Regulatory Matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
M&T Bank Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 16,908	$ 15,562
Ratio	10.98%	10.44%
Amount	$ 18,918	$ 17,573
Ratio	0.1229	0.1179
Amount	$ 21,533	$ 20,260
Ratio	0.1399	0.136
Amount	$ 18,918	$ 17,573
Ratio	0.0943	0.0923
M&T Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 17,667	$ 16,674
Ratio	11.53%	11.23%
Amount	$ 17,667	$ 16,674
Ratio	0.1153	0.1123
Amount	$ 19,884	$ 18,888
Ratio	0.1297	0.1272
Amount	$ 17,667	$ 16,674
Ratio	0.0883	0.0877
Wilmington Trust, N.A. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 583	$ 586
Ratio	263.48%	254.50%
Amount	$ 583	$ 586
Ratio	2.6348	2.545
Amount	$ 584	$ 587
Ratio	2.6385	2.549
Amount	$ 583	$ 586
Ratio	0.86	0.8573