Regulatory matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
M&T (Consolidated) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount, Tier 1 capital	$ 7,810,196	$ 6,926,218
Ratio, Tier 1 capital	10.22%	9.67%
Minimum required amount, Tier 1 capital	3,057,093	2,864,002
Amount, Total capital	10,230,302	9,493,124
Ratio, Total capital	13.39%	13.26%
Minimum required amount, Total capital	6,114,186	5,728,005
Amount, Leverage	7,810,196	6,926,218
Ratio, Leverage	10.07%	9.28%
Minimum required amount, Leverage	2,327,122	2,239,639
M&T Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount, Tier 1 capital	6,767,774	6,283,825
Ratio, Tier 1 capital	8.92%	8.87%
Minimum required amount, Tier 1 capital	3,034,184	2,832,558
Amount, Total capital	8,981,931	8,587,360
Ratio, Total capital	11.84%	12.13%
Minimum required amount, Total capital	6,068,367	5,665,116
Amount, Leverage	6,767,774	6,283,825
Ratio, Leverage	8.84%	8.54%
Minimum required amount, Leverage	2,297,902	2,206,498
Wilmington Trust, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount, Tier 1 capital	405,469	393,360
Ratio, Tier 1 capital	61.02%	71.89%
Minimum required amount, Tier 1 capital	26,580	21,887
Amount, Total capital	410,873	399,177
Ratio, Total capital	61.83%	72.95%
Minimum required amount, Total capital	53,160	43,774
Amount, Leverage	405,469	393,360
Ratio, Leverage	21.62%	19.20%
Minimum required amount, Leverage	$ 56,275	$ 61,478