Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended					1 Months Ended			1 Months Ended		12 Months Ended		3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Aug. 27, 2012	Aug. 27, 2012 Common Stock [Member]	May 31, 2012 Minimum [Member]	May 31, 2011 Maximum [Member]	Aug. 27, 2012 Cash [Member]	May 31, 2011 Wilmington Trust Corporation Acquisition [Member]	May 16, 2011 Wilmington Trust Corporation Acquisition [Member] Office	Dec. 31, 2011 Wilmington Trust Corporation Acquisition [Member]	Dec. 31, 2010 Wilmington Trust Corporation Acquisition [Member]	Dec. 31, 2010 K Bank Acquisition [Member]	Nov. 05, 2010 K Bank Acquisition [Member]	Dec. 31, 2012 Hudson City [Member]
Business Acquisition [Line Items]
Total consideration in shares				$ 0.08403
Percentage of total consideration					60.00%			40.00%
Total consideration to be paid	$ 4,200,000,000
Assets															40,600,000,000
Loans															27,200,000,000
Investment securities	6,074,361,000	7,673,154,000													11,500,000,000
Liabilities	72,806,210,000	68,653,078,000													35,900,000,000
Deposits	65,611,253,000	59,394,649,000													23,500,000,000
Long-term borrowing	4,607,758,000	6,686,226,000													12,000,000,000
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										10,845,042,000				556,000,000
Loans and leases										6,410,430,000				154,000,000
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										10,044,555,000				528,000,000
Deposits										8,864,161,000				491,000,000
Value added in shareholders equity due to acquisition										406,000,000
Preferred stock redeemed in connection with Willington Trust acquisition										330,000,000
Core deposit and other intangibles										112,000,000
Intangible Assets Amortization						5 years	7 years
Realized non-taxable gain									65,000,000
Provision for credit losses	204,000,000	270,000,000	368,000,000								42,000,000	700,000,000
Other- than-temporary impairment											5,000,000	38,000,000
Merger related expenses associated with acquisition of Wilmington Trust		84,000,000
Cash and due from banks										178,940,000				186,000,000
After-tax gain on M&T & K Bank transaction													17,000,000
Pre-tax gain on acquisitions		$ 64,930,000								$ 64,930,000			$ 28,000,000