Acquisitions (Details Textual) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended				3 Months Ended		1 Months Ended	9 Months Ended		4 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 K Bank and Wilmington Trust Corporation Acquisition [Member]	Sep. 30, 2011 K Bank and Wilmington Trust Corporation Acquisition [Member]	Sep. 30, 2011 Wilmington Trust Corporation Acquisition [Member]	Sep. 30, 2010 Wilmington Trust Corporation Acquisition [Member]	May 16, 2011 Wilmington Trust Corporation Acquisition [Member] Office	Dec. 31, 2010 K Bank Acquisition [Member]	Nov. 05, 2010 K Bank Acquisition [Member]	May 31, 2011 Wilmington Trust Corporation [Member]	Sep. 30, 2011 Wilmington Trust Corporation [Member]	May 16, 2011 Wilmington Trust Corporation [Member]	Sep. 30, 2011 Minimum [Member] Year	Sep. 30, 2011 Maximum [Member] Year
Acquisitions (Textual) [Abstract]
Number of banking offices operated									55
Shares of M&T common stock exchanged for each share of Wilmington Trust common stock									0.051372
Common stock issued for acquisition							4,694,486
Common shares issued for acquisition fair value									$ 406,000,000
Assets acquired total									10,800,000,000		556,000,000			10,845,042,000
Loans and leases									6,400,000,000		154,000,000			6,410,430,000
Commercial real estate loans									3,200,000,000
Commercial loans and leases									1,400,000,000
Consumer loans									1,100,000,000
Residential real estate loans									680,000,000
Liabilities									10,000,000,000		528,000,000			10,044,555,000
Deposits									8,900,000,000		491,000,000			8,864,161,000
Value added in shareholders equity due to acquisition									406,000,000
Preferred stock redeemed in connection with Willington Trust acquisition									330,000,000
Intangible Assets Amortization Period															5	7
Core deposit and other intangibles									176,000,000
Common shares issued for acquisition													4,694,486
Provision for credit losses	58,000,000	93,000,000	196,000,000	283,000,000			42,000,000	564,000,000
Other- than-temporary impairment							5,000,000	30,000,000
Cash and due from banks											186,000,000			178,940,000
After-tax gain on K Bank transaction										17,000,000
Pre-tax gain on acquisitions										28,000,000		64,930,000
Contractually required principal and interest at acquisition of impaired loans									1,419,672,000
Contractual cash flows expected to be collected of impaired loans									747,265,000
Fair value of loans acquired of impaired loans									707,907,000
Additional Acquisitions (Textual) [Abstract]
Realized non taxable gain			65,000,000
Merger related expenses associated with acquisition of Wilmington Trust		0	67,000,000	0	26,003,000	67,294,000
Unpaid portion of merger-related expenses	$ 17,000,000		$ 17,000,000