Investment Securities - Amortized Cost and Estimated Fair Value of Collateralized Mortgage Obligations (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Amortized Cost And Fair Value Debt Securities [Abstract]
Collateralized mortgage obligations, Amortized cost	$ 61,980	$ 77,964
Collateralized mortgage obligations, Estimated fair value	$ 57,763	$ 71,099

Fair value of collateralized mortgage obligations included in mortgage-backed securities.

No definition available.

Name:	mtb_CollateralizedMortgageObligationsEstimatedFairValue
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant