Regulatory Matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) $ in Thousands	Dec. 31, 2022 USD ($)	Sep. 30, 2022	Dec. 31, 2021 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Ratio		2.50%
M&T Bank Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 15,562,037,000		$ 11,844,833
Ratio	10.44%		13.11%
Amount	$ 17,572,586,000		$ 13,594,782
Ratio	0.1179		0.1142
Amount	$ 20,259,735,000		$ 15,902,833
Ratio	0.1360		0.1533
Amount	$ 17,572,586,000		$ 13,594,782,000
Ratio	0.0923		0.0887
M&T Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 16,673,578,000		$ 12,378,354
Ratio	11.23%		11.98%
Amount	$ 16,673,578,000		$ 12,378,354
Ratio	0.1123		0.1198
Amount	$ 18,887,691,000		$ 14,170,434
Ratio	0.1272		0.1371
Amount	$ 16,673,578,000		$ 12,378,354,000
Ratio	0.0877		0.0811
Wilmington Trust, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 585,968,000		$ 779,521
Ratio	254.50%		31.22%
Amount	$ 585,968,000		$ 779,521
Ratio			0.3122
Ratio	2.5450
Amount	$ 586,879,000		$ 780,791
Ratio			0.3127
Ratio	2.5490
Amount	$ 585,968,000		$ 779,521,000
Ratio	0.8573		0.0623