			131,858
	Total income taxes applicable to pre-tax income	$	522,616		$	579,069		$	523,028
Schedule of Income Tax Expense Benefit Reconciliation	Total income taxes differed from the amount computed by applying the statutory federal income tax rate to pre-tax income as follows:
		Year Ended December 31
		2014			2013			2012
		(In thousands)
	Income taxes at statutory federal income tax rate	$	556,102		$	601,142		$	543,384
	Increase (decrease) in taxes:
	Tax-exempt income		(31,752	)		(34,747	)		(33,890	)
	State and city income taxes, net of federal income tax effect		50,788			65,834			62,818
	Low income housing and other credits		(49,526	)		(49,206	)		(42,074	)
	Other		(2,996	)		(3,954	)		(7,210	)
		$	522,616		$	579,069		$	523,028
Deferred Tax Assets (Liabilities)	Deferred tax assets (liabilities) were comprised of the following at December 31:
		2014			2013			2012
		(In thousands)
	Losses on loans and other assets	$	605,273		$	645,713		$	809,033
	Postretirement and other employee benefits		34,052			30,023			34,517
	Incentive compensation plans		36,450			37,772			50,067
	Interest on loans		79,147			100,725			72,278
	Retirement benefits		120,222			—			91,980
	Stock-based compensation		64,017			63,101			69,874
	Depreciation and amortization		3,527			1,404			12,130
	Other		100,999			121,561			103,027
	Gross deferred tax assets		1,043,687			1,000,299			1,242,906
	Leasing transactions		(280,596	)		(284,370	)		(291,524	)
	Unrealized investment gains		(82,065	)		(21,779	)		(23,574	)
	Capitalized servicing rights		(46,393	)		(46,041	)		(20,348	)
	Interest on subordinated note exchange		(3,125	)		(6,075	)		(8,794	)
	Retirement benefits		—			(9,397	)		—
	Other		(63,814	)		(49,450	)		(61,410	)
	Gross deferred tax liabilities		(475,993	)		(417,112	)		(405,650	)
	Net deferred tax asset	$	567,694		$	583,187		$	837,256
Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits follows:
		Federal,			Accrued			Unrecognized
		State and			Interest			Income Tax
		Local Tax						Benefits
		(In thousands)
	Gross unrecognized tax benefits at January 1, 2012	$	18,333		$	9,277		$	27,610
	Increases in unrecognized tax benefits as a result of tax positions taken during 2012		860			—			860
	Increases in unrecognized tax benefits as a result of tax positions taken in prior years		—			4,514			4,514
	Decreases in unrecognized tax benefits as a result of settlements with taxing authorities		(1,002	)		—			(1,002	)
	Decreases in unrecognized tax benefits because applicable returns are no longer subject to examination		(1,643	)		(1,412	)		(3,055	)
	Gross unrecognized tax benefits at December 31, 2012		16,548			12,379			28,927
	Increases in unrecognized tax benefits as a result of tax positions taken during 2013		2,267			—			2,267
	Increases in unrecognized tax benefits as a result of tax positions taken in prior years		—			4,429			4,429
	Decreases in unrecognized tax benefits as a result of settlements with taxing authorities		(1,854	)		(487	)		(2,341	)
	Decreases in unrecognized tax benefits because applicable returns are no longer subject to examination		(2,350	)		(1,625	)		(3,975	)
	Gross unrecognized tax benefits at December 31, 2013		14,611			14,696			29,307
	Increases in unrecognized tax benefits as a result of tax positions taken during 2014		769			—			769
	Increases in unrecognized tax benefits as a result of tax positions taken in prior years		—			453			453
	Decreases in unrecognized tax benefits as a result of settlements with taxing authorities		(4,668	)		(11,280	)		(15,948	)
	Gross unrecognized tax benefits at December 31, 2014	$	10,712		$	3,869			14,581
	Less: Federal, state and local income tax benefits								(5,103	)
	Net unrecognized tax benefits at December 31, 2014 that, if recognized, would impact the effective income tax rate							$	9,478

Earnings_per_common_share_Tabl

Earnings per common share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Computations of Basic Earnings Per Common Share	The computations of basic earnings per common share follow:
			Year Ended December 31
			2014			2013			2012
			(In thousands, except per share)
	Income available to common shareholders:
	Net income		$	1,066,246		$	1,138,480		$	1,029,498
	Less: Preferred stock dividends(a)			(75,878	)		(54,120	)		(53,450	)
	Amortization of preferred stock discount(a)			—			(7,942	)		(8,026	)
	Net income available to common equity			990,368			1,076,418			968,022
	Less: Income attributable to unvested stock-based compensation awards			(11,837	)		(13,989	)		(14,632	)
	Net income available to common shareholders		$	978,531		$	1,062,429		$	953,390
	Weighted-average shares outstanding:
	Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards			132,532			130,354			127,793
	Less: Unvested stock-based compensation awards			(1,582	)		(1,700	)		(1,929	)
	Weighted-average shares outstanding			130,950			128,654			125,864
	Basic earnings per common share		$	7.47		$	8.26		$	7.57
	(a)	Including impact of not as yet declared cumulative dividends.
Computations of Diluted Earnings Per Common Share	The computations of diluted earnings per common share follow:
			Year Ended December 31
			2014			2013			2012
			(In thousands, except per share)
	Net income available to common equity		$	990,368		$	1,076,418		$	968,022
	Less: Income attributable to unvested stock-based compensation awards			(11,787	)		(13,922	)		(14,593	)
	Net income available to common shareholders		$	978,581		$	1,062,496		$	953,429
	Adjusted weighted-average shares outstanding:
	Common and unvested stock-based compensation awards			132,532			130,354			127,793
	Less: Unvested stock-based compensation awards			(1,582	)		(1,700	)		(1,929	)
	Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock			894			949			541
	Adjusted weighted-average shares outstanding			131,844			129,603			126,405
	Diluted earnings per common share		$	7.42		$	8.2		$	7.54

Comprehensive_income_Tables

Comprehensive income (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income	The following tables display the components of other comprehensive income (loss) and amounts reclassified from accumulated other comprehensive income (loss) to net income.
			Investment Securities						Defined			Other			Total			Income			Net
									Benefit						Amount			Tax
			With			All			Plans						Before Tax
			OTTI			Other
			(In thousands)
	Balance — January 1, 2014		$	37,255			18,450			(161,617	)		115			(105,797	)		41,638		$	(64,159	)
	Other comprehensive income before reclassifications:
	Unrealized holding gains (losses), net			(29,818	)		180,005			—			—			150,187			(58,962	)		91,225
	Foreign currency translation adjustment			—			—			—			(4,039	)		(4,039	)		1,432			(2,607	)
	Unrealized losses on cash flow hedges			—			—			—			(165	)		(165	)		65			(100	)
	Current year benefit plans losses			—			—			(347,993	)		—			(347,993	)		136,587			(211,406	)
	Total other comprehensive income (loss) before reclassifications			(29,818	)		180,005			(347,993	)		(4,204	)		(202,010	)		79,122			(122,888	)
	Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
	Accretion of unrealized holding losses on held-to-maturity (“HTM”) securities			1			3,373			—			—			3,374	(a)		(1,324	)		2,050
	Accretion of losses on terminated cash flow hedges			—			—			—			7			7	(d)		(3	)		4
	Amortization of prior service credit			—			—			(7,911	)		—			(7,911	)(e)		3,105			(4,806	)
	Amortization of actuarial losses			—			—			14,494			—			14,494	(e)		(5,689	)		8,805
	Total reclassifications			1			3,373			6,583			7			9,964			(3,911	)		6,053
	Total gain (loss) during the period			(29,817	)		183,378			(341,410	)		(4,197	)		(192,046	)		75,211			(116,835	)
	Balance — December 31, 2014		$	7,438			201,828			(503,027	)		(4,082	)		(297,843	)		116,849		$	(180,994	)
			Investment Securities						Defined			Other			Total			Income			Net
									Benefit						Amount			Tax
			With			All			Plans						Before Tax
			OTTI			Other
			(In thousands)
	Balance — January 1, 2013		$	(91,835	)		152,199			(455,590	)		(431	)		(395,657	)		155,393		$	(240,264	)
	Other comprehensive income before reclassifications:
	Unrealized holding gains (losses), net			77,794			(129,628	)		—			—			(51,834	)		20,311			(31,523	)
	Foreign currency translation adjustment			—			—			—			546			546			(165	)		381
	Current year benefit plans gains			—			—			260,452			—			260,452			(102,227	)		158,225
	Total other comprehensive income (loss) before reclassifications			77,794			(129,628	)		260,452			546			209,164			(82,081	)		127,083
	Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
	Accretion of unrealized holding losses on HTM securities			279			4,008			—			—			4,287	(a)		(1,683	)		2,604
	OTTI charges recognized in net income			9,800			—			—			—			9,800	(b)		(3,847	)		5,953
	Losses (gains) realized in net income			41,217			(8,129	)		—			—			33,088	(c)		(12,987	)		20,101
	Amortization of prior service credit			—			—			(7,915	)		—			(7,915	)(e)		3,107			(4,808	)
	Amortization of actuarial losses			—			—			41,436			—			41,436	(e)		(16,264	)		25,172
	Total reclassifications			51,296			(4,121	)		33,521			—			80,696			(31,674	)		49,022
	Total gain (loss) during the period			129,090			(133,749	)		293,973			546			289,860			(113,755	)		176,105
	Balance —December 31, 2013		$	37,255			18,450			(161,617	)		115			(105,797	)		41,638		$	(64,159	)
			Investment Securities						Defined			Other			Total			Income			Net
									Benefit						Amount			Tax
			With			All			Plans						Before Tax
			OTTI			Other
			(In thousands)
	Balance — January 1, 2012		$	(138,319	)		9,757			(457,145	)		(1,062	)		(586,769	)		230,328		$	(356,441	)
	Other comprehensive income before reclassifications:
	Unrealized holding gains (losses), net			(2,998	)		137,921			—			—			134,923			(52,905	)		82,018
	Foreign currency translation adjustment			—			—			—			809			809			(290	)		519
	Current year benefit plans losses			—			—			(29,823	)		—			(29,823	)		11,705			(18,118	)
	Total other comprehensive income (loss) before reclassifications			(2,998	)		137,921			(29,823	)		809			105,909			(41,490	)		64,419
	Amounts reclassified from accumulated other comprehensive income that (increase) decrease net income:
	Accretion of unrealized holding losses on HTM securities			1,660			4,530			—			—			6,190	(a)		(2,430	)		3,760
	OTTI charges recognized in net income			47,822			—			—			—			47,822	(b)		(18,770	)		29,052
	Gains realized in net income			—			(9	)		—			—			(9	)(c)		4			(5	)
	Amortization of gains on terminated cash flow hedges			—			—			—			(178	)		(178	)(d)		66			(112	)
	Amortization of prior service credit			—			—			(6,538	)		—			(6,538	)(e)		2,566			(3,972	)
	Amortization of actuarial losses			—			—			37,916			—			37,916	(e)		(14,881	)		23,035
	Total reclassifications			49,482			4,521			31,378			(178	)		85,203			(33,445	)		51,758
	Total gain during the period			46,484			142,442			1,555			631			191,112			(74,935	)		116,177
	Balance —December 31, 2012		$	(91,835	)		152,199			(455,590	)		(431	)		(395,657	)		155,393		$	(240,264	)
	(a)	Included in interest income.
	(b)	Included in OTTI losses recognized in earnings.
(c)	Included in gain (loss) on bank investment securities.
(d)	Included in interest expense.
(e)	Included in salaries and employee benefits expense.
Accumulated Other Comprehensive Income (Loss), Net	Accumulated other comprehensive income (loss), net consisted of unrealized gains (losses) as follows:
			Investment Securities						Defined			Other			Total
									Benefit
			With OTTI			All Other			Plans
									(In thousands)
	Balance at January 1, 2012		$	(84,029	)	$	5,995		$	(277,716	)	$	(691	)	$	(356,441	)
	Net gain (loss) during 2012			28,239			86,586			945			407			116,177
	Balance at December 31, 2012			(55,790	)		92,581			(276,771	)		(284	)		(240,264	)
	Net gain (loss) during 2013			78,422			(81,287	)		178,589			381			176,105
	Balance at December 31, 2013			22,632			11,294			(98,182	)		97			(64,159	)
	Net gain (loss) during 2014			(18,114	)		111,389			(207,407	)		(2,703	)		(116,835	)
	Balance at December 31, 2014		$	4,518		$	122,683		$	(305,589	)	$	(2,606	)	$	(180,994	)

Other_income_and_other_expense1

Other income and other expense (Tables)	12 Months Ended
	Dec. 31, 2014
Other Income and Expenses [Abstract]
Other Income and Other Expense	The following items, which exceeded 1% of total interest income and other income in the respective period, were included in either “other revenues from operations” or “other costs of operations” in the consolidated statement of income:
		Year Ended December 31
		2014		2013		2012
		(In thousands)
	Other income:
	Bank owned life insurance	$	50,004	$	56,120	$	51,199
	Credit-related fee income		72,454		72,271		68,596
	Letter of credit fees		56,708		59,889		58,496
	Gains from loan securitization transactions				63,066
	Other expense:
	Professional services		401,946		335,794		248,544
	Amortization of capitalized servicing rights		68,410		65,354		59,555
	Advertising and promotion				56,597		52,388

Derivative_financial_instrumen1

Derivative financial instruments (Tables)	12 Months Ended
	Dec. 31, 2014
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						Estimated Fair
			Amount			Maturity		Rate						Value Gain
								Fixed			Variable
			(In thousands)			(In years)								(In thousands)
	December 31, 2014
	Fair value hedges:
	Fixed rate long-term borrowings(a)		$	1,400,000			2.7		4.42	%		1.19	%	$	73,251
	December 31, 2013
	Fair value hedges:
	Fixed rate long-term borrowings(a)		$	1,400,000			3.7		4.42	%		1.2	%	$	102,875
	(a)	Under the terms of these agreements, the Company receives settlement amounts at a fixed rate and pays at a variable rate.
Notional Amount of Interest Rate Swap Agreements Outstanding Maturity	The notional amount of interest rate swap agreements entered into for risk management purposes that were outstanding at December 31, 2014 mature as follows:
			(In thousands)
	Year ending December 31:
	2016		$	500,000
	2017			400,000
	2018			500,000
			$	1,400,000
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
			December 31					December 31
			2014			2013		2014			2013
			(In thousands)
	Derivatives designated and qualifying as hedging instruments
	Fair value hedges:
	Interest rate swap agreements(a)		$	73,251		$	102,875	$	—		$	—
	Commitments to sell real estate loans(a)			728			6,957		4,217			487
				73,979			109,832		4,217			487
	Derivatives not designated and qualifying as hedging instruments
	Mortgage-related commitments to originate real estate loans for sale(a)			17,396			7,616		49			3,675
	Commitments to sell real estate loans(a)			754			6,120		4,330			230
	Trading:
	Interest rate contracts(b)			215,614			274,864		173,513			234,455
	Foreign exchange and other option and futures contracts(b)			31,112			15,831		29,950			15,342
				264,876			304,431		207,842			253,702
	Total derivatives		$	338,855		$	414,263	$	212,059		$	254,189
	(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.
Information About Fair Values of Derivative Instruments in Consolidated Statement of Income	Amount of Unrealized Gain (Loss) Recognized
			Year Ended					Year Ended						Year Ended
			December 31, 2014					December 31, 2013						December 31, 2012
			Derivative			Hedged Item		Derivative			Hedged Item			Derivative			Hedged Item
			(In thousands)
	Derivatives in fair value hedging relationships
	Interest rate swap agreements:
	Fixed rate long-term borrowings(a)		$	(29,624	)	$	28,870	$	(40,304	)	$	38,986		$	(4,123	)	$	3,724
	Derivatives not designated as hedging instruments
	Trading:
	Interest rate contracts(b)		$	3,398				$	9,824					$	8,004
	Foreign exchange and other option and futures contracts(b)			(6,719	)				(3,369	)					(3,970	)
	Total		$	(3,321	)			$	6,455					$	4,034
	(a)	Reported as other revenues from operations.
	(b)	Reported as trading account and foreign exchange gains.

