Borrowings - Long-term Borrowings (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Borrowings [Line Items]
Variable rates		$ 1,000,000
Fixed rates	30,066	398,407
Agreements to repurchase securities	1,400,000	1,400,000
Other	40,792	44,405
Long-term borrowings	4,607,758	6,686,226
Senior notes of M&T - 5.375% due 2012 [Member]
Schedule Of Borrowings [Line Items]
Senior notes		299,991
4.875% due 2013 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	251,298	255,839
8.5% due 2018 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	230,255	237,194
3.85% due 2013, variable rate commenced in 2008 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes		400,000
6.625% due 2017 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	455,439	452,655
9.5% due 2018 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	50,000	50,000
5.585% due 2020, variable rate commencing 2015 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	385,669	378,917
5.629% due 2021, variable rate commencing 2016 [Member]
Schedule Of Borrowings [Line Items]
Subordinated notes	583,097	589,516
M&T Capital Trust I - 8.234%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	154,640	154,640
M&T Capital Trust II - 8.277%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	103,093	103,093
M&T Capital Trust III - 9.25%, due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	66,434	66,759
BSB Capital Trust I - 8.125%, due 2028 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	15,566	15,542
Provident Trust I - 8.29%, due 2028 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	24,746	24,483
Southern Financial Statutory Trust I - 10.60%, due 2030 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	6,496	6,474
M&T Capital Trust IV - 8.50%, due 2068 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	350,010	350,010
First Maryland Capital I - due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	144,102	143,564
First Maryland Capital II - due 2027 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	145,301	144,638
Allfirst Asset Trust - due 2029 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	95,913	95,768
BSB Capital Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	15,464	15,464
Provident Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	51,694	51,244
Southern Financial Capital Trust III - due 2033 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures associated with preferred capital securities	$ 7,683	$ 7,623