Borrowings - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Schedule Of Borrowings [Line Items]
Junior subordinated debentures face value	$ 1,200,000,000
Junior Subordinated Debentures Maturity Date	Jan. 31, 2068
Debt Maturity, Start Year	Jan. 01, 2027
Debt Maturity, End Year	Dec. 31, 2068
Agreements to repurchase securities	1,400,000,000	1,400,000,000
Junior Subordinated Debenture due January 31, 2068 [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures	350,000,000
Unsecured senior and subordinated notes [Member] | M&T Bank [Member]
Schedule Of Borrowings [Line Items]
Maximum unsecured senior and subordinate notes available for offering	5,000,000,000
Maturity of unsecured senior and subordinate notes from the date of issue	270 days or more
Floating rate senior notes due March 2016 [Member] | M&T Bank [Member]
Schedule Of Borrowings [Line Items]
Senior notes	300,000,000
Term of senior notes, year	3 years
Maturity period of senior notes	2016-03
Fixed rate senior notes due March 2018 [Member] | M&T Bank [Member]
Schedule Of Borrowings [Line Items]
Senior notes	$ 500,000,000
Term of senior notes, year	5 years
Interest rate of senior notes	1.45%
Maturity period of senior notes	2018-03