Fair_value_measurements_Tables

Fair value measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis	The following tables present assets and liabilities at December 31, 2014 and 2013 measured at estimated fair value on a recurring basis:
			Fair Value			Level 1(a)			Level 2(a)			Level 3
			Measurements at
			December 31,
			2014
			(In thousands)
	Trading account assets		$	308,175			51,416			256,759			—
	Investment securities available for sale:
	U.S. Treasury and federal agencies			161,947			—			161,947			—
	Obligations of states and political subdivisions			8,198			—			8,198			—
	Mortgage-backed securities:
	Government issued or guaranteed			8,731,123			—			8,731,123			—
	Privately issued			103			—			—			103
	Collateralized debt obligations			50,316			—			—			50,316
	Other debt securities			121,488			—			121,488			—
	Equity securities			83,757			64,841			18,916			—
				9,156,932			64,841			9,041,672			50,419
	Real estate loans held for sale			742,249			—			742,249			—
	Other assets(b)			92,129			—			74,733			17,396
	Total assets		$	10,299,485			116,257			10,115,413			67,815
	Trading account liabilities		$	203,464			—			203,464			—
	Other liabilities(b)			8,596			—			8,547			49
	Total liabilities		$	212,060			—			212,011			49
			Fair Value			Level 1(a)			Level 2(a)			Level 3
			Measurements  at
			December 31,
			2013
			(In thousands)
	Trading account assets		$	376,131			51,386			324,745			—
	Investment securities available for sale:
	U.S. Treasury and federal agencies			37,776			—			37,776			—
	Obligations of states and political subdivisions			10,811			—			10,811			—
	Mortgage-backed securities:
	Government issued or guaranteed			4,165,086			—			4,165,086			—
	Privately issued			1,850			—			—			1,850
	Collateralized debt obligations			63,083			—			—			63,083
	Other debt securities			120,085			—			120,085			—
	Equity securities			133,095			82,450			50,645			—
				4,531,786			82,450			4,384,403			64,933
	Real estate loans held for sale			468,650			—			468,650			—
	Other assets(b)			123,568			—			115,952			7,616
	Total assets		$	5,500,135			133,836			5,293,750			72,549
	Trading account liabilities		$	249,797			—			249,797			—
	Other liabilities(b)			4,392			—			717			3,675
	Total liabilities		$	254,189			—			250,514			3,675
	(a)	There were no significant transfers between Level 1 and Level 2 of the fair value hierarchy during the years ended December 31, 2014 and 2013.
	(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 year ended December 31, 2014 were as follows:
			Investment Securities Available for Sale						Other
									Assets  and
									Other
			Privately Issued			Collateralized			Liabilities
			Mortgage-			Debt
			backed			Obligations
			Securities
			(In thousands)
	Balance — January 1, 2014		$	1,850		$	63,083		$	3,941
	Total gains realized/unrealized:
	Included in earnings			—			—			83,417	(b)
	Included in other comprehensive income			271	(e)		8,209	(e)		—
	Settlements			(2,018	)		(20,976	)		—
	Transfers in and/or out of Level 3(c)			—			—			(70,011	)(d)
	Balance — December 31, 2014		$	103		$	50,316		$	17,347
	Changes in unrealized gains included in earnings related to assets still held at December 31, 2014		$	—		$	—		$	18,196	(b)
	The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the year ended December 31, 2013 were as follows:
			Investment Securities Available for Sale						Other
									Assets  and
									Other
			Privately			Collateralized			Liabilities
			Issued			Debt
			Mortgage-			Obligations
			backed
			Securities
			(In thousands)
	Balance — January 1, 2013		$	1,023,886		$	61,869		$	47,859
	Total gains (losses) realized/unrealized:
	Included in earnings			(56,102	)(a)		—			97,845	(b)
	Included in other comprehensive income			116,359	(e)		4,508	(e)		—
	Sales			(978,608	)		—			—
	Settlements			(103,685	)		(3,294	)		—
	Transfers in and/or out of Level 3(c)			—			—			(141,763	)(d)
	Balance — December 31, 2013		$	1,850		$	63,083		$	3,941
	Changes in unrealized gains included in earnings related to assets still held at December 31, 2013		$	—		$	—		$	3,431	(b)
	The changes in Level 3 assets and liabilities measured at estimated fair value on a recurring basis during the year ended December 31, 2012 were as follows:
			Investment Securities Available for Sale						Other Assets
									and Other
			Privately			Collateralized			Liabilities
			Issued			Debt
			Mortgage-			Obligations
			backed
			Securities
			(In thousands)
	Balance — January 1, 2012		$	1,151,285		$	52,500		$	6,923
	Total gains (losses) realized/unrealized:
	Included in earnings			(42,467	)(a)		—			212,281	(b)
	Included in other comprehensive income			114,592	(e)		12,214	(e)		—
	Settlements			(199,524	)		(2,845	)		—
	Transfers in and/or out of Level 3(c)			—			—			(171,345	)(d)
	Balance — December 31, 2012		$	1,023,886		$	61,869		$	47,859
	Changes in unrealized gains (losses) included in earnings related to assets still held at December 31, 2012		$	(42,467	)(a)	$	—		$	47,859	(b)
	(a)	Reported as an OTTI impairment loss or as gain (loss) on bank investment securities in the consolidated statement of income.
	(b)	Reported as mortgage banking revenues in the consolidated statement of income and includes the fair value of commitment issuances and expirations.
	(c)	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.
	(d)	Transfers out of Level 3 consist of interest rate locks transferred to closed loans.
	(e)	Reported as net unrealized gains on investment securities in the consolidated statement of comprehensive income.
Quantitative Information Related to Significant Unobservable Inputs	The following tables present quantitative information about significant unobservable inputs used in the fair value measurements for Level 3 assets and liabilities at December 31, 2014 and 2013:
			Fair Value at			Valuation		Unobservable	Range
			December  31,			Technique		Input/Assumptions	(Weighted-
			2014						Average)
			(In thousands)
	Recurring fair value measurements:
	Privately issued mortgage–backed securities		$	103		Two independent pricing quotes		—	—
	Collateralized debt obligations			50,316		Discounted cash flow		Probability of default	12%-57% (36%)
								Loss severity	100%
	Net other assets (liabilities)(a)			17,347		Discounted cash flow		Commitment expirations	0%-96% (17%)
	(a)	Other Level 3 assets (liabilities) consist of commitments to originate real estate loans.
			Fair Value at			Valuation		Unobservable	Range
			December 31,			Technique		Input/Assumptions	(Weighted-
			2013						Average)
			(In thousands)
	Recurring fair value measurements:
	Privately issued mortgage–backed securities		$	1,850		Two independent pricing quotes		—	—
	Collateralized debt obligations			63,083		Discounted cash flow		Probability of default	17%-55% (39%)
								Loss severity	100%
	Net other assets (liabilities)(a)			3,941		Discounted cash flow		Commitment	0%-90% (20%)
								expirations
	(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:
			December 31, 2014
			Carrying			Estimated			Level 1			Level 2			Level 3
			Amount			Fair  Value
			(In thousands)
	Financial assets:
	Cash and cash equivalents		$	1,373,357		$	1,373,357		$	1,296,923		$	76,434		$	—
	Interest-bearing deposits at banks			6,470,867			6,470,867			—			6,470,867			—
	Trading account assets			308,175			308,175			51,416			256,759			—
	Investment securities			12,993,542			13,023,956			64,841			12,750,396			208,719
	Loans and leases:
	Commercial loans and leases			19,461,292			19,188,574			—			—			19,188,574
	Commercial real estate loans			27,567,569			27,487,818			—			307,667			27,180,151
	Residential real estate loans			8,657,301			8,729,056			—			5,189,086			3,539,970
	Consumer loans			10,982,794			10,909,623			—			—			10,909,623
	Allowance for credit losses			(919,562	)		—			—			—			—
	Loans and leases, net			65,749,394			66,315,071			—			5,496,753			60,818,318
	Accrued interest receivable			227,348			227,348			—			227,348			—
	Financial liabilities:
	Noninterest-bearing deposits		$	(26,947,880	)	$	(26,947,880	)		—		$	(26,947,880	)		—
	Savings deposits and NOW accounts			(43,393,618	)		(43,393,618	)		—			(43,393,618	)		—
	Time deposits			(3,063,973	)		(3,086,126	)		—			(3,086,126	)		—
	Deposits at Cayman Islands office			(176,582	)		(176,582	)		—			(176,582	)		—
	Short-term borrowings			(192,676	)		(192,676	)		—			(192,676	)		—
	Long-term borrowings			(9,006,959	)		(9,139,789	)		—			(9,139,789	)		—
	Accrued interest payable			(63,372	)		(63,372	)		—			(63,372	)		—
	Trading account liabilities			(203,464	)		(203,464	)		—			(203,464	)		—
	Other financial instruments:
	Commitments to originate real estate loans for sale		$	17,347		$	17,347			—		$	—		$	17,347
	Commitments to sell real estate loans			(7,065	)		(7,065	)		—			(7,065	)		—
	Other credit-related commitments			(119,079	)		(119,079	)		—			—			(119,079	)
	Interest rate swap agreements used for interest rate risk management			73,251			73,251			—			73,251			—
			December 31, 2013
			Carrying			Estimated			Level 1			Level 2			Level 3
			Amount			Fair  Value
			(In thousands)
	Financial assets:
	Cash and cash equivalents		$	1,672,934		$	1,672,934		$	1,596,877		$	76,057		$	—
	Interest-bearing deposits at banks			1,651,138			1,651,138			—			1,651,138			—
	Trading account assets			376,131			376,131			51,386			324,745			—
	Investment securities			8,796,497			8,690,494			82,450			8,384,106			223,938
	Loans and leases:
	Commercial loans and leases			18,705,216			18,457,288			—			—			18,457,288
	Commercial real estate loans			26,148,208			26,018,195			—			67,505			25,950,690
	Residential real estate loans			8,928,221			8,867,872			—			5,432,207			3,435,665
	Consumer loans			10,291,514			10,201,087			—			—			10,201,087
	Allowance for credit losses			(916,676	)		—			—			—			—
	Loans and leases, net			63,156,483			63,544,442			—			5,499,712			58,044,730
	Accrued interest receivable			222,558			222,558			—			222,558			—
	Financial liabilities:
	Noninterest-bearing deposits		$	(24,661,007	)	$	(24,661,007	)		—		$	(24,661,007	)		—
	Savings deposits and NOW accounts			(38,611,021	)		(38,611,021	)		—			(38,611,021	)		—
	Time deposits			(3,523,838	)		(3,542,789	)		—			(3,542,789	)		—
	Deposits at Cayman Islands office			(322,746	)		(322,746	)		—			(322,746	)		—
	Short-term borrowings			(260,455	)		(260,455	)		—			(260,455	)		—
	Long-term borrowings			(5,108,870	)		(5,244,902	)		—			(5,244,902	)		—
	Accrued interest payable			(43,419	)		(43,419	)		—			(43,419	)		—
	Trading account liabilities			(249,797	)		(249,797	)		—			(249,797	)		—
	Other financial instruments:
	Commitments to originate real estate loans for sale		$	3,941		$	3,941			—		$	—		$	3,941
	Commitments to sell real estate loans			12,360			12,360			—			12,360			—
	Other credit-related commitments			(118,886	)		(118,886	)		—			—			(118,886	)
	Interest rate swap agreements used for interest rate risk management			102,875			102,875			—			102,875			—

Commitments_and_contingencies_

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
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.
		December 31
		2014		2013
		(In thousands)
	Commitments to extend credit
	Home equity lines of credit	$	6,194,516	$	6,218,823
	Commercial real estate loans to be sold		212,257		62,386
	Other commercial real estate and construction		4,834,699		3,919,545
	Residential real estate loans to be sold		432,352		469,869
	Other residential real estate		524,399		384,617
	Commercial and other		11,080,856		10,419,545
	Standby letters of credit		3,706,888		3,600,528
	Commercial letters of credit		46,965		53,284
	Financial guarantees and indemnification contracts		2,490,050		2,457,633
	Commitments to sell real estate loans		1,237,294		854,656
Minimum Lease Payments Under Noncancelable Operating Leases	Minimum lease payments under noncancelable operating leases are summarized in the following table:
		(In thousands)
	Year ending December 31:
	2015	$	87,063
	2016		83,315
	2017		70,108
	2018		56,024
	2019		45,079
	Later years		113,390
		$	454,979

Segment_information_Tables

Segment information (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Information about Company's Segments	Information about the Company’s segments is presented in the accompanying table. Income statement amounts are in thousands of dollars. Balance sheet amounts are in millions of dollars.
									For the Years Ended December 31, 2014, 2013 and 2012
			Business Banking									Commercial Banking						Commercial Real Estate									Discretionary Portfolio
			2014			2013			2012			2014		2013		2012		2014			2013			2012			2014		2013			2012
	Net interest income(a)		$	317,356		$	325,521		$	347,067		$	745,218	$	758,231	$	753,678	$	539,600		$	570,786		$	531,398		$	74,204	$	66,157		$	66,303
	Noninterest income			105,370			102,945			103,283			259,832		263,766		253,808		127,445			130,895			133,120			27,464		(2,126	)		(76,113	)
				422,726			428,466			450,350			1,005,050		1,021,997		1,007,486		667,045			701,681			664,518			101,668		64,031			(9,810	)
	Provision for credit losses			18,885			26,450			22,245			33,197		76,818		15,781		(6,476	)		7,365			4,238			16,547		16,670			44,305
	Amortization of core deposit and other intangible assets			—			—			—			—		—		—		—			—			—			—		—			—
	Depreciation and other amortization			405			198			122			588		564		567		16,278			14,296			11,004			891		1,330			2,065
	Other noninterest expense			200,802			214,043			179,428			274,697		288,842		262,820		207,757			214,246			190,879			33,934		30,431			31,006
	Income (loss) before taxes			202,634			187,775			248,555			696,568		655,773		728,318		449,486			465,774			458,397			50,296		15,600			(87,186	)
	Income tax expense (benefit)			82,825			76,735			101,484			285,429		264,433		296,894		133,357			143,981			149,321			2,198		(14,368	)		(54,071	)
	Net income (loss)		$	119,809		$	111,040		$	147,071		$	411,139	$	391,340	$	431,424	$	316,129		$	321,793		$	309,076		$	48,098	$	29,968		$	(33,115	)
	Average total assets (in millions)		$	5,281		$	5,080		$	4,909		$	22,892	$	21,655	$	19,946	$	17,113		$	17,150		$	16,437		$	20,798	$	16,480		$	16,583
	Capital expenditures (in millions)		$	2		$	1		$	—		$	—	$	—	$	—	$	—		$	—		$	—		$	—	$	—		$	—
									For the Years Ended December 31, 2014, 2013 and 2012
			Residential Mortgage									Retail Banking						All Other									Total
			Banking
			2014			2013			2012			2014		2013		2012		2014			2013			2012			2014		2013			2012
	Net interest income(a)		$	90,123		$	98,496		$	78,058		$	741,109	$	810,134	$	902,906	$	168,836		$	43,904		$	(80,894	)	$	2,676,446	$	2,673,229		$	2,598,516
	Noninterest income			331,391			325,474			402,211			335,501		373,362		349,571		592,270			670,889			501,390			1,779,273		1,865,205			1,667,270
				421,514			423,970			480,269			1,076,610		1,183,496		1,252,477		761,106			714,793			420,496			4,455,719		4,538,434			4,265,786
	Provision for credit losses			(2,357	)		(11,711	)		17,169			77,158		72,502		95,345		(12,954	)		(3,094	)		4,917			124,000		185,000			204,000
	Amortization of core deposit and other intangible assets			—			—			—			—		—		—		33,824			46,912			60,631			33,824		46,912			60,631
	Depreciation and other amortization			47,108			48,716			46,902			37,788		34,599		32,734		61,848			57,120			50,536			164,906		156,823			143,930
	Other noninterest expense			222,396			225,794			195,604			759,569		768,644		751,916		844,972			690,150			693,046			2,544,127		2,432,150			2,304,699
	Income (loss) before taxes			154,367			161,171			220,594			202,095		307,751		372,482		(166,584	)		(76,295	)		(388,634	)		1,588,862		1,717,549			1,552,526
	Income tax expense (benefit)			59,361			61,779			85,671			82,179		125,350		151,616		(122,733	)		(78,841	)		(207,887	)		522,616		579,069			523,028
	Net income (loss)		$	95,006		$	99,392		$	134,923		$	119,916	$	182,401	$	220,866	$	(43,851	)	$	2,546		$	(180,747	)	$	1,066,246	$	1,138,480		$	1,029,498
	Average total assets (in millions)		$	3,333		$	2,858		$	2,451		$	10,449	$	10,997	$	11,705	$	12,277		$	9,442		$	7,952		$	92,143	$	83,662		$	79,983
	Capital expenditures (in millions)		$	—		$	—		$	1		$	14	$	40	$	15	$	57		$	89		$	76		$	73	$	130		$	92
	(a)	Net interest income is the difference between actual taxable-equivalent interest earned on assets and interest paid on liabilities by a segment and a funding charge (credit) based on the Company’s internal funds transfer pricing 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 $23,642,000 in 2014, $24,971,000 in 2013 and $26,391,000 in 2012 and is eliminated in “All Other” net interest income and income tax expense (benefit).
Intersegment Activity Eliminated in Arriving at Consolidated Totals was Included in "All Other" Category	The amount of intersegment activity eliminated in arriving at consolidated totals was included in the “All Other” category as follows:
			Year Ended December 31
			2014			2013			2012
			(In thousands)
	Revenues		$	(49,800	)	$	(50,128	)	$	(71,452	)
	Expenses			(12,014	)		(16,235	)		(17,313	)
	Income taxes (benefit)			(15,375	)		(13,791	)		(22,029	)
	Net income (loss)			(22,411	)		(20,102	)		(32,110	)

Regulatory_matters_Tables

Regulatory matters (Tables)	12 Months Ended
	Dec. 31, 2014
Banking and Thrift [Abstract]
Capital Ratios and Amounts of Company and its Banking Subsidiaries	The capital ratios and amounts of the Company and its banking subsidiaries as of December 31, 2014 and 2013 are presented below:
			M&T			M&T Bank			Wilmington
			(Consolidated)						Trust,  N.A.
			(Dollars in thousands)
	December 31, 2014:
	Tier 1 capital
	Amount		$	9,644,765		$	8,043,185		$	435,558
	Ratio(a)			12.47	%		10.46	%		57.22	%
	Minimum required amount(b)			3,093,874			3,077,101			30,447
	Total capital
	Amount			11,767,308			10,048,277			439,867
	Ratio(a)			15.21	%		13.06	%		57.79	%
	Minimum required amount(b)			6,187,747			6,154,201			60,893
	Leverage
	Amount			9,644,765			8,043,185			435,558
	Ratio(c)			10.17	%		8.56	%		9.98	%
	Minimum required amount(b)			3,793,836			3,760,364			174,613
	December 31, 2013:
	Tier 1 capital
	Amount		$	8,792,035		$	7,341,506		$	420,330
	Ratio(a)			12	%		10.08	%		73.79	%
	Minimum required amount(b)			2,930,925			2,914,246			22,786
	Total capital
	Amount			11,045,589			9,445,770			424,975
	Ratio(a)			15.07	%		12.96	%		74.6	%
	Minimum required amount(b)			5,861,849			5,828,491			45,573
	Leverage
	Amount			8,792,035			7,341,506			420,330
	Ratio(c)			10.78	%		9.09	%		19.8	%
	Minimum required amount(b)			2,446,476			2,422,096			63,678
	(a)	The ratio of capital to risk-weighted assets, as defined by regulation.
	(b)	Minimum amount of capital to be considered adequately capitalized, as defined by regulation.
	(c)	The ratio of capital to average assets, as defined by regulation.

