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Borrowings - Additional Information (Detail) - USD ($)
$ in Millions
6 Months Ended
Mar. 01, 2021
Jun. 30, 2021
Jan. 25, 2021
Debt Instrument [Line Items]      
Junior subordinated debentures   $ 530  
Debt Maturity, Start Year   Jan. 01, 2027  
Debt Maturity, End Year   Dec. 31, 2033  
M&T Bank Corporation [Member]      
Debt Instrument [Line Items]      
Variable rates senior notes amount     $ 350
Redeemed subordinated notes $ 500    
Maturity Date Dec. 01, 2021