Regulatory Matters - Summary of Required Minimum and Well Capitalized Capital Ratios (Detail)	Dec. 31, 2022	Sep. 30, 2022
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 ("CET1") to risk-weighted assets, Minimum		2.50%
M&T (Consolidated) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 ("CET1") to risk-weighted assets, Minimum	4.50%
Tier 1 capital to risk-weighted assets, Minimum	0.060
Total capital to risk-weighted assets, Minimum	0.080
Leverage - Tier 1 capital to average total assets, as defined	0.040
Tier 1 capital to risk-weighted assets, Well capitalized	0.060
Total capital to risk-weighted assets, Well capitalized	0.100
Bank Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 ("CET1") to risk-weighted assets, Minimum	4.50%
Tier 1 capital to risk-weighted assets, Minimum	0.060
Total capital to risk-weighted assets, Minimum	0.080
Leverage - Tier 1 capital to average total assets, as defined	0.040
Common equity Tier 1 ("CET1") to risk-weighted assets, Well Capitalized	6.50%
Tier 1 capital to risk-weighted assets, Well capitalized	0.080
Total capital to risk-weighted assets, Well capitalized	0.100
Leverage - Tier 1 capital to average total assets, as defined	0.050