Parent_company_financial_state1

Parent company financial statements (Tables)	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheet	Condensed Balance Sheet
		December 31
		2014			2013
		(In thousands)
	Assets
	Cash in subsidiary bank	$	11,306		$	10,729
	Due from consolidated bank subsidiaries
	Money-market savings		1,096,533			968,274
	Current income tax receivable		—			1,914
	Other		12			1,894
	Total due from consolidated bank subsidiaries		1,096,545			972,082
	Investments in consolidated subsidiaries
	Banks and bank holding company		11,945,516			11,364,657
	Other		16,217			16,212
	Investments in unconsolidated subsidiaries (note 19)		33,578			33,751
	Investment in Bayview Lending Group LLC		46,716			73,883
	Other assets		81,034			80,098
	Total assets	$	13,230,912		$	12,551,412
	Liabilities
	Accrued expenses and other liabilities	$	59,950		$	62,817
	Long-term borrowings		835,066			1,183,063
	Total liabilities		895,016			1,245,880
	Shareholders’ equity		12,335,896			11,305,532
	Total liabilities and shareholders’ equity	$	13,230,912		$	12,551,412
Condensed Statement of Income	Condensed Statement of Income
		Year Ended December 31
		2014			2013			2012
		(In thousands, except per share)
	Income
	Dividends from consolidated bank subsidiaries	$	480,000		$	700,000		$	700,000
	Equity in earnings of Bayview Lending Group LLC		(16,672	)		(16,126	)		(21,511	)
	Other income		7,755			9,992			8,755
	Total income		471,083			693,866			687,244
	Expense
	Interest on long-term borrowings		47,700			73,115			82,286
	Other expense		15,107			15,994			19,226
	Total expense		62,807			89,109			101,512
	Income before income taxes and equity in undistributed income of subsidiaries		408,276			604,757			585,732
	Income tax credits		27,284			35,986			43,149
	Income before equity in undistributed income of subsidiaries		435,560			640,743			628,881
	Equity in undistributed income of subsidiaries
	Net income of subsidiaries		1,110,686			1,197,737			1,100,617
	Less: dividends received		(480,000	)		(700,000	)		(700,000	)
	Equity in undistributed income of subsidiaries		630,686			497,737			400,617
	Net income	$	1,066,246		$	1,138,480		$	1,029,498
	Net income per common share
	Basic	$	7.47		$	8.26		$	7.57
	Diluted		7.42			8.2			7.54
Condensed Statement of Cash Flow	Condensed Statement of Cash Flows
		Year Ended December 31
		2014			2013			2012
		(In thousands)
	Cash flows from operating activities
	Net income	$	1,066,246		$	1,138,480		$	1,029,498
	Adjustments to reconcile net income to net cash provided by operating activities
	Equity in undistributed income of subsidiaries		(630,686	)		(497,737	)		(400,617	)
	Provision for deferred income taxes		(6,522	)		1,535			1,724
	Net change in accrued income and expense		23,419			31,979			6,798
	Net cash provided by operating activities		452,457			674,257			637,403
	Cash flows from investing activities
	Proceeds from sales of investment securities		—			—			411
	Investment in subsidiary		—			(140,000	)		—
	Other, net		10,721			3,295			324
	Net cash provided (used) by investing activities		10,721			(136,705	)		735
	Cash flows from financing activities
	Payments on long-term borrowings		(350,010	)		—			(300,000	)
	Dividends paid — common		(371,199	)		(365,349	)		(357,717	)
	Dividends paid — preferred		(70,234	)		(53,450	)		(53,450	)
	Proceeds from issuance of preferred stock		346,500			—			—
	Other, net		110,601			140,799			143,352
	Net cash used by financing activities		(334,342	)		(278,000	)		(567,815	)
	Net increase in cash and cash equivalents		128,836			259,552			70,323
	Cash and cash equivalents at beginning of year		979,003			719,451			649,128
	Cash and cash equivalents at end of year	$	1,107,839		$	979,003		$	719,451
	Supplemental disclosure of cash flow information
	Interest received during the year	$	2,094		$	2,224		$	1,970
	Interest paid during the year		47,003			71,090			80,090
	Income taxes received during the year		24,588			45,237			21,878

Recovered_Sheet1

Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Delinquent period of loans resulting in accrued interest being charged against income	90 days
Delinquent period of loans secured by real estate resulting in charge off	150 days
Estimated useful lives	8 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Loans secured by real estate delinquent period threshold for return to accrual status	90 days
Consumer loan delinquent period threshold for consideration for charge off	180 days
Estimated useful lives	10 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Consumer loan delinquent period threshold for consideration for charge off	91 days
Estimated useful lives	5 years
Income tax benefit recognition criteria percentage threshold	50.00%

Acquisitions_Additional_Inform

Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 27, 2012
Business Acquisition [Line Items]
Purchase consideration per common share				$0.08
Total consideration to be paid	$5,400,000,000
Assets	96,685,535,000	85,162,391,000
Loans	65,749,394,000	63,156,483,000
Investment securities	12,993,542,000	8,796,497,000
Liabilities	84,349,639,000	73,856,859,000
Deposits	73,582,053,000	67,118,612,000
Common Stock [Member]
Business Acquisition [Line Items]
Percentage of total consideration				60.00%
Cash [Member]
Business Acquisition [Line Items]
Percentage of total consideration				40.00%
Hudson City [Member]
Business Acquisition [Line Items]
Assets	36,600,000,000
Loans	21,700,000,000
Investment securities	7,900,000,000
Liabilities	31,800,000,000
Deposits	19,400,000,000
Merger-related expenses	$0	$12,364,000	$9,879,000

Acquisitions_Summary_of_Merger

Acquisitions - Summary of Merger-Related Expenses (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of merger-related expenses
Salaries and employee benefits	$1,404,950,000	$1,355,178,000	$1,314,540,000
Equipment and net occupancy	269,299,000	264,327,000	257,551,000
Printing, postage and supplies	38,201,000	39,557,000	41,929,000
Other costs of operations	941,052,000	860,327,000	733,499,000
Hudson City [Member]
Summary of merger-related expenses
Salaries and employee benefits		836,000	4,997,000
Equipment and net occupancy		690,000	15,000
Printing, postage and supplies		1,825,000
Other costs of operations		9,013,000	4,867,000
Total merger-related expenses	$0	$12,364,000	$9,879,000

Investment_Securities_Amortize

Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Other securities, Amortized cost	$328,742	$298,581
Other securities, Estimated fair value	328,742	298,581
Investment securities, available for sale, amortized cost	8,919,324	4,444,365
Investment securities available for sale, gross unrealized gains	258,851	127,333
Investment securities available for sale, gross unrealized losses	21,243	39,912
Investment securities available for sale, estimated fair value	9,156,932	4,531,786
Amortized cost for held to maturity	3,507,868	3,966,130
Gross unrealized gains for held to maturity	82,179	19,904
Gross unrealized losses for held to maturity	51,765	125,907
Estimated fair value for held to maturity	3,538,282	3,860,127
Total Amortized cost	12,755,934	8,709,076
Total for Gross unrealized gains	341,030	147,237
Total for Gross unrealized losses	73,008	165,819
Total for Estimated fair value	13,023,956	8,690,494
Government Issued or Guaranteed [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	8,507,571	4,123,435
Investment securities available for sale, gross unrealized gains	223,889	61,001
Investment securities available for sale, gross unrealized losses	337	19,350
Investment securities available for sale, estimated fair value	8,731,123	4,165,086
Amortized cost for held to maturity	3,149,320	3,567,905
Gross unrealized gains for held to maturity	78,485	16,160
Gross unrealized losses for held to maturity	7,000	65,149
Estimated fair value for held to maturity	3,220,805	3,518,916
Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	104	1,468
Investment securities available for sale, gross unrealized gains	2	387
Investment securities available for sale, gross unrealized losses	3	5
Investment securities available for sale, estimated fair value	103	1,850
Amortized cost for held to maturity	201,733	219,628
Gross unrealized gains for held to maturity	1,143
Gross unrealized losses for held to maturity	44,576	60,623
Estimated fair value for held to maturity	158,300	159,005
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	30,073	42,274
Investment securities available for sale, gross unrealized gains	21,276	21,666
Investment securities available for sale, gross unrealized losses	1,033	857
Investment securities available for sale, estimated fair value	50,316	63,083
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	8,027	10,484
Investment securities available for sale, gross unrealized gains	224	333
Investment securities available for sale, gross unrealized losses	53	6
Investment securities available for sale, estimated fair value	8,198	10,811
Amortized cost for held to maturity	148,961	169,684
Gross unrealized gains for held to maturity	2,551	3,744
Gross unrealized losses for held to maturity	189	135
Estimated fair value for held to maturity	151,323	173,293
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	138,240	137,828
Investment securities available for sale, gross unrealized gains	1,896	1,722
Investment securities available for sale, gross unrealized losses	18,648	19,465
Investment securities available for sale, estimated fair value	121,488	120,085
Amortized cost for held to maturity	7,854	8,913
Estimated fair value for held to maturity	7,854	8,913
U.S. Treasury and Federal Agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	161,408	37,396
Investment securities available for sale, gross unrealized gains	544	382
Investment securities available for sale, gross unrealized losses	5	2
Investment securities available for sale, estimated fair value	161,947	37,776
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	73,901	91,480
Investment securities available for sale, gross unrealized gains	11,020	41,842
Investment securities available for sale, gross unrealized losses	1,164	227
Investment securities available for sale, estimated fair value	$83,757	$133,095

Investment_Securities_Investme

Investment Securities - Investment Ratings of All Privately Issued Mortgage-Backed Securities, Collateralized Debt Obligations and Other Debt Securities (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	$534,992
Total securities with disclosed rating, Estimated Fair Value	497,582
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	156,988
Total securities with disclosed rating, Estimated Fair Value	159,521
Mortgage-backed Securities, Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	201,837
Total securities with disclosed rating, Estimated Fair Value	158,403
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	30,073
Total securities with disclosed rating, Estimated Fair Value	50,316
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Amortized Cost	146,094
Total securities with disclosed rating, Estimated Fair Value	129,342
A or Better [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	204,955
A or Better [Member] | Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	137,606
A or Better [Member] | Mortgage-backed Securities, Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	48,368
A or Better [Member] | Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	6,629
A or Better [Member] | Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	12,352
BBB [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	63,988
BBB [Member] | Mortgage-backed Securities, Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	19
BBB [Member] | Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	5,488
BBB [Member] | Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	58,481
BB [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	30,301
BB [Member] | Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	1,273
BB [Member] | Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	29,028
B or Less [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	167,275
B or Less [Member] | Mortgage-backed Securities, Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	109,949
B or Less [Member] | Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	36,926
B or Less [Member] | Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	20,400
Not Rated [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	31,063
Not Rated [Member] | Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	21,915
Not Rated [Member] | Mortgage-backed Securities, Privately Issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	67
Not Rated [Member] | Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Total securities with disclosed rating, Estimated Fair Value	$9,081

Investment_Securities_Amortize1

Investment Securities - Amortized Cost and Estimated Fair Value of Collateralized Mortgage Obligations (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Amortized Cost and Fair Value Debt Securities [Abstract]
Collateralized mortgage obligations, Amortized cost	$209,107	$231,040
Collateralized mortgage obligations, Estimated fair value	$165,860	$171,100

Investment_Securities_Addition

Investment Securities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
			Investment
Investment Holdings [Line Items]
Gross realized gains on sale of investment securities	$116,490,000
Gross realized losses on investment securities	60,033,000
Number of investment securities with aggregate gross unrealized losses			296
Unrealized losses on individual investment securities	165,819,000		73,008,000
Cost method investment securities			329,000,000
Investment securities pledged to secure debt carrying value			3,825,003,000
Pledged securities that can be sold or repledged	1,696,438,000		1,631,267,000
Available-for-Sale Securities [Member]
Investment Holdings [Line Items]
Investment securities pledged to secure debt carrying value			2,905,457,000
Privately Issued Mortgage-Backed Securities [Member]
Investment Holdings [Line Items]
Privately issued mortgage backed securities sold	1,000,000,000
Net loss on securities sold	46,302,000
Pre-tax other-than-temporary impairment losses	10,000,000	48,000,000
Visa Class B [Member]
Investment Holdings [Line Items]
Gain on sale of holdings	89,545,000
MasterCard Class B [Member]
Investment Holdings [Line Items]
Gain on sale of holdings	$13,208,000

Investment_Securities_Amortize2

Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt securities available for sale:
Due in one year or less	$7,412
Due after one year through five years	164,412
Due after five years through ten years	3,524
Due after ten years	162,400
Total available for sale (amortized cost)	337,748
Mortgage-backed securities available for sale	8,507,675
Total	8,845,423
Debt securities held to maturity:
Due in one year or less	23,107
Due after one year through five years	84,112
Due after five years through ten years	41,742
Due after ten years	7,854
Total available for held to maturity (amortized cost)	156,815
Mortgage-backed securities held to maturity	3,351,053
Amortized cost for held to maturity	3,507,868	3,966,130
Debt securities available for sale:
Due in one year or less	7,468
Due after one year through five years	165,340
Due after five years through ten years	3,577
Due after ten years	165,564
Total available for sale (fair value)	341,949
Mortgage-backed securities available for sale	8,731,226
Total	9,073,175
Debt securities held to maturity:
Due in one year or less	23,254
Due after one year through five years	85,457
Due after five years through ten years	42,612
Due after ten years	7,854
Total available for held to maturity (fair value)	159,177
Mortgage-backed securities held to maturity	3,379,105
Total	$3,538,282	$3,860,127

Investment_Securities_Investme1

Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	$65,554	$1,699,426
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	-2,659	-19,458
Estimated fair value, 12 months or more	103,914	116,330
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	-18,584	-20,454
Held to maturity, Estimated fair value, Less than 12 months	167,299	2,643,467
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	-545	-65,269
Held to maturity, Estimated fair value, 12 months or more	574,560	160,563
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	-51,220	-60,638
Total investment securities, fair value less than 12 months	232,853	4,342,893
Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses	-3,204	-84,727
Total of investment securities, fair value, 12 Months or More	678,474	276,893
Investment Securities Continuous Unrealized Loss Position Twelve Months or Longer Aggregate Losses	-69,804	-81,092
Government Issued or Guaranteed [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	39,001	1,697,094
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	-186	-19,225
Estimated fair value, 12 months or more	5,555	5,815
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	-151	-125
Held to maturity, Estimated fair value, Less than 12 months	137,413	2,629,950
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	-361	-65,149
Held to maturity, Estimated fair value, 12 months or more	446,780
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	-6,639
Privately Issued Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Held to maturity, Estimated fair value, 12 months or more	127,512	159,005
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	-44,576	-60,623
Privately Issued Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, 12 months or more	65	98
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	-3	-5
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	1,785
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	-52
Estimated fair value, 12 months or more	121	558
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	-1	-6
Held to maturity, Estimated fair value, Less than 12 months	29,886	13,517
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	-184	-120
Held to maturity, Estimated fair value, 12 months or more	268	1,558
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	-5	-15
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	6,505	745
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	-5	-2
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	2,108
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	-696
Estimated fair value, 12 months or more	5,512	6,257
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	-337	-857
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	14,017	1,428
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	-556	-4
Estimated fair value, 12 months or more	92,661	103,602
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	-18,092	-19,461
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	2,138	159
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	($1,164)	($227)

Loans_and_Leases_Total_Loans_a

Loans and Leases - Total Loans and Leases Outstanding (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Loans
Commercial, financial, etc.	$18,280,049	$17,477,238
Real estate:
Residential	8,636,794	8,911,554
Commercial	22,614,174	21,799,886
Construction	5,061,269	4,457,650
Consumer	10,969,879	10,280,527
Total loans	65,562,165	62,926,855
Leases
Commercial	1,337,204	1,398,928
Total loans and leases	66,899,369	64,325,783
Less: unearned discount	-230,413	-252,624
Total loans and leases, net of unearned discount	$66,668,956	$64,073,159

Loans_and_Leases_Additional_In

Loans and Leases - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loans And Leases Receivable [Line Items]
Residential mortgage loans securitized with Ginnie Mae		$1,300,000,000
Automobile loans securitized and sold	0	1,400,000,000
Recognized gain		42,382,000
Recognized gain sale of securities		20,683,000
Charges incurred for reimbursement of loan	4,000,000	17,000,000	28,000,000
Contractual principal and interest payments	198,000,000	331,000,000
Purchased impaired loans as a percentage of total assets	Less than 1% of the Company's assets	Less than 1% of the Company's assets
Interest income that would have been recognized on nonaccrual and renegotiated loans if those loans were accruing interest at their originally contracted terms	58,314,000	62,010,000	69,054,000
Interest on nonaccrual and renegotiated loans included in interest income	28,492,000	31,987,000	30,484,000
Exclusion limit of loans from related party disclosure	Less than $120,000
Borrowing by directors and certain officers of M&T and its banking subsidiaries and their associates	49,799,000	135,512,000
New borrowings by directors, certain officers and their associates	12,327,000
Repayments and other reductions of borrowings by directors, certain officers and their associates	98,040,000
Guaranteed amount included in the estimated residual value of leased assets associated with direct financing leases	48,000,000	54,000,000
Residential Mortgage Loans [Member]
Loans And Leases Receivable [Line Items]
Mortgage loans held for sale	435,000,000	401,000,000
Commercial Loans and Leases [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	10,400,000,000
Commercial Real Estate [Member]
Loans And Leases Receivable [Line Items]
Commercial real estate loans held for sale	308,000,000	68,000,000
Loans serviced for others sold with credit recourse	2,400,000,000
Loans pledged to secure outstanding borrowings from the FHLB of New York	9,700,000,000
Residential Mortgage Loans [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	5,300,000,000
Home Equity Loans and Lines of Credit [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	4,300,000,000
Other Consumer Loans [Member]
Loans And Leases Receivable [Line Items]
Loans pledged to secure outstanding borrowings from the FHLB of New York	$2,900,000,000

Loans_and_Leases_Outstanding_P

Loans and Leases - Outstanding Principal Balance and Carrying Amount of Loans that is Included in Consolidated Balance Sheet (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$3,070,268	$4,656,811
Carrying amount	2,596,545	4,007,452
Commercial, Financial, Leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	247,820	580,685
Real Estate Commercial [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	961,828	1,541,368
Residential Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	453,360	576,473
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$933,537	$1,308,926

Loans_and_Leases_Summary_of_Ch

Loans and Leases - Summary of Changes in Accretable Yield for Acquired Loans (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$37,230	$42,252	$30,805
Interest income	-21,263	-36,727	-40,551
Reclassifications from nonaccretable balance, net	60,551	31,705	51,998
Balance at end of period	76,518	37,230	42,252
Other [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	538,633	638,272	807,960
Interest income	-178,670	-247,295	-295,654
Reclassifications from nonaccretable balance, net	24,907	149,595	148,490
Other	12,509	-1,939	-22,524
Balance at end of period	$397,379	$538,633	$638,272

Loans_and_Leases_Summary_of_Cu

Loans and Leases - Summary of Current, Past Due and Nonaccrual Loans (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	$64,785,780	$61,664,881
30-89 Days past due	530,901	704,658
Purchased impaired	197,737	330,792
Nonaccrual	799,151	874,156
Loans and leases, net of unearned discount	66,668,956	64,073,159
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	19,228,265	18,489,474
30-89 Days past due	37,246	77,538
Purchased impaired	10,300	15,706
Nonaccrual	177,445	110,739
Loans and leases, net of unearned discount	19,461,292	18,705,216
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	22,208,491	21,236,071
30-89 Days past due	118,704	145,749
Purchased impaired	51,312	88,034
Nonaccrual	141,600	173,048
Loans and leases, net of unearned discount	22,556,939	21,741,858
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,273,607	1,025,984
30-89 Days past due	11,827	8,486
Purchased impaired	98,347	137,544
Nonaccrual	71,517	96,427
Loans and leases, net of unearned discount	1,465,140	1,276,512
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	3,484,932	2,986,598
30-89 Days past due	17,678	42,234
Purchased impaired	17,181	57,707
Nonaccrual	25,699	35,268
Loans and leases, net of unearned discount	3,545,490	3,129,838
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	7,640,368	7,630,368
30-89 Days past due	226,932	295,131
Purchased impaired	18,223	29,184
Nonaccrual	180,275	252,805
Loans and leases, net of unearned discount	8,318,013	8,545,837
Residential Alt-A [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	249,810	283,253
30-89 Days past due	11,774	18,009
Nonaccrual	77,704	81,122
Loans and leases, net of unearned discount	339,288	382,384
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	5,859,378	5,972,365
30-89 Days past due	42,945	40,537
Purchased impaired	2,374	2,617
Nonaccrual	89,291	78,516
Loans and leases, net of unearned discount	6,021,884	6,121,789
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	1,931,138	1,314,246
30-89 Days past due	30,500	29,144
Nonaccrual	17,578	21,144
Loans and leases, net of unearned discount	1,979,349	1,364,900
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	2,909,791	2,726,522
30-89 Days past due	33,295	47,830
Nonaccrual	18,042	25,087
Loans and leases, net of unearned discount	2,981,561	2,804,825
Non-Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	245,020	368,510
Non-Acquired [Member] | Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	1,805	4,981
Non-Acquired [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	22,170	63,353
Non-Acquired [Member] | Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	492	141
Non-Acquired [Member] | Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	216,489	294,649
Non-Acquired [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	4,064	5,386
Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	110,367	130,162
Acquired [Member] | Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	6,231	6,778
Acquired [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	14,662	35,603
Acquired [Member] | Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	9,350	7,930
Acquired [Member] | Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing		8,031
Acquired [Member] | Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	35,726	43,700
Acquired [Member] | Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	27,896	27,754
Acquired [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	133	366
Acquired [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or more past due and accruing	$16,369

