Regulatory Matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
M&T Bank Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 11,844,833	$ 10,623,368
Ratio	11.42%	10.00%
Amount	$ 13,594,782	$ 11,873,317
Ratio	0.1311	0.1117
Amount	$ 15,902,833	$ 14,207,937
Ratio	0.1533	0.1337
Amount	$ 13,594,782	$ 11,873,317
Ratio	0.0887	0.0848
M&T Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 12,378,354	$ 11,550,462
Ratio	11.98%	10.90%
Amount	$ 12,378,354	$ 11,550,462
Ratio	0.1198	0.1090
Amount	$ 14,170,434	$ 13,373,416
Ratio	0.1371	0.1262
Amount	$ 12,378,354	$ 11,550,462
Ratio	0.0811	0.0827
Wilmington Trust, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 779,521	$ 630,574
Ratio	31.22%	46.57%
Amount	$ 779,521	$ 630,574
Ratio	0.3122	0.4657
Amount	$ 780,791	$ 632,506
Ratio	0.3127	0.4672
Amount	$ 779,521	$ 630,574
Ratio	0.0623	0.1073