Borrowings - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended		3 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Junior Subordinated Debenture due January 31, 2068 [Member]	Mar. 31, 2013 Unsecured senior and subordinated notes [Member] M&T Bank [Member]	Mar. 31, 2013 Floating rate senior notes due March 2016 [Member] M&T Bank [Member]	Mar. 31, 2013 Fixed rate senior notes due March 2018 [Member] M&T Bank [Member]
Schedule Of Borrowings [Line Items]
Junior subordinated debentures	$ 1,200,000,000		$ 350,000,000
Percentage of outstanding securities in Tier 1 capital in 2015	25.00%
Percentage outstanding securities included in tier one capital beginning in 2016	0.00%
Junior Subordinated Debentures Maturity Date	Jan. 31, 2068
Debt Maturity, Start Year	Jan. 01, 2027
Debt Maturity, End Year	Dec. 31, 2068
Maximum unsecured senior and subordinate notes available for offering				5,000,000,000
Senior notes					300,000,000	500,000,000
Term of senior notes, year					3 years	5 years
Interest rate of senior notes						1.45%
Maturity period of senior notes					2016-03	2018-03
Agreements to repurchase securities	1,400,000,000	1,400,000,000
Collateral posted	$ 1,600,000,000	$ 1,600,000,000