Loans_and_Leases_Loan_Modifica

Loans and Leases - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	Modification	Modification	Modification
Financing Receivable, Modifications [Line Items]
Number of modifications	760	1,258	1,608
Pre-modification, Recorded Investment	$134,351	$258,075	$256,681
Post-modification, Recorded Investment	130,190	254,352	251,018
Financial Effects of Modification, Recorded Investment	-4,161	-3,723	-5,663
Financial Effects of Modification, Interest	-2,969	-4,691	-2,853
Principal Deferral [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	95	79	61
Pre-modification, Recorded Investment	29,035	16,389	23,888
Post-modification, Recorded Investment	23,628	16,002	22,456
Financial Effects of Modification, Recorded Investment	-5,407	-387	-1,432
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	39	27	24
Pre-modification, Recorded Investment	19,077	40,639	22,855
Post-modification, Recorded Investment	18,997	40,464	23,059
Financial Effects of Modification, Recorded Investment	-80	-175	204
Principal Deferral [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	2	18	23
Pre-modification, Recorded Investment	1,639	21,423	36,868
Post-modification, Recorded Investment	1,639	20,577	34,740
Financial Effects of Modification, Recorded Investment		-846	-2,128
Principal Deferral [Member] | Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	4	3	6
Pre-modification, Recorded Investment	6,703	590	81,062
Post-modification, Recorded Investment	6,611	521	79,312
Financial Effects of Modification, Recorded Investment	-92	-69	-1,750
Principal Deferral [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	28	32	36
Pre-modification, Recorded Investment	2,710	3,556	4,643
Post-modification, Recorded Investment	2,905	3,821	4,808
Financial Effects of Modification, Recorded Investment	195	265	165
Principal Deferral [Member] | Residential Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	6	10	7
Pre-modification, Recorded Investment	880	1,900	968
Post-modification, Recorded Investment	963	1,880	989
Financial Effects of Modification, Recorded Investment	83	-20	21
Principal Deferral [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	3	10	15
Pre-modification, Recorded Investment	280	859	1,285
Post-modification, Recorded Investment	280	861	1,285
Financial Effects of Modification, Recorded Investment		2
Principal Deferral [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	208	460	618
Pre-modification, Recorded Investment	3,293	6,148	8,347
Post-modification, Recorded Investment	3,293	6,148	8,347
Principal Deferral [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	33	36	80
Pre-modification, Recorded Investment	245	332	1,201
Post-modification, Recorded Investment	245	332	1,201
Interest Rate Reduction [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		1
Pre-modification, Recorded Investment		104
Post-modification, Recorded Investment		335
Financial Effects of Modification, Recorded Investment		231
Financial Effects of Modification, Interest		-54
Interest Rate Reduction [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1		2
Pre-modification, Recorded Investment	255		665
Post-modification, Recorded Investment	252		708
Financial Effects of Modification, Recorded Investment	-3		43
Financial Effects of Modification, Interest	-48		-129
Interest Rate Reduction [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	11		1
Pre-modification, Recorded Investment	1,146		109
Post-modification, Recorded Investment	1,222		109
Financial Effects of Modification, Recorded Investment	76
Financial Effects of Modification, Interest	-152		-20
Interest Rate Reduction [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	6	1	1
Pre-modification, Recorded Investment	535	99	144
Post-modification, Recorded Investment	535	99	144
Financial Effects of Modification, Interest	-120	-8	-6
Interest Rate Reduction [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	9	15	22
Pre-modification, Recorded Investment	152	235	328
Post-modification, Recorded Investment	152	235	328
Financial Effects of Modification, Interest	-12	-22	-24
Interest Rate Reduction [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	4	1	22
Pre-modification, Recorded Investment	293	12	515
Post-modification, Recorded Investment	293	12	515
Financial Effects of Modification, Interest	-63	-2	-85
Other [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	3	4	3
Pre-modification, Recorded Investment	29,912	50,433	2,967
Post-modification, Recorded Investment	31,604	50,924	3,052
Financial Effects of Modification, Recorded Investment	1,692	491	85
Other [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	2
Pre-modification, Recorded Investment	650	449
Post-modification, Recorded Investment		475
Financial Effects of Modification, Recorded Investment	-650	26
Other [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		1
Pre-modification, Recorded Investment		4,039
Post-modification, Recorded Investment		3,888
Financial Effects of Modification, Recorded Investment		-151
Other [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	1
Pre-modification, Recorded Investment	188	195
Post-modification, Recorded Investment	188	195
Other [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		1
Pre-modification, Recorded Investment		106
Post-modification, Recorded Investment		106
Other [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	42	78	67
Pre-modification, Recorded Investment	255	339	300
Post-modification, Recorded Investment	255	339	300
Other [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	2	13
Pre-modification, Recorded Investment	45	14	54
Post-modification, Recorded Investment	45	14	54
Combination of Concession Types [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	7	11	5
Pre-modification, Recorded Investment	19,167	6,229	628
Post-modification, Recorded Investment	19,030	5,578	740
Financial Effects of Modification, Recorded Investment	-137	-651	112
Financial Effects of Modification, Interest	-20	-458	-102
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	7	9	7
Pre-modification, Recorded Investment	1,152	2,649	1,637
Post-modification, Recorded Investment	1,198	3,040	1,656
Financial Effects of Modification, Recorded Investment	46	391	19
Financial Effects of Modification, Interest	-264	-250	-351
Combination of Concession Types [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		3	7
Pre-modification, Recorded Investment		15,580	37,602
Post-modification, Recorded Investment		15,514	36,148
Financial Effects of Modification, Recorded Investment		-66	-1,454
Financial Effects of Modification, Interest		-535
Combination of Concession Types [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	30	61	62
Pre-modification, Recorded Investment	4,211	73,940	12,886
Post-modification, Recorded Investment	4,287	70,854	13,146
Financial Effects of Modification, Recorded Investment	76	-3,086	260
Financial Effects of Modification, Interest	-483	-924	-657
Combination of Concession Types [Member] | Residential Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	21	19	38
Pre-modification, Recorded Investment	3,806	2,826	8,525
Post-modification, Recorded Investment	3,846	3,148	8,717
Financial Effects of Modification, Recorded Investment	40	322	192
Financial Effects of Modification, Interest	-386	-790	-159
Combination of Concession Types [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	47	28	29
Pre-modification, Recorded Investment	5,031	2,190	2,332
Post-modification, Recorded Investment	5,031	2,190	2,332
Financial Effects of Modification, Interest	-560	-270	-368
Combination of Concession Types [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	81	225	375
Pre-modification, Recorded Investment	1,189	2,552	5,857
Post-modification, Recorded Investment	1,189	2,552	5,857
Financial Effects of Modification, Interest	-100	-191	-684
Combination of Concession Types [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	70	120	84
Pre-modification, Recorded Investment	2,502	4,248	1,015
Post-modification, Recorded Investment	2,502	4,248	1,015
Financial Effects of Modification, Interest	($761)	($1,187)	($268)

Loans_and_Leases_Summary_of_Le

Loans and Leases - Summary of Lease Financing Receivables (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Direct financings:
Lease payments receivable	$1,022,133	$1,052,214
Estimated residual value of leased assets	79,525	85,595
Unearned income	-103,777	-114,101
Investment in direct financings	997,881	1,023,708
Leveraged leases:
Lease payments receivable	102,457	127,821
Estimated residual value of leased assets	133,089	133,298
Unearned income	-44,288	-47,188
Investment in leveraged leases	191,258	213,931
Total investment in leases.	1,189,139	1,237,639
Deferred taxes payable arising from leveraged leases	$169,101	$172,296

Loans_and_Leases_Minimum_Futur

Loans and Leases - Minimum Future Lease Payments to be Received from Lease Financings (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Receivables [Abstract]
2015	$268,086
2016	242,248
2017	177,539
2018	127,985
2019	92,205
Later years	216,527
Total	$1,124,590

Allowance_for_Credit_Losses_Ch

Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$916,676	$925,860	$908,290
Provision for credit losses	124,000	185,000	204,000
Allowance related to loans sold or securitized		-11,000
Net charge-offs
Charge-offs	-178,742	-253,510	-230,755
Recoveries	57,628	70,326	44,325
Net charge-offs	-121,114	-183,184	-186,430
Ending balance	919,562	916,676	925,860
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	273,383	246,759	234,022
Provision for credit losses	51,410	124,180	42,510
Net charge-offs
Charge-offs	-58,943	-109,329	-41,148
Recoveries	22,188	11,773	11,375
Net charge-offs	-36,755	-97,556	-29,773
Ending balance	288,038	273,383	246,759
Real Estate Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	324,978	337,101	367,637
Provision for credit losses	-13,779	275	5,211
Net charge-offs
Charge-offs	-14,058	-34,595	-41,945
Recoveries	10,786	22,197	6,198
Net charge-offs	-3,272	-12,398	-35,747
Ending balance	307,927	324,978	337,101
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,656	88,807	91,915
Provision for credit losses	-3,974	3,149	34,864
Net charge-offs
Charge-offs	-21,351	-23,621	-44,314
Recoveries	8,579	10,321	6,342
Net charge-offs	-12,772	-13,300	-37,972
Ending balance	61,910	78,656	88,807
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	164,644	179,418	143,121
Provision for credit losses	89,704	56,156	119,235
Allowance related to loans sold or securitized		-11,000
Net charge-offs
Charge-offs	-84,390	-85,965	-103,348
Recoveries	16,075	26,035	20,410
Net charge-offs	-68,315	-59,930	-82,938
Ending balance	186,033	164,644	179,418
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	75,015	73,775	71,595
Provision for credit losses	639	1,240	2,180
Net charge-offs
Ending balance	$75,654	$75,015	$73,775

Allowance_for_Credit_Losses_Ad

Allowance for Credit Losses - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan delinquent period	90 days
Delinquency period for loan level collectability analysis consumer mortgage	More than 150 days
Carrying value of loans for which partial charge-off has been recognized	$65,749,394,000	$63,156,483,000
Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value of loans for which partial charge-off has been recognized	63,000,000	58,000,000
Mortgage loans, customer balance outstanding	27,000,000	26,000,000
Home Equity Loans and Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value of loans for which partial charge-off has been recognized	18,000,000	18,000,000
Mortgage loans, customer balance outstanding	$28,000,000	$21,000,000

Allowance_for_Credit_Losses_Im

Allowance for Credit Losses - Impaired Loans and Leases (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule Of Financial Receivables [Line Items]
Recorded Investment	$762,455	$889,226
Unpaid Principal Balance	953,794	1,083,258
Related Allowance	82,643	92,608
Commercial, Financial, Leasing, etc. [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	206,318	118,386
Unpaid Principal Balance	246,639	145,187
Related Allowance	31,779	24,614
Commercial Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	150,732	178,841
Unpaid Principal Balance	175,152	216,658
Related Allowance	14,121	19,520
Residential Builder and Developer [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	76,452	105,677
Unpaid Principal Balance	118,766	159,890
Related Allowance	805	4,379
Other Commercial Construction [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	26,218	93,629
Unpaid Principal Balance	47,519	102,008
Related Allowance	900	4,022
Residential [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	105,785	180,652
Unpaid Principal Balance	134,093	209,879
Related Allowance	4,296	7,146
Residential Alt-A [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	127,889	140,268
Unpaid Principal Balance	161,529	176,739
Related Allowance	11,000	14,000
Home Equity Lines and Loans [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	19,771	13,672
Unpaid Principal Balance	20,806	14,796
Related Allowance	6,213	3,312
Automobile [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	30,317	40,441
Unpaid Principal Balance	30,317	40,441
Related Allowance	8,070	11,074
Other [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	18,973	17,660
Unpaid Principal Balance	18,973	17,660
Related Allowance	5,459	4,541
Impaired Financing Receivable With Related Allowance [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	498,575	603,626
Unpaid Principal Balance	581,887	702,000
Related Allowance	82,643	92,608
Impaired Financing Receivable With Related Allowance [Member] | Commercial, Financial, Leasing, etc. [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	132,340	90,293
Unpaid Principal Balance	165,146	112,092
Related Allowance	31,779	24,614
Impaired Financing Receivable With Related Allowance [Member] | Commercial Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	83,955	113,570
Unpaid Principal Balance	96,209	132,325
Related Allowance	14,121	19,520
Impaired Financing Receivable With Related Allowance [Member] | Residential Builder and Developer [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	17,632	33,311
Unpaid Principal Balance	22,044	55,122
Related Allowance	805	4,379
Impaired Financing Receivable With Related Allowance [Member] | Other Commercial Construction [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	5,480	86,260
Unpaid Principal Balance	6,484	90,515
Related Allowance	900	4,022
Impaired Financing Receivable With Related Allowance [Member] | Residential [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	88,970	96,508
Unpaid Principal Balance	107,343	114,521
Related Allowance	4,296	7,146
Impaired Financing Receivable With Related Allowance [Member] | Residential Alt-A [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	101,137	111,911
Unpaid Principal Balance	114,565	124,528
Related Allowance	11,000	14,000
Impaired Financing Receivable With Related Allowance [Member] | Home Equity Lines and Loans [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	19,771	13,672
Unpaid Principal Balance	20,806	14,796
Related Allowance	6,213	3,312
Impaired Financing Receivable With Related Allowance [Member] | Automobile [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	30,317	40,441
Unpaid Principal Balance	30,317	40,441
Related Allowance	8,070	11,074
Impaired Financing Receivable With Related Allowance [Member] | Other [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	18,973	17,660
Unpaid Principal Balance	18,973	17,660
Related Allowance	5,459	4,541
Impaired Financing Receivable with No Related Allowance [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	263,880	285,600
Unpaid Principal Balance	371,907	381,258
Impaired Financing Receivable with No Related Allowance [Member] | Commercial, Financial, Leasing, etc. [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	73,978	28,093
Unpaid Principal Balance	81,493	33,095
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	66,777	65,271
Unpaid Principal Balance	78,943	84,333
Impaired Financing Receivable with No Related Allowance [Member] | Residential Builder and Developer [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	58,820	72,366
Unpaid Principal Balance	96,722	104,768
Impaired Financing Receivable with No Related Allowance [Member] | Other Commercial Construction [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	20,738	7,369
Unpaid Principal Balance	41,035	11,493
Impaired Financing Receivable with No Related Allowance [Member] | Residential [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	16,815	84,144
Unpaid Principal Balance	26,750	95,358
Impaired Financing Receivable with No Related Allowance [Member] | Residential Alt-A [Member]
Schedule Of Financial Receivables [Line Items]
Recorded Investment	26,752	28,357
Unpaid Principal Balance	$46,964	$52,211

Allowance_for_Credit_Losses_In

Allowance for Credit Losses - Interest Income Recognized on Loans (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	$852,027	$1,001,641	$1,063,782
Interest Income Recognized, Total	27,799	35,560	29,419
Interest Income Recognized, Cash Basis	18,573	25,451	18,520
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	181,932	155,188	151,314
Interest Income Recognized, Total	2,251	7,197	2,938
Interest Income Recognized, Cash Basis	2,251	7,197	2,938
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	184,773	197,533	185,171
Interest Income Recognized, Total	4,029	4,852	2,834
Interest Income Recognized, Cash Basis	4,029	4,852	2,834
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	91,149	147,288	249,191
Interest Income Recognized, Total	142	1,043	1,563
Interest Income Recognized, Cash Basis	142	796	1,102
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	62,734	96,475	99,672
Interest Income Recognized, Total	1,893	5,248	5,020
Interest Income Recognized, Cash Basis	1,893	5,248	5,020
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	126,005	183,059	132,888
Interest Income Recognized, Total	9,180	6,203	5,284
Interest Income Recognized, Cash Basis	6,978	4,111	3,300
Residential Alt-A [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	133,800	149,461	171,546
Interest Income Recognized, Total	6,613	6,784	7,175
Interest Income Recognized, Cash Basis	2,546	2,341	2,226
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	18,083	12,811	11,322
Interest Income Recognized, Total	750	683	663
Interest Income Recognized, Cash Basis	248	183	179
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	35,173	44,116	51,650
Interest Income Recognized, Total	2,251	2,916	3,470
Interest Income Recognized, Cash Basis	295	515	724
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	18,378	15,710	11,028
Interest Income Recognized, Total	690	634	472
Interest Income Recognized, Cash Basis	$191	$208	$197

Allowance_for_Credit_Losses_Su

Allowance for Credit Losses - Summary of Loan Grades (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$66,668,956	$64,073,159
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	19,461,292	18,705,216
Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	18,695,440	17,894,592
Commercial, Financial, Leasing, etc. [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	588,407	699,885
Commercial, Financial, Leasing, etc. [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	177,445	110,739
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,556,939	21,741,858
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,837,022	20,972,257
Commercial [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	578,317	596,553
Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	141,600	173,048
Residential Builder and Developer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,465,140	1,276,512
Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,347,778	1,107,144
Residential Builder and Developer [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	45,845	72,941
Residential Builder and Developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	71,517	96,427
Other Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	3,545,490	3,129,838
Other Commercial Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	3,347,522	3,040,106
Other Commercial Construction [Member] | Criticized Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	172,269	54,464
Other Commercial Construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$25,699	$35,268

Allowance_for_Credit_Losses_Al

Allowance for Credit Losses - Allocation of Allowance for Credit Losses on Basis of Company's Impairment Methodology (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$81,714	$92,231
Allowance for credit losses	753,052	742,951
Allowance for credit losses	919,562	916,676	925,860	908,290
Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	9,142	6,479
Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	843,908	841,661
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	75,654	75,015
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	31,779	24,614
Allowance for credit losses	251,607	246,096
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	4,652	2,673
Commercial, Financial, Leasing, etc. [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	288,038	273,383
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	15,490	27,563
Allowance for credit losses	291,244	296,781
Commercial Real Estate [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	1,193	634
Commercial Real Estate [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	307,927	324,978
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	14,703	21,127
Allowance for credit losses	45,061	55,864
Residential Real Estate [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	2,146	1,665
Residential Real Estate [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	61,910	78,656
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	19,742	18,927
Allowance for credit losses	165,140	144,210
Consumer Loans [Member] | Purchased Impaired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	1,151	1,507
Consumer Loans [Member] | Allocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$186,033	$164,644

