Borrowings - Additional Information (Detail) (USD $)	12 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Junior Subordinated Debenture due January 31, 2068 [Member]	Dec. 31, 2012 M&T (Consolidated) [Member]	Dec. 31, 2012 M&T Bank [Member]	Dec. 31, 2012 Federal Reserve Bank of New York [Member]	Dec. 31, 2011 FHLB Atlanta [Member]	Dec. 31, 2012 Long-term variable rate advances from FHLB [Member]	Dec. 31, 2011 Long-term variable rate advances from FHLB [Member]	Dec. 31, 2012 Long-term fixed rate advances from the FHLB [Member]	Dec. 31, 2011 Long-term fixed rate advances from the FHLB [Member]	Jul. 02, 2012 Subordinated capital notes [Member]
Schedule Of Borrowings [Line Items]
Federal funds purchased and short-term repurchase agreements outstanding							$ 50,000,000
Maximum amount of borrower using revolving credit agreement				30,000,000
Borrowing facilities available with FHLB's amount					9,800,000,000
Line of credit facility						11,700,000,000
Revolving credit maturity date				Nov. 25, 2013
Variable contractual interest rate of long-term debt lower limit								0.00%	0.26%	3.48%	0.79%
Variable contractual interest rate of long-term debt upper limit								0.00%	0.36%	7.32%	7.32%
Weighted-average contractual variable interest rate								0.00%	0.29%	4.64%	3.52%
Advances from the FHLB maturity date								2035
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
Subordinated capital notes redeemed												400,000,000
Subordinated capital notes maturity period	2013
Minimum variable interest rate of Junior Subordinated Debentures	1.16%	1.28%
Maximum variable interest rate of Junior Subordinated Debentures	3.69%	3.92%
Weighted-average variable rates payable on Junior Subordinated Debentures	1.75%	1.87%
Junior subordinated debentures			$ 350,000,000
Junior Subordinated Debentures Maturity Date	Jan. 31, 2068
Debt Maturity, Start Year	Jan. 01, 2027
Debt Maturity, End Year	Dec. 31, 2068