v3.26.1
Fair value measurements (Details) - EBP 004 - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value $ 5,400,433 $ 5,104,529
Fair Value, Inputs, Level 1, Level 2, and Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 493,585 489,476
Fair Value, Inputs, Level 1, Level 2, and Level 3 | M&T Bank Corporation common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 447,557 441,099
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 46,028 48,377
Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 493,585 489,476
Level 1 | M&T Bank Corporation common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 447,557 441,099
Level 1 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 46,028 48,377
Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 2 | M&T Bank Corporation common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 2 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3 | M&T Bank Corporation common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
Level 3 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value 0 0
NAV    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments, at fair value $ 4,906,848 $ 4,615,053