Allowance_for_Credit_Losses_Re

Allowance for Credit Losses - Recorded Investment in Loans and Leases on Basis of Company's Impairment Methodology (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$66,668,956	$64,073,159
Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	760,124	886,858
Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	65,711,095	62,855,509
Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	197,737	330,792
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	19,461,292	18,705,216
Commercial, Financial, Leasing, etc. [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	206,318	118,386
Commercial, Financial, Leasing, etc. [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	19,244,674	18,571,124
Commercial, Financial, Leasing, etc. [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,300	15,706
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	27,567,569	26,148,208
Commercial Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	252,347	376,339
Commercial Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	27,148,382	25,488,584
Commercial Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	166,840	283,285
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	8,657,301	8,928,221
Residential Real Estate [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	232,398	320,360
Residential Real Estate [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	8,406,680	8,578,677
Residential Real Estate [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	18,223	29,184
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,982,794	10,291,514
Consumer Loans [Member] | Individually Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	69,061	71,773
Consumer Loans [Member] | Collectively Evaluated for Impairment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,911,359	10,217,124
Consumer Loans [Member] | Purchased Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$2,374	$2,617

Premises_and_Equipment_Summary

Premises and Equipment - Summary of Premises and Equipment (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Land	$82,335	$84,220
Leasehold improvements	219,152	208,947
Premises and equipment, gross	1,314,422	1,261,890
Less: accumulated depreciation and amortization	701,438	628,370
Premises and equipment, net	612,984	633,520
Owned Assets [Member]
Property, Plant and Equipment [Line Items]
Buildings	406,522	402,065
Furniture and equipment	586,429	547,824
Less: accumulated depreciation and amortization	686,372	617,228
Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Buildings	1,131	1,131
Furniture and equipment	18,853	17,703
Less: accumulated depreciation and amortization	$15,066	$11,142

Premises_and_Equipment_Additio

Premises and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Net lease expense for all operating leases	$104,297,000	$103,297,000	$102,924,000

Capitalized_Servicing_Assets_C

Capitalized Servicing Assets - Changes in Capitalized Servicing Assets (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	$210,101	$172,976	$198,192
Originations	44,207	79,129	34,230
Purchases	1,019	272	109
Recognized in loan securitization transactions		23,078
Amortization	-68,410	-65,354	-59,555
Amortized value, ending balance	186,917	210,101	172,976
Valuation allowance		-300	-4,500
Ending balance, net	186,917	209,801	168,476
Other [Member]
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	11,225	8,143	15,678
Recognized in loan securitization transactions		9,382
Amortization	-7,118	-6,300	-7,535
Amortized value, ending balance	4,107	11,225	8,143
Ending balance, net	4,107	11,225	8,143
Residential Mortgage Loans [Member]
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	126,377	104,855	131,264
Originations	28,285	52,375	14,577
Purchases	289	272	109
Recognized in loan securitization transactions		13,696
Amortization	-45,080	-44,821	-41,095
Amortized value, ending balance	109,871	126,377	104,855
Valuation allowance		-300	-4,500
Ending balance, net	109,871	126,077	100,355
Commercial Mortgage Loans [Member]
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	72,499	59,978	51,250
Originations	15,922	26,754	19,653
Purchases	730
Amortization	-16,212	-14,233	-10,925
Amortized value, ending balance	72,939	72,499	59,978
Ending balance, net	$72,939	$72,499	$59,978

Capitalized_Servicing_Assets_A

Capitalized Servicing Assets - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Servicing Assets at Fair Value [Line Items]
Residential mortgage loans securitized formerly held in Company's portfolio		$1,300,000,000
Automobile loans securitized and sold	0	1,400,000,000
Residential Mortgage Loans [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	64,400,000,000	69,100,000,000	64,400,000,000	69,100,000,000	32,100,000,000
Estimated fair value of capitalized mortgage loan servicing assets	228,000,000	266,000,000	228,000,000	266,000,000
Weighted average discount rates used to estimate fair value of capitalized mortgaged loan servicing assets			11.90%	9.30%
Weighted-average option-adjusted spread in the discount rate			1065 basis points	770 basis points
Residential Mortgage Sub Servicing Loan [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	42,100,000,000	46,600,000,000	42,100,000,000	46,600,000,000	12,500,000,000
Commercial Mortgage Loans [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	11,300,000,000	11,400,000,000	11,300,000,000	11,400,000,000	10,600,000,000
Commercial Mortgage Loans [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	3,500,000,000	4,400,000,000	3,500,000,000	4,400,000,000	3,800,000,000
Estimated fair value of capitalized mortgage loan servicing assets	$87,000,000	$85,000,000	$87,000,000	$85,000,000
Weighted average discount rates used to estimate fair value of capitalized mortgaged loan servicing assets	18.00%	18.00%

Capitalized_Servicing_Assets_E

Capitalized Servicing Assets - Economic Assumptions Used to Determine Fair Value of Capitalized Servicing Rights and Sensitivity of Value to Changes in Assumptions (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Residential Mortgage Loans [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Weighted-average prepayment speeds	11.22%
Impact on fair value of 10% adverse change	($8,001,000)
Impact on fair value of 20% adverse change	-15,364,000
Weighted-average OAS	10.65%
Impact on fair value of 10% adverse change	-6,959,000
Impact on fair value of 20% adverse change	-13,492,000
Commercial Mortgage Loans [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Weighted-average discount rate	18.00%
Impact on fair value of 10% adverse change	-3,671,000
Impact on fair value of 20% adverse change	($7,092,000)

Recovered_Sheet2

Goodwill and Other Intangible Assets - Total Amortizing Intangible Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$933,062	$933,062
Accumulated Amortization	898,035	864,211
Net Carrying Amount	35,027	68,851
Core Deposit [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	755,794	755,794
Accumulated Amortization	730,188	705,518
Net Carrying Amount	25,606	50,276
Other [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	177,268	177,268
Accumulated Amortization	167,847	158,693
Net Carrying Amount	$9,421	$18,575

Recovered_Sheet3

Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill And Other Intangible Assets [Line Items]
Useful lives of core deposit and other intangible assets	8 years
Remaining weighted-average amortization period	2 years
Amortization of core deposit and other intangible assets	$33,824,000	$46,912,000	$60,631,000
Core Deposit and Other Intangible Assets [Member]
Goodwill And Other Intangible Assets [Line Items]
Amortization of core deposit and other intangible assets	$33,824,000	$46,912,000	$60,631,000
Minimum [Member]
Goodwill And Other Intangible Assets [Line Items]
Useful lives of core deposit and other intangible assets	5 years
Maximum [Member]
Goodwill And Other Intangible Assets [Line Items]
Useful lives of core deposit and other intangible assets	10 years

Goodwill_and_Other_Intangible_2

Goodwill and Other Intangible Assets - Estimated Amortization Expense in Future Years (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
2015	$20,938
2016	10,052
2017	3,303
2018	734
Future Amortization Expense, Total	$35,027	$68,851

Goodwill_and_Other_Intangible_3

Goodwill and Other Intangible Assets - Summary of Goodwill Assigned to Reportable Segments for Purposes of Testing for Impairment (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill [Line Items]
Goodwill	$3,524,625	$3,524,625
Business Banking [Member]
Goodwill [Line Items]
Goodwill	748,907	748,907
Commercial Banking [Member]
Goodwill [Line Items]
Goodwill	907,524	907,524
Commercial Real Estate [Member]
Goodwill [Line Items]
Goodwill	349,197	349,197
Retail Banking [Member]
Goodwill [Line Items]
Goodwill	1,144,404	1,144,404
All Other [Member]
Goodwill [Line Items]
Goodwill	$374,593	$374,593

Borrowings_Amounts_and_Interes

Borrowings - Amounts and Interest Rates of Short-term Borrowings (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Borrowings [Line Items]
Federal Funds Purchased and Repurchase Agreements	$192,676	$260,455
Federal funds purchased and short term borrowings	192,676	260,455	1,074,482
Weighted-average interest rate	0.07%	0.04%	0.11%
Daily-average amount outstanding	214,736	390,034	838,902
Weighted-average interest rate	0.05%	0.11%	0.15%
Federal Funds Purchased and Repurchase Agreements [Member]
Schedule Of Borrowings [Line Items]
Federal Funds Purchased and Repurchase Agreements	192,676	260,455	1,074,482
Weighted-average interest rate	0.07%	0.04%	0.11%
Highest amount at a month-end	280,350	563,879	1,224,194
Daily-average amount outstanding	214,736	390,034	822,859
Weighted-average interest rate	0.05%	0.11%	0.15%
Other Short-term Borrowings [Member]
Schedule Of Borrowings [Line Items]
Other Short-term borrowings	0	0	0
Highest amount at a month-end			50,016
Daily-average amount outstanding			$16,043
Weighted-average interest rate			0.57%

Borrowings_Lines_of_Credit_Und

Borrowings - Lines of Credit Under Formal Agreements (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
M&T Bank [Member]
Schedule Of Borrowings [Line Items]
Outstanding borrowings	$1,161,475
Unused	19,825,036
Wilmington Trust, N.A. [Member]
Schedule Of Borrowings [Line Items]
Unused	$275,414

Borrowings_Additional_Informat

Borrowings - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2014
Schedule Of Borrowings [Line Items]
Minimum variable interest rate of Junior Subordinated Debentures	1.08%	1.09%
Maximum variable interest rate of Junior Subordinated Debentures	3.58%	3.59%
Interest rate payable on Junior Subordinated Debentures	1.66%	1.67%
Minimum contractual interest rates of long-term agreements to repurchase securities	3.61%	3.61%
Maximum contractual interest rates of long-term agreements to repurchase securities	4.30%	4.30%
Weighted-average contractual interest rates of long term agreements to repurchase securities	3.90%	3.90%
Repurchase dates of the long-term agreements outstanding	2017
Collateralized Financings	$1,500,000,000	$1,600,000,000
Trust preferred capital securities	25.00%
Junior Subordinated Debentures			350,000,000
Interest rate of debt instrument			8.50%
Debt Maturity, Start Year	1-Jan-27
Debt Maturity, End Year	31-Dec-33
M&T Bank [Member]
Schedule Of Borrowings [Line Items]
Borrowing facilities available with FHLB's amount	8,100,000,000
Federal Reserve Bank of New York [Member]
Schedule Of Borrowings [Line Items]
Line of credit facility	$13,100,000,000
Long-term Fixed Rate Advances From FHLB [Member]
Schedule Of Borrowings [Line Items]
Variable contractual interest rate of long-term debt lower limit	1.17%	3.48%
Variable contractual interest rate of long-term debt upper limit	7.32%	7.32%
Weighted-average contractual variable interest rate	1.68%	4.60%
Advances from the FHLB maturity date	2035
Floating Rate Senior Notes [Member]
Schedule Of Borrowings [Line Items]
Minimum variable interest rate of Junior Subordinated Debentures	0.54%
Maximum variable interest rate of Junior Subordinated Debentures	0.61%
Interest rate payable on Junior Subordinated Debentures		0.54%
Weighted-average contractual interest rate payable	0.56%

Borrowings_Longterm_Borrowings

Borrowings - Long-term Borrowings (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2014
Schedule Of Borrowings [Line Items]
Fixed rates	$1,161,514	$29,079
Agreements to repurchase securities	1,400,000	1,400,000
Junior subordinated debentures associated with preferred capital securities			350,000
Other	23,011	30,257
Long-term borrowings	9,006,959	5,108,870
Variable Rate Notes Due 2016 [Member]
Schedule Of Borrowings [Line Items]
Variable rates	300,000	300,000
Variable Rate Term Loans Due 2017 [Member]
Schedule Of Borrowings [Line Items]
Variable rates	550,000
1.25% Due 2017 [Member]
Schedule Of Borrowings [Line Items]
Variable rates	499,969
1.40% Due 2017 [Member]
Schedule Of Borrowings [Line Items]
Variable rates	749,756
1.45% Due 2018 [Member]
Schedule Of Borrowings [Line Items]
Variable rates	503,118	502,479
2.25% Due 2019 [Member]
Schedule Of Borrowings [Line Items]
Variable rates	648,243
2.30% Due 2019 [Member]
Schedule Of Borrowings [Line Items]
Variable rates	748,965
8.5% due 2018 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	218,883	224,067
6.625% due 2017 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	428,627	437,582
9.5% due 2018 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes		50,000
5.585% due 2020, Variable Rate Commencing 2015 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	400,846	392,964
5.629% due 2021, Variable Rate Commencing 2016 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	538,961	559,378
M&T Capital Trust I - 8.234%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	154,640	154,640
M&T Capital Trust II - 8.277%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	103,093	103,093
M&T Capital Trust III - 9.25%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	65,784	66,109
BSB Capital Trust I - 8.125%, due 2028 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	15,612	15,589
Provident Trust I - 8.29%, due 2028 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	25,405	25,051
Southern Financial Statutory Trust I - 10.60%, due 2030 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	6,550	6,521
M&T Capital Trust IV - 8.50%, due 2068 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities		350,010
First Maryland Capital I - due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	145,179	144,641
First Maryland Capital II - due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	146,627	145,964
Allfirst Asset Trust - due 2029 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	96,204	96,059
BSB Capital Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	15,464	15,464
Provident Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	52,692	52,176
Southern Financial Capital Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	$7,816	$7,747

Borrowings_Longterm_Borrowings1

Borrowings - Long-term Borrowings (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2014
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument			8.50%
Debt Maturity, Start Date	1-Jan-27
Debt Maturity, End Date	31-Dec-33
Variable Rate Due 2016 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2016	2016
Senior Notes Due 2017 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2017	2017
1.25% Due 2017 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	1.25%	1.25%
Debt maturity date	2017	2017
1.40% Due 2017 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	1.40%	1.40%
Debt maturity date	2017	2017
1.45% Due 2018 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	1.45%	1.45%
Debt maturity date	2018	2018
2.25% Due 2019 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	2.25%	2.25%
Debt maturity date	2019	2019
2.30% Due 2019 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	2.30%	2.30%
Debt maturity date	2019	2019
8.5% due 2018 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.50%	8.50%
Debt maturity date	2018	2018
6.625% due 2017 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	6.63%	6.63%
Debt maturity date	2017	2017
9.5% due 2018 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	9.50%	9.50%
Debt maturity date	2018	2018
5.585% due 2020, Variable Rate Commencing 2015 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	5.59%	5.59%
Debt Maturity, Start Date	1-Jan-15	1-Jan-15
Debt Maturity, End Date	31-Dec-20	31-Dec-20
5.629% due 2021, Variable Rate Commencing 2016 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	5.63%	5.63%
Debt Maturity, Start Date	1-Jan-16	1-Jan-16
Debt Maturity, End Date	31-Dec-21	31-Dec-21
M&T Capital Trust I - 8.234%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.23%	8.23%
Debt maturity date	2027	2027
M&T Capital Trust II - 8.277%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.28%	8.28%
Debt maturity date	2027	2027
M&T Capital Trust III - 9.25%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	9.25%	9.25%
Debt maturity date	2027	2027
BSB Capital Trust I - 8.125%, due 2028 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.13%	8.13%
Debt maturity date	2028	2028
Provident Trust I - 8.29%, due 2028 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.29%	8.29%
Debt maturity date	2028	2028
Southern Financial Statutory Trust I - 10.60%, due 2030 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	10.60%	10.60%
Debt maturity date	2030	2030
M&T Capital Trust IV - 8.50%, due 2068 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.50%	8.50%
Debt maturity date	2068	2068
First Maryland Capital I - due 2027 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2027	2027
First Maryland Capital II - due 2027 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2027	2027
Allfirst Asset Trust - due 2029 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2029	2029
BSB Capital Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2033	2033
Provident Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2033	2033
Southern Financial Capital Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Debt maturity date	2033	2033

Borrowings_Maturity_of_Longter

Borrowings - Maturity of Long-term Borrowings (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt Disclosure [Abstract]
2015	$6,444
2016	1,105,540
2017	3,407,786
2018	723,516
2019	1,971,842
Later years	1,791,831
Long-term borrowings	$9,006,959	$5,108,870

Shareholders_Equity_Additional

Shareholders' Equity - Additional Information (Detail) (USD $)	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Preferred stock, shares authorized	1,000,000	1,000,000	1,000,000
Preferred stock, par value	$1	$1	$1
Warrant [Member] | Series D Fixed Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Exercise price of each class of warrants or rights outstanding	$518.96		$518.96
Warrant to purchase common stock	95,383		95,383

Shareholders_Equity_Issued_and

Shareholders' Equity - Issued and Outstanding Preferred Stock (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Class of Stock [Line Items]
Carrying value	$1,231,500	$881,500
Series D Fixed 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
Series E Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	350,000
Preferred stock, shares outstanding	350,000
Carrying value	350,000
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

Shareholders_Equity_Issued_and1

Shareholders' Equity - Issued and Outstanding Preferred Stock (Parenthetical) (Detail) (USD $)	12 Months Ended		1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Series D Fixed Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$10,000	10,000
Preferred stock dividend rate	6.88%
Preferred Stock, Redemption Feature, Redemption Term	90 days
Preferred shares redemption date	15-Jun-16
Series E Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$1,000	1,000
Preferred stock dividend rate	6.45%
Date of change in the dividend rate	14-Feb-24
Preferred Stock, Redemption Feature, Redemption Term	90 days
Preferred shares redemption date	15-Feb-24
London Interbank offered rate plus basis points	3.61%
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$1,000	1,000
Exercise of warrants into shares of common stock	1,218,522
Exercise price of each class of warrants or rights outstanding	$73.86
Date of change in the dividend rate	14-Nov-13
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate up to November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	5.00%
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate Thereafter November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	6.38%
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Warrant [Member]
Class of Stock [Line Items]
Warrants and rights outstanding	721,490
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Warrant [Member] | Cash Less Exercise [Member]
Class of Stock [Line Items]
Exercise of warrants into shares of common stock	427,905	69,127
Issuance of common shares	169,543	25,427
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Liquidation preference	$1,000	1,000
Exercise of warrants into shares of common stock	407,542
Exercise price of each class of warrants or rights outstanding	$55.76
Date of change in the dividend rate	14-Nov-13
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate up to November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	5.00%
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Dividend Paid Rate Thereafter November 14, 2013 [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	6.38%
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member] | Warrant [Member]
Class of Stock [Line Items]
Issuance of common shares			186,589

