Regulatory Matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Ratio	4.50%
Ratio	6.00%
Ratio	8.00%
M&T (Consolidated) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 10,485,426
Ratio	11.08%
Minimum required amount	$ 4,259,977
Amount	$ 12,008,232	$ 9,644,765
Ratio	12.68%	12.47%
Minimum required amount	$ 5,679,969	$ 3,093,874
Amount	$ 14,128,454	$ 11,767,308
Ratio	14.92%	15.21%
Minimum required amount	$ 7,573,292	$ 6,187,747
Amount	$ 12,008,232	$ 9,644,765
Ratio	10.89%	10.17%
Minimum required amount	$ 4,408,971	$ 3,793,836
M&T Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 10,680,827
Ratio	11.33%
Minimum required amount	$ 4,242,817
Amount	$ 10,680,827	$ 8,043,185
Ratio	11.33%	10.46%
Minimum required amount	$ 5,657,089	$ 3,077,101
Amount	$ 12,589,917	$ 10,048,277
Ratio	13.35%	13.06%
Minimum required amount	$ 7,542,786	$ 6,154,201
Amount	$ 10,680,827	$ 8,043,185
Ratio	9.75%	8.56%
Minimum required amount	$ 4,381,617	$ 3,760,364
Wilmington Trust, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 476,106
Ratio	86.87%
Minimum required amount	$ 24,664
Amount	$ 476,106	$ 435,558
Ratio	86.87%	57.22%
Minimum required amount	$ 32,886	$ 30,447
Amount	$ 480,415	$ 439,867
Ratio	87.65%	57.79%
Minimum required amount	$ 43,848	$ 60,893
Amount	$ 476,106	$ 435,558
Ratio	22.38%	9.98%
Minimum required amount	$ 85,082	$ 174,613