Regulatory Matters - Capital Ratios and Amounts of Company and its Banking Subsidiaries (Detail) $ in Millions	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
M&T
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 18,299	$ 16,908
Ratio	0.1168	0.1098
Amount	$ 20,692	$ 18,918
Ratio	0.1321	0.1229
Amount	$ 23,073	$ 21,533
Ratio	0.1473	0.1399
Amount	$ 20,692	$ 18,918
Ratio	0.1017	0.0943
M&T Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 19,233	$ 17,667
Ratio	0.1232	0.1153
Amount	$ 19,233	$ 17,667
Ratio	0.1232	0.1153
Amount	$ 21,387	$ 19,884
Ratio	0.1370	0.1297
Amount	$ 19,233	$ 17,667
Ratio	0.0948	0.0883
Wilmington Trust, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount	$ 603	$ 583
Ratio	2.6964	2.6348
Amount	$ 603	$ 583
Ratio	2.6964	2.6348
Amount	$ 604	$ 584
Ratio	2.6988	2.6385
Amount	$ 603	$ 583
Ratio	0.8337	0.8600