Shareholders' equity (Details) (USD $)	12 Months Ended												1 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2010 Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2011 Series B Mandatory Convertible Non-cumulative Preferred Stock [Member]	Dec. 31, 2010 Series B Mandatory Convertible Non-cumulative Preferred Stock [Member]	Dec. 31, 2011 Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2010 Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2011 Series D Fixed Rate Non Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2010 Series D Fixed Rate Non Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2011 Ten Year Warrant Series A Preferred [Member]	Dec. 31, 2011 Ten Year Warrant Series C Preferred [Member]	May 31, 2011 Series A [Member]	Dec. 31, 2011 Series A [Member]	Dec. 31, 2011 Series B [Member]	Dec. 31, 2011 Series C [Member]	Dec. 31, 2011 Series D [Member]	Dec. 31, 2011 Preferred series A and C first five years [Member]	Dec. 31, 2011 Preferred series A and C after five years [Member]
Issued and outstanding preferred stock
Preferred stock, shares issued	381,500	778,000	230,000	600,000	0	26,500	151,500	151,500	50,000	0
Preferred stock, shares outstanding	50,000	0
Carrying value	$ 864,585,000	$ 740,657,000	$ 224,277,000	$ 578,630,000	$ 0	$ 26,500,000	$ 140,308,000	$ 135,527,000	$ 500,000,000	$ 0
Shareholders Equity (Textual) [Abstract]
Preferred stock, par value	$ 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
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	$ 0.7
Redemption days of shares by Company	90 days