Recovered_Sheet4

Stock-Based Compensation Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$65,000,000	$55,000,000	$57,000,000
Recognized income tax benefits related to stock-based compensation	31,000,000	29,000,000	30,000,000
Shares under equity incentive compensation plan for future grant	4,398,496	4,874,542
Directors Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issuable under deferred compensation plans	12,033	14,185
Shares issued in connection with deferred compensation plans	211,655
Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	85,761	0	151,014
Common stock authorized for issuance	2,500,000
Cash received from exercise of stock options	8,607,000		10,117,000
Stock Option Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Stock options exercisable period, maximum	10 years 1 day
Cash realized from exercise of stock options	127,000,000	172,000,000	153,000,000
Tax benefits realized from exercise of stock options	9,000,000	12,000,000	8,000,000
Intrinsic value of stock options exercised	26,000,000	34,000,000	21,000,000
Total grant date fair value of stock options vested			17,000,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years	4 years
Unrecognized compensation cost expected to be recognized over a weighted-average period (in years)	1 year
Unrecognized compensation cost related to non-vested awards	19,000,000
Shares issued	221,822	269,755	453,908
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value	24,765,000	27,716,000	36,969,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to non-vested awards	7,000,000
Shares issued	299,525	315,316	278,505
Weighted-average grant date fair value	$33,406,000	$32,380,000	$22,139,000
Deferred Bonus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issuable under deferred compensation plans	29,297	33,046

StockBased_Compensation_Plans_1

Stock-Based Compensation Plans - Summary of Restricted Stock and Restricted Stock Unit Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Outstanding, Unvested, Beginning balance	770,830
Restricted Stock Outstanding, Granted	299,525
Restricted Stock Outstanding, Vested	-279,747
Restricted Stock Outstanding, Cancelled	-1,197
Restricted Stock Outstanding, Unvested, Ending balance	789,411
Weighted-Average Grant Price, Unvested, Beginning balance	$89.58
Weighted-Average Grant Price, Granted	$111.53
Weighted-Average Grant Price, Vested	$84.95
Weighted-Average Grant Price, Cancelled	$103.25
Weighted-Average Grant Price, Unvested, Ending balance	$99.53
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Outstanding, Unvested, Beginning balance	862,695
Restricted Stock Outstanding, Granted	221,822
Restricted Stock Outstanding, Vested	-295,438
Restricted Stock Outstanding, Cancelled	-27,434
Restricted Stock Outstanding, Unvested, Ending balance	761,645
Weighted-Average Grant Price, Unvested, Beginning balance	$87.29
Weighted-Average Grant Price, Granted	$111.64
Weighted-Average Grant Price, Vested	$81.32
Weighted-Average Grant Price, Cancelled	$96.70
Weighted-Average Grant Price, Unvested, Ending balance	$96.36

StockBased_Compensation_Plans_2

Stock-Based Compensation Plans - Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Options Outstanding, Beginning balance	4,880,761
Stock Options Outstanding, Granted	200
Stock Options Outstanding, Exercised	-1,372,113
Stock Options Outstanding, Expired	-75,978
Stock Options Outstanding, Ending balance	3,432,870
Stock Options Outstanding, Exercisable	3,432,470
Weighted-Average Exercise Price, Outstanding, Beginning balance	$105.48
Weighted-Average Exercise Price, Granted	$111.51
Weighted-Average Exercise Price, Exercised	$101.55
Weighted-Average Exercise Price, Expired	$184.15
Weighted-Average Exercise Price, Outstanding, Ending balance	$105.31
Weighted-Average Exercise Price, Exercisable	$105.31
Weighted-Average Life (In Years), Outstanding, Ending balance	2 years 1 month 6 days
Weighted-Average Life (In Years), Exercisable	2 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding, Ending balance	$71,418
Aggregate Intrinsic Value, Exercisable	$71,408

Recovered_Sheet5

Pension Plans and Other Postretirement Benefits - Net Periodic Benefit Cost for Defined Benefit Plans (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$20,520	$24,360	$29,549
Interest cost on benefit obligation	69,162	60,130	62,037
Expected return on plan assets	-91,568	-87,353	-70,511
Amortization of prior service cost (credit)	-6,552	-6,556	-6,559
Recognized net actuarial loss	14,494	41,076	37,386
Net periodic benefit costs	6,056	31,657	51,902
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	605	742	668
Interest cost on benefit obligation	2,778	2,691	3,737
Amortization of prior service cost (credit)	-1,359	-1,359	21
Recognized net actuarial loss		360	530
Net periodic benefit costs	$2,024	$2,434	$4,956

Recovered_Sheet6

Pension Plans and Other Postretirement Benefits - Data Relating to Funding Position of Defined Benefit Plans (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at end of year	$1,503,614,000	$1,504,691,000
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	1,484,193,000	1,644,567,000
Service cost	20,520,000	24,360,000	29,549,000
Interest cost	69,162,000	60,130,000	62,037,000
Amendments	4,619,000
Actuarial (gain) loss	300,444,000	-184,181,000
Benefits paid	-65,529,000	-60,683,000
Benefit obligation at end of year	1,813,409,000	1,484,193,000	1,644,567,000
Fair value of plan assets at beginning of year	1,506,684,000	1,408,771,000
Actual return on plan assets	56,430,000	150,795,000
Employer contributions	8,076,000	7,801,000
Benefits and other payments	-65,529,000	-60,683,000
Fair value of plan assets at end of year	1,505,661,000	1,506,684,000	1,408,771,000
Funded status	-307,748,000	22,491,000
Net prepaid asset		139,576,000
Accrued liabilities	-307,748,000	-117,085,000
Net loss (gain)	512,473,000	191,386,000
Net prior service cost	-5,728,000	-16,899,000
Pre-tax adjustment to AOCI	506,745,000	174,487,000
Taxes	-198,897,000	-68,486,000
Net adjustment to AOCI	307,848,000	106,001,000
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	60,592,000	74,966,000
Service cost	605,000	742,000	668,000
Interest cost	2,778,000	2,691,000	3,737,000
Plan participants' contributions	3,498,000	3,069,000
Actuarial (gain) loss	7,793,000	-12,830,000
Medicare Part D reimbursement	495,000	509,000
Benefits paid	-8,259,000	-8,555,000
Benefit obligation at end of year	67,502,000	60,592,000	74,966,000
Employer contributions	4,266,000	4,977,000
Plan participants' contributions	3,498,000	3,069,000
Medicare Part D reimbursement	495,000	509,000
Benefits and other payments	-8,259,000	-8,555,000
Funded status	-67,502,000	-60,592,000
Accrued liabilities	-67,502,000	-60,592,000
Net loss (gain)	6,737,000	-1,056,000
Net prior service cost	-10,455,000	-11,814,000
Pre-tax adjustment to AOCI	-3,718,000	-12,870,000
Taxes	1,459,000	5,051,000
Net adjustment to AOCI	($2,259,000)	($7,819,000)

Pension_Plans_and_Other_Postre2

Pension Plans and Other Postretirement Benefits - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Minimum pension liability	$503,027,000
Minimum pension liability adjustment net of tax	305,589,000
Discount rate	4.00%	4.75%
Increase in minimum liability adjustment		341,410,000
Decrease in minimum pension liability adjustment net of tax		207,407,000
Defined contribution pension and retirement savings plans total expense	22,000,000	21,000,000	17,000,000
Annual rate of increase in health care cost assumed for next fiscal year	7.00%
Defined Benefit Plan, ultimate health care cost trend rate	5.00%
Period for decreasing the annual rate	Over 28 years
Defined benefit pension plans	172,026,000
Percentage of total assets	11.40%
Defined benefit plan fair value of plan assets	1,503,614,000	1,504,691,000
Percentage of pension plan assets that is not exceeded by investment in security of single Non-US Government of Government agency	10.00%
Qualified benefit pension plans	0	0
Percentage of eligible employees contribution for Retirement Savings Plan	50.00%
Percentage of employer matching contribution to employee's contribution	75.00%
Maximum employer contribution on Employee's qualified contribution	4.50%
Qualified defined contribution plans expense during the period	32,466,000	31,797,000	31,305,000
Total Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target allocations for plan assets, minimum range	45.00%
Target allocations for plan assets, maximum range	80.00%
Defined benefit plan fair value of plan assets	1,071,467,000	1,045,995,000
Total Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target allocations for plan assets, minimum range	5.00%
Target allocations for plan assets, maximum range	40.00%
Defined benefit plan fair value of plan assets	230,663,000	252,704,000
Other Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target allocations for plan assets, minimum range	5.00%
Target allocations for plan assets, maximum range	30.00%
Defined benefit plan fair value of plan assets	172,026,000	168,040,000
M&T Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	154,252,000	142,955,000
Percentage of common stock in total plan assets	10.20%	9.50%
Supplemental Pension Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Projected benefit obligation	135,891,000
Accumulated benefit obligation		117,085,000
Employer contributions	8,076,000	7,801,000
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Projected benefit obligation	1,813,409,000	1,484,193,000	1,644,567,000
Accumulated benefit obligation	1,782,387,000	1,460,498,000
Minimum pension liability	506,745,000
Discount rate	4.75%	3.75%	4.25%
Defined benefit plan fair value of plan assets	1,505,661,000	1,506,684,000	1,408,771,000
Employer contributions	8,076,000	7,801,000
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Projected benefit obligation	67,502,000	60,592,000	74,966,000
Minimum pension liability	-3,718,000
Discount rate	4.75%	3.75%	4.25%
Employer contributions	$4,266,000	$4,977,000

Pension_Plans_and_Other_Postre3

Pension Plans and Other Postretirement Benefits - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	$343,374	($260,452)
Prior service cost	4,619
Amortization of prior service credit	7,911	7,915	6,538
Amortization of loss	-14,494	-41,436	-37,916
Total recognized in other comprehensive income, pre-tax	341,410	-293,973
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	335,581	-247,622
Prior service cost	4,619
Amortization of prior service credit	6,552	6,556
Amortization of loss	-14,494	-41,076
Total recognized in other comprehensive income, pre-tax	332,258	-282,142
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	7,793	-12,830
Amortization of prior service credit	1,359	1,359
Amortization of loss		-360
Total recognized in other comprehensive income, pre-tax	$9,152	($11,831)

Recovered_Sheet7

Pension Plans and other Postretirement Benefits - Amortization of Amounts in Accumulated Other Comprehensive Income Expected to be Recognized as Components of Net Periodic Benefit Expense (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Amortization of net prior service credit	($6,005)
Amortization of net loss	44,653
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Amortization of net prior service credit	-1,359
Amortization of net loss	$91

Pension_Plans_and_Other_Postre4

Pension Plans and Other Postretirement Benefits - Assumed Weighted-Average Rates Used to Determine Benefit Obligations (Detail)	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.00%	4.75%
Rate of increase in future compensation levels	4.39%	4.42%
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.00%	4.75%

Pension_Plans_and_Other_Postre5

Pension Plans and Other Postretirement Benefits - Assumed Weighted-Average Rates Used to Determine Net Benefit Expense (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.00%	4.75%
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.75%	3.75%	4.25%
Long-term rate of return on plan assets	6.50%	6.50%	6.50%
Rate of increase in future compensation levels	4.42%	4.50%	4.50%
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.75%	3.75%	4.25%

Pension_Plans_and_Other_Postre6

Pension Plans and Other Postretirement Benefits - Effects on One-Percentage Point Change in Assumed Health Care Cost Trend Rates (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Service and interest cost	$97
Accumulated postretirement benefit obligation	3,005
Service and interest cost	-88
Accumulated postretirement benefit obligation	($2,678)

Pension_Plans_and_Other_Postre7

Pension Plans and Other Postretirement Benefits - Fair Values of Company's Pension Plan Assets by Asset Category (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	$1,503,614	$1,504,691
Money-Market Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	29,458	37,952
M&T Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	154,252	142,955
Domestic Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	214,127	271,203
International Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	16,170	24,053
Domestic Mutual Fund Equity securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	305,817	194,099
International Mutual Fund Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	381,101	413,685
Total Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	1,071,467	1,045,995
Corporate Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	102,848	63,196
Government Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	92,772	75,043
Domestic Mutual Fund Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	27,847	68,280
International Mutual Fund Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets		43,742
Total Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	230,663	252,704
Other Diversified Mutual Fund [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	96,936	93,055
Other Private Real Estate [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	2,162	3,123
Other Private Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	6,234	6,199
Other Hedge Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	66,694	65,663
Other Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	172,026	168,040
International Debt securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	7,196	2,443
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	1,268,138	1,330,513
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money-Market Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	29,458	37,952
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | M&T Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	154,252	142,955
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	214,127	271,203
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | International Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	16,170	24,053
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Mutual Fund Equity securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	305,817	194,099
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | International Mutual Fund Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	381,101	413,685
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	1,071,467	1,045,995
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Mutual Fund Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	27,847	68,280
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | International Mutual Fund Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets		43,742
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	27,847	112,022
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Diversified Mutual Fund [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	96,936	93,055
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Hedge Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	42,430	41,489
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	139,366	134,544
Significant Observable Inputs (Level 2) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	202,816	140,682
Significant Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	102,848	63,196
Significant Observable Inputs (Level 2) [Member] | Government Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	92,772	75,043
Significant Observable Inputs (Level 2) [Member] | Total Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	202,816	140,682
Significant Observable Inputs (Level 2) [Member] | International Debt securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	7,196	2,443
Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	32,660	33,496
Significant Unobservable Inputs (Level 3) [Member] | Other Private Real Estate [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	2,162	3,123
Significant Unobservable Inputs (Level 3) [Member] | Other Private Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	6,234	6,199
Significant Unobservable Inputs (Level 3) [Member] | Other Hedge Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	24,264	24,174
Significant Unobservable Inputs (Level 3) [Member] | Other Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined benefit plan fair value of plan assets	$32,660	$33,496

Pension_Plans_and_Other_Postre8

Pension Plans and Other Postretirement Benefits - Fair Values of Company's Pension Plan Assets by Asset Category (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Interest and dividend receivable on plan assets	$2,047,000	$1,993,000
Investment Grade Bonds of U.S. Issuers [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Investment in mutual funds	55.00%	35.00%
High-Yielding Bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Investment in mutual funds	45.00%	65.00%

Pension_Plans_and_Other_Postre9

Pension Plans and Other Postretirement Benefits - Changes in Level 3 Pension Plan Assets Measured at Fair Value on Recurring Basis (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year		$1,504,691
Fair value of plan assets at end of year	1,503,614	1,504,691
Other Private Real Estate [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year		3,123
Fair value of plan assets at end of year	2,162	3,123
Other Private Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year		6,199
Fair value of plan assets at end of year	6,234	6,199
Other Hedge Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year		65,663
Fair value of plan assets at end of year	66,694	65,663
Other Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year		168,040
Fair value of plan assets at end of year	172,026	168,040
Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year		33,496
Fair value of plan assets at end of year	32,660	33,496
Significant Unobservable Inputs (Level 3) [Member] | Other Private Real Estate [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	3,123
Sales	-1,167
Total Realized/Unrealized Gains	206
Fair value of plan assets at end of year	2,162
Significant Unobservable Inputs (Level 3) [Member] | Other Private Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	6,199
Sales	-905
Total Realized/Unrealized Gains	940
Fair value of plan assets at end of year	6,234
Significant Unobservable Inputs (Level 3) [Member] | Other Hedge Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	24,174
Sales	-513
Total Realized/Unrealized Gains	603
Fair value of plan assets at end of year	24,264
Significant Unobservable Inputs (Level 3) [Member] | Other Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	33,496
Sales	-2,585
Total Realized/Unrealized Gains	1,749
Fair value of plan assets at end of year	$32,660

Recovered_Sheet8

Pension Plans and Other Postretirement Benefits - Defined Benefit Plan Estimated Future Benefit Payments (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
2015	$70,107
2016	73,169
2017	77,294
2018	81,231
2019	87,027
2020 through 2024	497,177
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
2015	5,830
2016	5,719
2017	5,554
2018	5,412
2019	5,281
2020 through 2024	$24,190

Income_Taxes_Components_of_Inc

Income Taxes - Components of Income Tax Expense (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current
Federal	$378,978	$371,249	$309,156
State and city	50,790	68,035	82,014
Total current	429,768	439,284	391,170
Deferred
Federal	65,503	106,537	117,229
State and city	27,345	33,248	14,629
Total deferred	92,848	139,785	131,858
Income taxes	$522,616	$579,069	$523,028

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	State
Income Tax Disclosure [Abstract]
Tax bad debt reserve	$79,121,000
Income taxes attributable to gains or losses on bank investment securities	0	18,313,000	-18,766,000
Minimum alternative tax expense recognized for gains or losses on bank investment securities	$0	$0	$0
Number of state and local jurisdictions where company files income tax returns	40

Income_Taxes_Schedule_of_Incom

Income Taxes - Schedule of Income Taxes Expenses Benefit Reconciliation (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income taxes at statutory federal income tax rate	$556,102	$601,142	$543,384
Increase (decrease) in taxes:
Tax-exempt income	-31,752	-34,747	-33,890
State and city income taxes, net of federal income tax effect	50,788	65,834	62,818
Low income housing and other credits	-49,526	-49,206	-42,074
Other	-2,996	-3,954	-7,210
Income taxes	$522,616	$579,069	$523,028

Income_Taxes_Deferred_Tax_Asse

Income Taxes - Deferred Tax Assets (Liabilities) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Income Tax Disclosure [Abstract]
Losses on loans and other assets	$605,273	$645,713	$809,033
Postretirement and other employee benefits	34,052	30,023	34,517
Incentive compensation plans	36,450	37,772	50,067
Interest on loans	79,147	100,725	72,278
Retirement benefits	120,222		91,980
Stock-based compensation	64,017	63,101	69,874
Depreciation and amortization	3,527	1,404	12,130
Other	100,999	121,561	103,027
Gross deferred tax assets	1,043,687	1,000,299	1,242,906
Leasing transactions	-280,596	-284,370	-291,524
Unrealized investment gains	-82,065	-21,779	-23,574
Capitalized servicing rights	-46,393	-46,041	-20,348
Interest on subordinated note exchange	-3,125	-6,075	-8,794
Retirement benefits		-9,397
Other	-63,814	-49,450	-61,410
Gross deferred tax liabilities	-475,993	-417,112	-405,650
Net deferred tax asset	$567,694	$583,187	$837,256

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Federal, State and Local Tax [Member]
Reconciliation Of Unrecognized Tax Benefits [Line Items]
Beginning Balance	$14,611	$16,548	$18,333
Increases in unrecognized tax benefits as a result of tax positions taken during the period	769	2,267	860
Decreases in unrecognized tax benefits as a result of settlements with taxing authorities	-4,668	-1,854	-1,002
Decreases in unrecognized tax benefits because applicable returns are no longer subject to examination		-2,350	-1,643
Ending Balance	10,712	14,611	16,548
Accrued Interest [Member]
Reconciliation Of Unrecognized Tax Benefits [Line Items]
Beginning Balance	14,696	12,379	9,277
Increases in unrecognized tax benefits as a result of tax positions taken in prior years	453	4,429	4,514
Decreases in unrecognized tax benefits as a result of settlements with taxing authorities	-11,280	-487
Decreases in unrecognized tax benefits because applicable returns are no longer subject to examination		-1,625	-1,412
Ending Balance	3,869	14,696	12,379
Unrecognized Income Tax Benefits [Member]
Reconciliation Of Unrecognized Tax Benefits [Line Items]
Beginning Balance	29,307	28,927	27,610
Increases in unrecognized tax benefits as a result of tax positions taken during the period	769	2,267	860
Increases in unrecognized tax benefits as a result of tax positions taken in prior years	453	4,429	4,514
Decreases in unrecognized tax benefits as a result of settlements with taxing authorities	-15,948	-2,341	-1,002
Decreases in unrecognized tax benefits because applicable returns are no longer subject to examination		-3,975	-3,055
Ending Balance	14,581	29,307	28,927
Less: Federal, state and local income tax benefits	-5,103
Net unrecognized tax benefits that, if recognized, would impact the effective income tax rate	$9,478

