Borrowings (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Advances from FHLB:
Variable rates	$ 1,000,000	$ 2,525,268
Fixed rates	398,407	347,161
Agreements to repurchase securities	1,400,000	1,625,001
Junior subordinated debentures of M&T associated with preferred capital securities:
Other Long-term Debt	44,405	48,384
Long-term borrowings	6,686,226	7,840,151
Senior notes of M&T - 5.375% due 2012 [Member]
Long-term borrowings
Senior Notes	299,991	299,971
3.85% due 2013, variable rate commenced in 2008 [Member]
Subordinated notes of M&T Bank:
Subordinated Debt	400,000	400,000
4.875% due 2013 [Member]
Subordinated notes of M&T Bank:
Subordinated Debt	255,839
6.625% due 2017 [Member]
Subordinated notes of M&T Bank:
Subordinated Debt	452,655	425,969
9.5% due 2018 [Member]
Subordinated notes of M&T Bank:
Subordinated Debt	50,000	50,000
8.5% due 2018 [Member]
Subordinated notes of M&T Bank:
Subordinated Debt	237,194
5.585% due 2020, variable rate commencing 2015 [Member]
Subordinated notes of M&T Bank:
Subordinated Debt	378,917	372,668
5.629% due 2021, variable rate commencing 2016 [Member]
Subordinated notes of M&T Bank:
Subordinated Debt	589,516	568,196
M&T Capital Trust I - 8.234%, due 2027 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	154,640	154,640
M&T Capital Trust II - 8.277%, due 2027 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	103,093	103,093
M&T Capital Trust III - 9.25%, due 2027 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	66,759	67,084
BSB Capital Trust I - 8.125%, due 2028 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	15,542	15,519
Provident Trust I - 8.29%, due 2028 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	24,483	24,256
Southern Financial Statutory Trust I - 10.60%, due 2030 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	6,474	6,455
M&T Capital Trust IV - 8.50%, due 2068 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	350,010	350,010
First Maryland Capital I Variable Rates Due 2027 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	143,564	143,025
First Maryland Capital II - due 2027 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	144,638	143,975
Allfirst Asset Trust - due 2029 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	95,768	95,623
BSB Capital Trust III - due 2033 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	15,464	15,464
Provident Trust III - due 2033 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	51,244	50,823
Southern Financial Capital Trust III - due 2033 [Member]
Junior subordinated debentures of M&T associated with preferred capital securities:
Junior subordinated debentures associated with preferred capital securities	$ 7,623	$ 7,566