Borrowings - Long-term Borrowings (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Borrowings [Line Items]
Debt Maturity, Start Date	Jan. 01, 2027
Debt Maturity, End Date	Dec. 31, 2068
Senior notes of M&T - 5.375% due 2012 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	5.375%	5.375%
Debt maturity date	2012	2012
4.875% due 2013 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	4.875%	4.875%
Debt maturity date	2013	2013
8.5% due 2018 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.50%	8.50%
Debt maturity date	2018	2018
3.85% due 2013, variable rate commenced in 2008 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	3.85%	3.85%
Debt Maturity, Start Date	Jan. 01, 2008	Jan. 01, 2008
Debt Maturity, End Date	Dec. 31, 2013	Dec. 31, 2013
6.625% due 2017 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	6.625%	6.625%
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	5.585%	5.585%
Debt Maturity, Start Date	Jan. 01, 2015	Jan. 01, 2015
Debt Maturity, End Date	Dec. 31, 2020	Dec. 31, 2020
5.629% due 2021, variable rate commencing 2016 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	5.629%	5.629%
Debt Maturity, Start Date	Jan. 01, 2016	Jan. 01, 2016
Debt Maturity, End Date	Dec. 31, 2021	Dec. 31, 2021
M&T Capital Trust I - 8.234%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Interest rate of debt instrument	8.234%	8.234%
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	8.277%	8.277%
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	8.125%	8.125%
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