Earnings_Per_Common_Share_Comp

Earnings Per Common Share - Computations of Basic Earnings Per Common Share (Detail) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income available to common shareholders:
Net income	$1,066,246	$1,138,480	$1,029,498
Less: Preferred stock dividends	-75,878	-54,120	-53,450
Amortization of preferred stock discount		-7,942	-8,026
Net income available to common equity	990,368	1,076,418	968,022
Less: Income attributable to unvested stock-based compensation awards	-11,837	-13,989	-14,632
Net income available to common shareholders	$978,531	$1,062,429	$953,390
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	132,532	130,354	127,793
Less: Unvested stock-based compensation awards	-1,582	-1,700	-1,929
Weighted-average shares outstanding	130,950	128,654	125,864
Basic earnings per common share	$7.47	$8.26	$7.57

Earnings_Per_Common_Share_Comp1

Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income available to common equity	$990,368	$1,076,418	$968,022
Less: Income attributable to unvested stock-based compensation awards	-11,787	-13,922	-14,593
Net income available to common shareholders	$978,581	$1,062,496	$953,429
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	132,532	130,354	127,793
Less: Unvested stock-based compensation awards	-1,582	-1,700	-1,929
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	894	949	541
Adjusted weighted-average shares outstanding	131,844	129,603	126,405
Diluted earnings per common share	$7.42	$8.20	$7.54

Earnings_Per_Common_Share_Addi

Earnings Per Common Share - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	2,017,000	3,847,000	8,905,000

Comprehensive_Income_Component

Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	($105,797)	($395,657)	($586,769)
Unrealized holding gains (losses), net	150,187	-51,834	134,923
Foreign currency translation adjustment	-4,039	546	809
Unrealized losses on cash flow hedges	-165
Unrealized losses on cash flow hedges	65
Unrealized losses on cash flow hedges	-100
Current year benefit plans gains (losses)	-347,993	260,452	-29,823
Total other comprehensive income (loss) before reclassifications	-202,010	209,164	105,909
OTTI charges recognized in net income		9,800	47,822
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	3,374	4,287	6,190
Losses (gains) realized in net income		33,088	-9
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	7		-178
Amortization of prior service credit	-7,911	-7,915	-6,538
Amortization of actuarial losses	14,494	41,436	37,916
Total reclassifications	9,964	80,696	85,203
Total gain (loss) during the period	-192,046	289,860	191,112
Beginning balance	41,638	155,393	230,328
Ending balance	-297,843	-105,797	-395,657
Unrealized holding gains (losses), net	-58,962	20,311	-52,905
Foreign currency translation adjustment	1,432	-165	-290
Current year benefit plans gains (losses)	136,587	-102,227	11,705
Total other comprehensive income (loss) before reclassifications	79,122	-82,081	-41,490
OTTI charges recognized in net income		-3,847	-18,770
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	-1,324	-1,683	-2,430
Losses (gains) realized in net income		-12,987	4
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	-3		66
Amortization of prior service credit	3,105	3,107	2,566
Amortization of actuarial losses	-5,689	-16,264	-14,881
Total reclassifications	-3,911	-31,674	-33,445
Total gain (loss) during the period	75,211	-113,755	-74,935
Beginning balance	-64,159	-240,264	-356,441
Ending balance	116,849	41,638	155,393
Unrealized holding gains (losses), net	91,225	-31,523	82,018
Foreign currency translation adjustment	-2,607	381	519
Current year benefit plans gains (losses)	-211,406	158,225	-18,118
Total other comprehensive income (loss) before reclassifications	-122,888	127,083	64,419
OTTI charges recognized in net income		5,953	29,052
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	2,050	2,604	3,760
Losses (gains) realized in net income		20,101	-5
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	4		-112
Amortization of prior service credit	-4,806	-4,808	-3,972
Amortization of actuarial losses	8,805	25,172	23,035
Total reclassifications	6,053	49,022	51,758
Total gain (loss) during the period	-116,835	176,105	116,177
Ending balance	-180,994	-64,159	-240,264
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	115	-431	-1,062
Foreign currency translation adjustment	-4,039	546	809
Unrealized losses on cash flow hedges	-165
Total other comprehensive income (loss) before reclassifications	-4,204	546	809
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	7		-178
Total reclassifications	7		-178
Total gain (loss) during the period	-4,197	546	631
Ending balance	-4,082	115	-431
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	37,255	-91,835	-138,319
Unrealized holding gains (losses), net	-29,818	77,794	-2,998
Total other comprehensive income (loss) before reclassifications	-29,818	77,794	-2,998
OTTI charges recognized in net income		9,800	47,822
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	1	279	1,660
Losses (gains) realized in net income		41,217
Total reclassifications	1	51,296	49,482
Total gain (loss) during the period	-29,817	129,090	46,484
Ending balance	7,438	37,255	-91,835
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	18,450	152,199	9,757
Unrealized holding gains (losses), net	180,005	-129,628	137,921
Total other comprehensive income (loss) before reclassifications	180,005	-129,628	137,921
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	3,373	4,008	4,530
Losses (gains) realized in net income		-8,129	-9
Total reclassifications	3,373	-4,121	4,521
Total gain (loss) during the period	183,378	-133,749	142,442
Ending balance	201,828	18,450	152,199
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	-161,617	-455,590	-457,145
Current year benefit plans gains (losses)	-347,993	260,452	-29,823
Total other comprehensive income (loss) before reclassifications	-347,993	260,452	-29,823
Amortization of prior service credit	-7,911	-7,915	-6,538
Amortization of actuarial losses	14,494	41,436	37,916
Total reclassifications	6,583	33,521	31,378
Total gain (loss) during the period	-341,410	293,973	1,555
Ending balance	-503,027	-161,617	-455,590
Beginning balance	-98,182	-276,771	-277,716
Total gain (loss) during the period	-207,407	178,589	945
Ending balance	($305,589)	($98,182)	($276,771)

Comprehensive_Income_Accumulat

Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net Consisted of Unrealized Gains (Losses) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	($64,159)	($240,264)	($356,441)
Net gain (loss) during period	-116,835	176,105	116,177
Ending balance	-180,994	-64,159	-240,264
Investment Securities With OTTI [Member] | Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	22,632	-55,790	-84,029
Net gain (loss) during period	-18,114	78,422	28,239
Ending balance	4,518	22,632	-55,790
Investment Securities All Other [Member] | Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	11,294	92,581	5,995
Net gain (loss) during period	111,389	-81,287	86,586
Ending balance	122,683	11,294	92,581
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	-98,182	-276,771	-277,716
Net gain (loss) during period	-207,407	178,589	945
Ending balance	-305,589	-98,182	-276,771
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	97	-284	-691
Net gain (loss) during period	-2,703	381	407
Ending balance	($2,606)	$97	($284)

Recovered_Sheet9

Other Income and Other Expense - Other Income and Other Expense (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other income:
Bank owned life insurance	$50,004	$56,120	$51,199
Credit-related fee income	72,454	72,271	68,596
Letter of credit fees	56,708	59,889	58,496
Gains from loan securitization transactions		63,066
Other expense:
Professional services	401,946	335,794	248,544
Amortization of capitalized servicing rights	68,410	65,354	59,555
Advertising and promotion		$56,597	$52,388

International_Activities_Addit

International Activities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
International Activities [Abstract]
Revenues from international trust-related services	$31,000,000	$26,000,000	$24,000,000
Net assets identified with international activities	232,000,000	226,000,000
Loans to foreign borrowers	213,000,000	192,000,000
Deposits at Cayman Islands office	$176,582,000	$322,746,000

Recovered_Sheet10

Derivative Financial Instruments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans	$28,000,000	$23,000,000
Aggregate fair value of derivative financial instruments in a liability position	161,000,000	194,000,000
Net liability positions with counterparties	103,000,000	107,000,000
Post collateral requirements relating to positions	90,000,000	95,000,000
Aggregate fair value of derivative financial instruments in asset position	104,000,000	183,000,000
Net asset positions with counterparties	46,000,000	95,000,000
Counterparties posted collateral relating to positions	46,000,000	93,000,000
Clearinghouse Credit Facilities [Member]
Derivative [Line Items]
Post collateral requirements relating to positions	61,000,000	14,000,000
Net fair value of derivative instruments, liability portion	35,000,000
Net fair value of derivative instruments, asset portion		5,000,000
Credit Risk Derivative [Member]
Derivative [Line Items]
Aggregate fair value of derivative financial instruments in a net liability position	22,000,000
Fair value of collateral already posted for derivative financial instruments	14,000,000
Fair value of additional collateral to be posted for derivative financial instruments	8,000,000
Interest Rate Swap Agreements [Member]
Derivative [Line Items]
Increase in net interest income due to interest rate swap agreements	45,000,000	41,000,000	36,000,000
Average notional amounts of interest rate swap agreements impacting net interest income, contract entered into for interest rate risk management purposes	1,400,000,000	1,200,000,000	900,000,000
Notional amounts of derivative contracts entered into for trading purposes	1,400,000,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading purposes	17,600,000,000	17,400,000,000
Foreign Currency and Other Option and Futures Contracts [Member]
Derivative [Line Items]
Notional amounts of derivative contracts entered into for trading purposes	$1,300,000,000	$1,400,000,000

Recovered_Sheet11

Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) (Fixed Rate Long-Term Borrowings [Member], Fair Value Hedges [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fixed Rate Long-Term Borrowings [Member] | Fair Value Hedges [Member]
Derivative [Line Items]
Notional Amount	$1,400,000,000	$1,400,000,000
Average Maturity (in years)	2 years 8 months 12 days	3 years 8 months 12 days
Weighted-Average Rate, Fixed	4.42%	4.42%
Weighted-Average Rate, Variable	1.19%	1.20%
Estimated Fair Value Gain	$73,251,000	$102,875,000

Derivative_Financial_Instrumen2

Derivative Financial Instruments - Notional Amount of Interest Rate Swap Agreements Outstanding Maturity (Detail) (Interest Rate Swap Agreements [Member], USD $)	Dec. 31, 2014
Interest Rate Swap Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
2016	$500,000,000
2017	400,000,000
2018	500,000,000
Total	$1,400,000,000

Derivative_Financial_Instrumen3

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	$338,855	$414,263
Liability derivatives, Fair value	212,059	254,189
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	264,876	304,431
Liability derivatives, Fair value	207,842	253,702
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	73,979	109,832
Liability derivatives, Fair value	4,217	487
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	73,251	102,875
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	754	6,120
Liability derivatives, Fair value	4,330	230
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	728	6,957
Liability derivatives, Fair value	4,217	487
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	17,396	7,616
Liability derivatives, Fair value	49	3,675
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	215,614	274,864
Liability derivatives, Fair value	173,513	234,455
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	31,112	15,831
Liability derivatives, Fair value	$29,950	$15,342

Derivative_Financial_Instrumen4

Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Statement of Income (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	($3,321)	$6,455	$4,034
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	3,398	9,824	8,004
Foreign Exchange and Other Option and Futures Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	-6,719	-3,369	-3,970
Interest Rate Swap Agreements [Member] | Fixed Rate Long-Term Borrowings [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives in fair value hedging relationships, Derivatives	-29,624	-40,304	-4,123
Derivatives in fair value hedging relationships, Hedged item	$28,870	$38,986	$3,724

Recovered_Sheet12

Variable Interest Entities and Asset Securitizations - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entity Disclosure [Abstract]
Residential mortgage loans securitized with Ginnie Mae	$133,000,000	$3,000,000,000
Residential mortgage loans securitized formerly held in Company's portfolio		1,300,000,000
Recognized gain		42,000,000
Gains of newly originated loans		28,000,000
Automobile loans securitized and sold	0	1,400,000,000
Recognized gain sale of securities		20,683,000
Carrying value of loans in the Securitization trusts	98,000,000	121,000,000
Combined outstanding principal amount of mortgage-backed securities issued by qualified special purpose trust held by unrelated parties	15,000,000	18,000,000
Other assets for its "investment" in the common securities recognized by the company of various trusts	34,000,000	34,000,000
Total assets of real estate partnerships in which the company invested	1,200,000,000	1,300,000,000
Maximum exposure to loss of investments in real estate partnerships	243,000,000	236,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	$56,000,000	$45,000,000

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of independent pricing sources used to value privately issued mortgage-backed securities valued with internal modeling	2
Securities issued by financial institutions and other entities backed by trust preferred securities at cost	$30	$42
Fair value of securities issued by financial institutions and other entities backed by trust preferred securities	50	63
Other-than-temporary losses			5
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	55	58	67
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	173	222	335
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	19	29
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	94	173	207
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	$79	$49	$128
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount margin over LIBOR	5.00%
Discount rates for fair value estimations	15.00%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount margin over LIBOR	10.00%
Discount rates for fair value estimations	90.00%
Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount margin over LIBOR	8.00%

Fair_Value_Measurements_Assets

Fair Value Measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	$308,175	$376,131
Investment securities	9,156,932	4,531,786
Real estate loans held for sale	742,249	468,650
Other assets	92,129	123,568
Total assets	10,299,485	5,500,135
Trading account liabilities	203,464	249,797
Other liabilities	8,596	4,392
Total liabilities	212,060	254,189
U.S. Treasury and Federal Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	161,947	37,776
Obligations of States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	8,198	10,811
Government Issued or Guaranteed [Member] | Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	8,731,123	4,165,086
Privately Issued Mortgage-Backed Securities [Member] | Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	103	1,850
Collateralized Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	50,316	63,083
Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	121,488	120,085
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	83,757	133,095
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	51,416	51,386
Investment securities	64,841	82,450
Total assets	116,257	133,836
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	64,841	82,450
Significant Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	256,759	324,745
Investment securities	9,041,672	4,384,403
Real estate loans held for sale	742,249	468,650
Other assets	74,733	115,952
Total assets	10,115,413	5,293,750
Trading account liabilities	203,464	249,797
Other liabilities	8,547	717
Total liabilities	212,011	250,514
Significant Observable Inputs (Level 2) [Member] | U.S. Treasury and Federal Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	161,947	37,776
Significant Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	8,198	10,811
Significant Observable Inputs (Level 2) [Member] | Government Issued or Guaranteed [Member] | Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	8,731,123	4,165,086
Significant Observable Inputs (Level 2) [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	121,488	120,085
Significant Observable Inputs (Level 2) [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	18,916	50,645
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	50,419	64,933
Other assets	17,396	7,616
Total assets	67,815	72,549
Other liabilities	49	3,675
Total liabilities	49	3,675
Significant Unobservable Inputs (Level 3) [Member] | Privately Issued Mortgage-Backed Securities [Member] | Mortgage-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	103	1,850
Significant Unobservable Inputs (Level 3) [Member] | Collateralized Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities	$50,316	$63,083

Fair_Value_Measurements_Change

Fair Value Measurements - Changes in Level 3 Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Assets and Other Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$3,941	$47,859	$6,923
Total gains (losses) realized/unrealized:
Included in earnings	83,417	97,845	212,281
Transfers in and/or out of Level 3	-70,011	-141,763	-171,345
Ending Balance	17,347	3,941	47,859
Changes in unrealized gains (losses) included in earnings related to assets still held at end of period	18,196	3,431	47,859
Mortgage-backed Securities, Privately Issued [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,850	1,023,886	1,151,285
Total gains (losses) realized/unrealized:
Included in earnings		-56,102	-42,467
Included in other comprehensive income	271	116,359	114,592
Sales		-978,608
Settlements	-2,018	-103,685	-199,524
Ending Balance	103	1,850	1,023,886
Changes in unrealized gains (losses) included in earnings related to assets still held at end of period			-42,467
Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	63,083	61,869	52,500
Total gains (losses) realized/unrealized:
Included in other comprehensive income	8,209	4,508	12,214
Settlements	-20,976	-3,294	-2,845
Ending Balance	$50,316	$63,083	$61,869

Fair_Value_Measurements_Quanti

Fair Value Measurements - Quantitative Information Related to Significant Unobservable Inputs (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Mortgage-backed Securities, Privately Issued [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$103	$1,850	$1,023,886	$1,151,285
Valuation technique	Two independent pricing quotes	Two independent pricing quotes
Unobservable inputs/ assumptions	-
Mortgage-backed Securities, Privately Issued [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default
Collateralized Debt Obligations [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	50,316	63,083	61,869	52,500
Valuation technique	Discounted cash flow	Discounted cash flow
Unobservable inputs/ assumptions	Probability of default Loss severity	Probability of default Loss severity
Collateralized Debt Obligations [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default	36.00%	39.00%
Loss severity	100.00%	100.00%
Collateralized Debt Obligations [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default	12.00%	17.00%
Collateralized Debt Obligations [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Probability of default	57.00%	55.00%
Other Assets and Other Liabilities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$17,347	$3,941	$47,859	$6,923
Valuation technique	Discounted cash flow	Discounted cash flow
Unobservable inputs/ assumptions	Commitment expirations	Commitment expirations
Other Assets and Other Liabilities [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commitment expirations weighted-average	17.00%	20.00%
Other Assets and Other Liabilities [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commitment expirations	0.00%	0.00%
Other Assets and Other Liabilities [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commitment expirations	96.00%	90.00%

