Acquisitions (Details 3) (USD $)	3 Months Ended		6 Months Ended				3 Months Ended	6 Months Ended		12 Months Ended		3 Months Ended		1 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Nov. 05, 2010	Jun. 30, 2011 K Bank And Wilmington Trust Corporation Acquisition [Member]	Jun. 30, 2011 K Bank And Wilmington Trust Corporation Acquisition [Member]	Jun. 30, 2011 Wilmington Trust Corporation Acquisition [Member]	Dec. 31, 2010 Wilmington Trust Corporation Acquisition [Member]	May 16, 2011 Wilmington Trust Corporation Acquisition [Member]	Dec. 31, 2010 K Bank Acquisition [Member]	Nov. 05, 2010 K Bank Acquisition [Member]	Jun. 30, 2011 Minimum [Member]	Jun. 30, 2011 Maximum [Member]
Summary of merger-related expenses
Salaries and employee benefits	$ 300,178,000	$ 245,861,000	$ 566,268,000	$ 509,907,000			$ 15,305,000	$ 15,312,000
Equipment and net occupancy	59,670,000	55,431,000	116,333,000	110,832,000			25,000	104,000
Printing, postage and supplies	9,723,000	8,549,000	18,925,000	17,592,000			318,000	465,000
Other costs of operations	165,975,000	129,786,000	302,183,000	252,835,000			21,348,000	25,410,000
Total merger-related expenses		0	41,000,000	0			36,996,000	41,291,000
Acquisitions (Textuals) [Abstract]
Assets acquired						556,000,000
Common stock issued for acquisition									4,694,486
Assets acquired total											10,800,000,000
Loans and leases											6,400,000,000		154,000,000
Cash and due from banks													186,000,000
Liabilities											10,000,000,000		528,000,000
Deposits											8,900,000,000		491,000,000
Commercial real estate loans											3,200,000,000
Commercial loans and leases											1,400,000,000
Shares of M&T common stock exchanged for each share of Wilmington Trust common stock											0.051372
Consumer loans											1,100,000,000
Residential real estate loans											680,000,000
Core deposit and other intangibles											176,000,000
After-tax gain on K Bank transaction												17,000,000
Pre-tax gain on K Bank transaction												28,000,000
Provision for credit losses	63,000,000	85,000,000	138,000,000	190,000,000					42,000,000	283,000,000
Other- than-temporary impairment									5,000,000	26,000,000
Value added in shareholders equity due to acquisition											406,000,000
Investment securities	6,492,265,000		6,492,265,000		7,150,540,000
Number of banking offices operated											55
Common shares issued for acquisition fair value											406,000,000
Preferred stock to be assumed as part of Willington Trust acquisition											330,000,000
Intangible Assets Amortization Period														5	7
Additional Acquisitions (Textuals) [Abstract]
Merger related expenses associated with acquisition of Wilmington Trust		0	41,000,000	0			36,996,000	41,291,000
Common shares issued for acquisition			4,694,486
Restricted shares issued for acquisition	3,216		3,216
Realized non taxable gain			65,000,000
Net gain resulting from acquisition												28,000,000
Unpaid portion of merger-related expenses	24,000,000		24,000,000
Contractually required principal and interest at acquisition of impaired loans	1,419,672,000		1,419,672,000
Contractual cash flows not expected to be collected of impaired loans	747,265,000		747,265,000
Fair value of loans acquired of impaired loans	$ 707,907,000		$ 707,907,000