Stockholders' equity (Details) (USD $)	3 Months Ended	9 Months Ended												1 Months Ended		9 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2010 Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Sep. 30, 2011 Series B Mandatory Convertible Non-cumulative Preferred Stock [Member]	Dec. 31, 2010 Series B Mandatory Convertible Non-cumulative Preferred Stock [Member]	Sep. 30, 2011 Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2010 Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Sep. 30, 2011 Series D Fixed Rate Non Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2010 Series D Fixed Rate Non Cumulative Perpetual Preferred Stock [Member]	Sep. 30, 2011 Ten Year Warrant Series A Preferred [Member]	Sep. 30, 2011 Ten Year Warrant Series C Preferred [Member]	May 31, 2011 Series A [Member]	Sep. 30, 2011 Series A [Member]	Sep. 30, 2011 Series B [Member]	Sep. 30, 2011 Series C [Member]	Sep. 30, 2011 Series D [Member]	Sep. 30, 2011 Preferred series A and C first five years [Member]	Sep. 30, 2011 Preferred series A and C after five years [Member]
Issued and outstanding preferred stock
Preferred stock, shares issued	381,500	381,500	778,000	230,000	600,000		26,500	151,500	151,500	50,000
Preferred stock, shares outstanding	50,000	50,000		230,000	600,000		26,500	151,500	151,500	50,000
Carrying value	$ 862,717,000	$ 862,717,000	$ 740,657,000	$ 223,645,000	$ 578,630,000	$ 0	$ 26,500,000	$ 139,072,000	$ 135,527,000	$ 500,000,000	$ 0
Shareholders Equity (Textual) [Abstract]
Preferred stock, par value	$ 1.00	$ 1.00	$ 1.00
Liquidation preference	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000		$ 1,000	$ 1,000	$ 1,000	$ 10,000
Preferred stock, shares authorized	1,000,000	1,000,000	1,000,000	230,000	600,000		26,500	151,500	151,500	50,000
Ten-year warrant to purchase common stock												1,218,522	407,542
Exercise price of each class of warrants or rights outstanding															$ 73.86		$ 55.76
Preferred stock dividend rate																10.00%		6.875%	5.00%	9.00%
Number of shares of M&T common stock resulting from conversion of Series B Preferred																433,144
Preferred stock, shares redeemed														370,000
Accelerated amortization of preferred stock discount as per redemption														$ 11,200,000
Limitation by U.S. Treasury on maximum amount of dividend to be paid per common stock quarterly	0.70 per share
Redemption days of shares by Company		90 days