Fair_Value_Measurements_Carryi

Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Financial assets:
Cash and cash equivalents	$1,373,357	$1,672,934	$1,986,615	$1,452,397
Interest-bearing deposits at banks	6,470,867	1,651,138
Trading account assets	308,175	376,131
Investment securities	12,993,542	8,796,497
Loans and leases:
Residential real estate loans	8,636,794	8,911,554
Consumer loans	10,969,879	10,280,527
Allowance for credit losses	-919,562	-916,676	-925,860	-908,290
Loans and leases, net	65,749,394	63,156,483
Financial liabilities:
Noninterest-bearing deposits	-26,947,880	-24,661,007
Time deposits	-3,063,973	-3,523,838
Deposits at Cayman Islands office	-176,582	-322,746
Long-term borrowings	-9,006,959	-5,108,870
Trading account liabilities	-203,464	-249,797
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,296,923	1,596,877
Trading account assets	51,416	51,386
Investment securities	64,841	82,450
Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	76,434	76,057
Interest-bearing deposits at banks	6,470,867	1,651,138
Trading account assets	256,759	324,745
Investment securities	12,750,396	8,384,106
Loans and leases:
Commercial real estate loans	307,667	67,505
Residential real estate loans	5,189,086	5,432,207
Loans and leases, net	5,496,753	5,499,712
Accrued interest receivable	227,348	222,558
Financial liabilities:
Noninterest-bearing deposits	-26,947,880	-24,661,007
Savings deposits and NOW accounts	-43,393,618	-38,611,021
Time deposits	-3,086,126	-3,542,789
Deposits at Cayman Islands office	-176,582	-322,746
Short-term borrowings	-192,676	-260,455
Long-term borrowings	-9,139,789	-5,244,902
Accrued interest payable	-63,372	-43,419
Trading account liabilities	-203,464	-249,797
Other financial instruments:
Commitments to sell real estate loans	-7,065	12,360
Interest rate swap agreements used for interest rate risk management	73,251	102,875
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Investment securities	208,719	223,938
Loans and leases:
Commercial loans and leases	19,188,574	18,457,288
Commercial real estate loans	27,180,151	25,950,690
Residential real estate loans	3,539,970	3,435,665
Consumer loans	10,909,623	10,201,087
Loans and leases, net	60,818,318	58,044,730
Other financial instruments:
Commitments to originate real estate loans for sale	17,347	3,941
Other credit-related commitments	-119,079	-118,886
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,373,357	1,672,934
Interest-bearing deposits at banks	6,470,867	1,651,138
Trading account assets	308,175	376,131
Investment securities	12,993,542	8,796,497
Loans and leases:
Commercial loans and leases	19,461,292	18,705,216
Commercial real estate loans	27,567,569	26,148,208
Residential real estate loans	8,657,301	8,928,221
Consumer loans	10,982,794	10,291,514
Allowance for credit losses	-919,562	-916,676
Loans and leases, net	65,749,394	63,156,483
Accrued interest receivable	227,348	222,558
Financial liabilities:
Noninterest-bearing deposits	-26,947,880	-24,661,007
Savings deposits and NOW accounts	-43,393,618	-38,611,021
Time deposits	-3,063,973	-3,523,838
Deposits at Cayman Islands office	-176,582	-322,746
Short-term borrowings	-192,676	-260,455
Long-term borrowings	-9,006,959	-5,108,870
Accrued interest payable	-63,372	-43,419
Trading account liabilities	-203,464	-249,797
Other financial instruments:
Commitments to originate real estate loans for sale	17,347	3,941
Commitments to sell real estate loans	-7,065	12,360
Other credit-related commitments	-119,079	-118,886
Interest rate swap agreements used for interest rate risk management	73,251	102,875
Estimate Fair Value [Member]
Financial assets:
Cash and cash equivalents	1,373,357	1,672,934
Interest-bearing deposits at banks	6,470,867	1,651,138
Trading account assets	308,175	376,131
Investment securities	13,023,956	8,690,494
Loans and leases:
Commercial loans and leases	19,188,574	18,457,288
Commercial real estate loans	27,487,818	26,018,195
Residential real estate loans	8,729,056	8,867,872
Consumer loans	10,909,623	10,201,087
Loans and leases, net	66,315,071	63,544,442
Accrued interest receivable	227,348	222,558
Financial liabilities:
Noninterest-bearing deposits	-26,947,880	-24,661,007
Savings deposits and NOW accounts	-43,393,618	-38,611,021
Time deposits	-3,086,126	-3,542,789
Deposits at Cayman Islands office	-176,582	-322,746
Short-term borrowings	-192,676	-260,455
Long-term borrowings	-9,139,789	-5,244,902
Accrued interest payable	-63,372	-43,419
Trading account liabilities	-203,464	-249,797
Other financial instruments:
Commitments to originate real estate loans for sale	17,347	3,941
Commitments to sell real estate loans	-7,065	12,360
Other credit-related commitments	-119,079	-118,886
Interest rate swap agreements used for interest rate risk management	$73,251	$102,875

Recovered_Sheet13

Commitments and Contingencies - Company's Significant Commitments (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Commitments to extend credit
Home equity lines of credit	$6,194,516	$6,218,823
Commercial real estate loans to be sold	212,257	62,386
Other commercial real estate and construction	4,834,699	3,919,545
Residential real estate loans to be sold	432,352	469,869
Other residential real estate	524,399	384,617
Commercial and other	11,080,856	10,419,545
Standby letters of credit	3,706,888	3,600,528
Commercial letters of credit	46,965	53,284
Financial guarantees, indemnification contracts and other	2,490,050	2,457,633
Commitments to sell real estate loans	$1,237,294	$854,656

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	$2,400,000,000	$2,300,000,000
Period of noncancelable operating lease in years	24 years
Range of reasonably possible losses, minimum	0
Range of reasonably possible losses, maximum	$40,000,000

Commitments_and_Contingencies_2

Commitments and Contingencies - Minimum Lease Payments Under Noncancellable Operating Leases (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
2015	$87,063
2016	83,315
2017	70,108
2018	56,024
2019	45,079
Later years	113,390
Total	$454,979

Segment_Information_Informatio

Segment Information - Information about Company's Segments (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net interest income	$2,676,446,000	$2,673,229,000	$2,598,516,000
Noninterest income	1,779,273,000	1,865,205,000	1,667,270,000
Total income	4,455,719,000	4,538,434,000	4,265,786,000
Provision for credit losses	124,000,000	185,000,000	204,000,000
Amortization of core deposit and other intangible assets	33,824,000	46,912,000	60,631,000
Depreciation and other amortization	164,906,000	156,823,000	143,930,000
Other noninterest expense	2,544,127,000	2,432,150,000	2,304,699,000
Income (loss) before taxes	1,588,862,000	1,717,549,000	1,552,526,000
Income tax expense (benefit)	522,616,000	579,069,000	523,028,000
Net income (loss)	1,066,246,000	1,138,480,000	1,029,498,000
Average total assets	92,143,000,000	83,662,000,000	79,983,000,000
Capital expenditures	73,000,000	130,000,000	92,000,000
All Other [Member]
Segment Reporting Information [Line Items]
Net interest income	168,836,000	43,904,000	-80,894,000
Noninterest income	592,270,000	670,889,000	501,390,000
Total income	761,106,000	714,793,000	420,496,000
Provision for credit losses	-12,954,000	-3,094,000	4,917,000
Amortization of core deposit and other intangible assets	33,824,000	46,912,000	60,631,000
Depreciation and other amortization	61,848,000	57,120,000	50,536,000
Other noninterest expense	844,972,000	690,150,000	693,046,000
Income (loss) before taxes	-166,584,000	-76,295,000	-388,634,000
Income tax expense (benefit)	-122,733,000	-78,841,000	-207,887,000
Net income (loss)	-43,851,000	2,546,000	-180,747,000
Average total assets	12,277,000,000	9,442,000,000	7,952,000,000
Capital expenditures	57,000,000	89,000,000	76,000,000
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	90,123,000	98,496,000	78,058,000
Noninterest income	331,391,000	325,474,000	402,211,000
Total income	421,514,000	423,970,000	480,269,000
Provision for credit losses	-2,357,000	-11,711,000	17,169,000
Depreciation and other amortization	47,108,000	48,716,000	46,902,000
Other noninterest expense	222,396,000	225,794,000	195,604,000
Income (loss) before taxes	154,367,000	161,171,000	220,594,000
Income tax expense (benefit)	59,361,000	61,779,000	85,671,000
Net income (loss)	95,006,000	99,392,000	134,923,000
Average total assets	3,333,000,000	2,858,000,000	2,451,000,000
Capital expenditures			1,000,000
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	741,109,000	810,134,000	902,906,000
Noninterest income	335,501,000	373,362,000	349,571,000
Total income	1,076,610,000	1,183,496,000	1,252,477,000
Provision for credit losses	77,158,000	72,502,000	95,345,000
Depreciation and other amortization	37,788,000	34,599,000	32,734,000
Other noninterest expense	759,569,000	768,644,000	751,916,000
Income (loss) before taxes	202,095,000	307,751,000	372,482,000
Income tax expense (benefit)	82,179,000	125,350,000	151,616,000
Net income (loss)	119,916,000	182,401,000	220,866,000
Average total assets	10,449,000,000	10,997,000,000	11,705,000,000
Capital expenditures	14,000,000	40,000,000	15,000,000
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	317,356,000	325,521,000	347,067,000
Noninterest income	105,370,000	102,945,000	103,283,000
Total income	422,726,000	428,466,000	450,350,000
Provision for credit losses	18,885,000	26,450,000	22,245,000
Depreciation and other amortization	405,000	198,000	122,000
Other noninterest expense	200,802,000	214,043,000	179,428,000
Income (loss) before taxes	202,634,000	187,775,000	248,555,000
Income tax expense (benefit)	82,825,000	76,735,000	101,484,000
Net income (loss)	119,809,000	111,040,000	147,071,000
Average total assets	5,281,000,000	5,080,000,000	4,909,000,000
Capital expenditures	2,000,000	1,000,000
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	745,218,000	758,231,000	753,678,000
Noninterest income	259,832,000	263,766,000	253,808,000
Total income	1,005,050,000	1,021,997,000	1,007,486,000
Provision for credit losses	33,197,000	76,818,000	15,781,000
Depreciation and other amortization	588,000	564,000	567,000
Other noninterest expense	274,697,000	288,842,000	262,820,000
Income (loss) before taxes	696,568,000	655,773,000	728,318,000
Income tax expense (benefit)	285,429,000	264,433,000	296,894,000
Net income (loss)	411,139,000	391,340,000	431,424,000
Average total assets	22,892,000,000	21,655,000,000	19,946,000,000
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	539,600,000	570,786,000	531,398,000
Noninterest income	127,445,000	130,895,000	133,120,000
Total income	667,045,000	701,681,000	664,518,000
Provision for credit losses	-6,476,000	7,365,000	4,238,000
Depreciation and other amortization	16,278,000	14,296,000	11,004,000
Other noninterest expense	207,757,000	214,246,000	190,879,000
Income (loss) before taxes	449,486,000	465,774,000	458,397,000
Income tax expense (benefit)	133,357,000	143,981,000	149,321,000
Net income (loss)	316,129,000	321,793,000	309,076,000
Average total assets	17,113,000,000	17,150,000,000	16,437,000,000
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	74,204,000	66,157,000	66,303,000
Noninterest income	27,464,000	-2,126,000	-76,113,000
Total income	101,668,000	64,031,000	-9,810,000
Provision for credit losses	16,547,000	16,670,000	44,305,000
Depreciation and other amortization	891,000	1,330,000	2,065,000
Other noninterest expense	33,934,000	30,431,000	31,006,000
Income (loss) before taxes	50,296,000	15,600,000	-87,186,000
Income tax expense (benefit)	2,198,000	-14,368,000	-54,071,000
Net income (loss)	48,098,000	29,968,000	-33,115,000
Average total assets	$20,798,000,000	$16,480,000,000	$16,583,000,000

Segment_Information_Informatio1

Segment Information - Information about Company's Segments (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting [Abstract]
Taxable-equivalent adjustment	$23,642,000	$24,971,000	$26,391,000

Segment_Information_Intersegme

Segment Information - Intersegment Activity Eliminated in Arriving at Consolidated Totals was Included in "All Other" Category (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	($4,455,719)	($4,538,434)	($4,265,786)
Income taxes (benefit)	-522,616	-579,069	-523,028
Net income	-1,066,246	-1,138,480	-1,029,498
Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Revenues	-49,800	-50,128	-71,452
Expenses	-12,014	-16,235	-17,313
Income taxes (benefit)	-15,375	-13,791	-22,029
Net income	($22,411)	($20,102)	($32,110)

Regulatory_Matters_Additional_

Regulatory Matters - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Funds available for payment of dividends to M&T from banking subsidiaries	$1,500,000,000
Required subsidiary noninterest-earning reserves against certain deposit liabilities	555,575,000	595,593,000
Minimum "Tier 1 capital" ratio required for capital adequacy	4.00%
Minimum "Total capital" ratio required for capital adequacy	8.00%
Minimum "Tier 1" capital" ratio to be considered well capitalized	6.00%
Minimum "Total capital" ratio to be considered well capitalized	10.00%
Minimum "Leverage" ratio to be considered well capitalized	5.00%
Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Consolidated assets required per Federal Reserve Board to submit annual capital plans	$50,000,000,000

Regulatory_Matters_Capital_Rat

Regulatory Matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
M&T (Consolidated) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$9,644,765	$8,792,035
Ratio	12.47%	12.00%
Minimum required amount	3,093,874	2,930,925
Amount	11,767,308	11,045,589
Ratio	15.21%	15.07%
Minimum required amount	6,187,747	5,861,849
Amount	9,644,765	8,792,035
Ratio	10.17%	10.78%
Minimum required amount	3,793,836	2,446,476
M&T Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	8,043,185	7,341,506
Ratio	10.46%	10.08%
Minimum required amount	3,077,101	2,914,246
Amount	10,048,277	9,445,770
Ratio	13.06%	12.96%
Minimum required amount	6,154,201	5,828,491
Amount	8,043,185	7,341,506
Ratio	8.56%	9.09%
Minimum required amount	3,760,364	2,422,096
Wilmington Trust, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	435,558	420,330
Ratio	57.22%	73.79%
Minimum required amount	30,447	22,786
Amount	439,867	424,975
Ratio	57.79%	74.60%
Minimum required amount	60,893	45,573
Amount	435,558	420,330
Ratio	9.98%	19.80%
Minimum required amount	$174,613	$63,678

Relationship_with_Bayview_Lend1

Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	$4,800,000,000	$5,500,000,000
Revenues from servicing	26,000,000	31,000,000	35,000,000
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	47,000,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Revenues from servicing	115,000,000	33,000,000	10,000,000
Outstanding principal balances of residential mortgage loans from Bayview Financial	41,300,000,000	45,600,000,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	$202,000,000	$220,000,000

Recovered_Sheet14

Parent Company Financial Statements - Condensed Balance Sheet (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Investments in consolidated subsidiaries
Total assets	$96,685,535	$85,162,391
Liabilities
Long-term borrowings	9,006,959	5,108,870
Total liabilities	84,349,639	73,856,859
Shareholders' equity	12,335,896	11,305,532	10,202,593	9,271,209
Total liabilities and shareholders' equity	96,685,535	85,162,391
Parent Company [Member]
Assets
Cash in subsidiary bank	11,306	10,729
Due from consolidated bank subsidiaries
Money-market savings	1,096,533	968,274
Current income tax receivable		1,914
Other	12	1,894
Total due from consolidated bank subsidiaries	1,096,545	972,082
Investments in consolidated subsidiaries
Banks and bank holding company	11,945,516	11,364,657
Other	16,217	16,212
Investments in unconsolidated subsidiaries (note 19)	33,578	33,751
Investment in Bayview Lending Group LLC	46,716	73,883
Other assets	81,034	80,098
Total assets	13,230,912	12,551,412
Liabilities
Accrued expenses and other liabilities	59,950	62,817
Long-term borrowings	835,066	1,183,063
Total liabilities	895,016	1,245,880
Shareholders' equity	12,335,896	11,305,532
Total liabilities and shareholders' equity	$13,230,912	$12,551,412

Recovered_Sheet15

Parent Company Financial Statements - Condensed Statement of Income (Detail) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income
Equity in earnings of Bayview Lending Group LLC	($16,672)	($16,126)	($21,511)
Expense
Interest on long-term borrowings	217,247	199,983	225,297
Other expense	2,742,857	2,635,885	2,509,260
Income tax credits	-522,616	-579,069	-523,028
Equity in undistributed income of subsidiaries
Net income	1,066,246	1,138,480	1,029,498
Net income per common share
Basic	$7.47	$8.26	$7.57
Diluted	$7.42	$8.20	$7.54
Parent Company [Member]
Income
Dividends from consolidated bank subsidiaries	480,000	700,000	700,000
Equity in earnings of Bayview Lending Group LLC	-16,672	-16,126	-21,511
Other income	7,755	9,992	8,755
Total income	471,083	693,866	687,244
Expense
Interest on long-term borrowings	47,700	73,115	82,286
Other expense	15,107	15,994	19,226
Total expense	62,807	89,109	101,512
Income before income taxes and equity in undistributed income of subsidiaries	408,276	604,757	585,732
Income tax credits	27,284	35,986	43,149
Income before equity in undistributed income of subsidiaries	435,560	640,743	628,881
Equity in undistributed income of subsidiaries
Net income of subsidiaries	1,110,686	1,197,737	1,100,617
Less: dividends received	-480,000	-700,000	-700,000
Equity in undistributed income of subsidiaries	630,686	497,737	400,617
Net income	$1,066,246	$1,138,480	$1,029,498
Net income per common share
Basic	$7.47	$8.26	$7.57
Diluted	$7.42	$8.20	$7.54

Parent_Company_Financial_State2

Parent Company Financial Statements - Condensed Statement of Cash Flows (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities
Net income	$1,066,246	$1,138,480	$1,029,498
Adjustments to reconcile net income to net cash provided by operating activities
Provision for deferred income taxes	92,848	139,785	131,858
Net cash provided by operating activities	1,099,041	932,324	499,981
Cash flows from investing activities
Other, net	19,531	95,706	32,458
Net cash provided (used) by investing activities	-11,710,371	-2,203,578	-4,060,858
Cash flows from financing activities
Payments on long-term borrowings	-426,275	-261,212	-2,080,167
Dividends paid - common	-371,199	-365,349	-357,717
Dividends paid - preferred	-70,234	-53,450	-53,450
Other, net	88,565	137,967	63,616
Net cash provided by financing activities	10,311,753	957,573	4,095,095
Net increase in cash and cash equivalents	-299,577	-313,681	534,218
Cash and cash equivalents at beginning of year	1,672,934	1,986,615	1,452,397
Cash and cash equivalents at end of year	1,373,357	1,672,934	1,986,615
Supplemental disclosure of cash flow information
Interest paid during the year	257,553	301,734	371,887
Income taxes received during the year	411,912	389,008	405,598
Parent Company [Member]
Cash flows from operating activities
Net income	1,066,246	1,138,480	1,029,498
Adjustments to reconcile net income to net cash provided by operating activities
Equity in undistributed income of subsidiaries	-630,686	-497,737	-400,617
Provision for deferred income taxes	-6,522	1,535	1,724
Net change in accrued income and expense	23,419	31,979	6,798
Net cash provided by operating activities	452,457	674,257	637,403
Cash flows from investing activities
Proceeds from sales of investment securities			411
Investment in subsidiary		-140,000
Other, net	10,721	3,295	324
Net cash provided (used) by investing activities	10,721	-136,705	735
Cash flows from financing activities
Payments on long-term borrowings	-350,010		-300,000
Dividends paid - common	-371,199	-365,349	-357,717
Dividends paid - preferred	-70,234	-53,450	-53,450
Proceeds from issuance of preferred stock	346,500
Other, net	110,601	140,799	143,352
Net cash provided by financing activities	-334,342	-278,000	-567,815
Net increase in cash and cash equivalents	128,836	259,552	70,323
Cash and cash equivalents at beginning of year	979,003	719,451	649,128
Cash and cash equivalents at end of year	1,107,839	979,003	719,451
Supplemental disclosure of cash flow information
Interest received during the year	2,094	2,224	1,970
Interest paid during the year	47,003	71,090	80,090
Income taxes received during the year	$24,588	$45,237	$21,878