Regulatory Matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
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	$ 10,849,642	$ 10,485,426
Ratio	10.70%	11.08%
Minimum required amount	$ 5,195,288	$ 4,259,977
Amount	$ 12,083,948	$ 12,008,232
Ratio	11.92%	12.68%
Minimum required amount	$ 6,715,859	$ 5,679,969
Amount	$ 14,282,492	$ 14,128,454
Ratio	14.09%	14.92%
Minimum required amount	$ 8,743,289	$ 7,573,292
Amount	$ 12,083,948	$ 12,008,232
Ratio	9.99%	10.89%
Minimum required amount	$ 4,836,901	$ 4,408,971
M&T Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 10,115,688	$ 10,680,827
Ratio	10.02%	11.33%
Minimum required amount	$ 5,175,310	$ 4,242,817
Amount	$ 10,115,688	$ 10,680,827
Ratio	10.02%	11.33%
Minimum required amount	$ 6,690,035	$ 5,657,089
Amount	$ 11,812,114	$ 12,589,917
Ratio	11.70%	13.35%
Minimum required amount	$ 8,709,668	$ 7,542,786
Amount	$ 10,115,688	$ 10,680,827
Ratio	8.41%	9.75%
Minimum required amount	$ 4,812,685	$ 4,381,617
Wilmington Trust, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 496,801	$ 476,106
Ratio	57.08%	86.87%
Minimum required amount	$ 44,607	$ 24,664
Amount	$ 496,801	$ 476,106
Ratio	57.08%	86.87%
Minimum required amount	$ 57,662	$ 32,886
Amount	$ 501,111	$ 480,415
Ratio	57.57%	87.65%
Minimum required amount	$ 75,070	$ 43,848
Amount	$ 496,801	$ 476,106
Ratio	15.31%	22.38%
Minimum required amount	$ 129,774	$ 85,082