Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Offsetting [Abstract]
Reduction in estimated fair value of interest rate contracts in asset position	$ (136.2)
Reduction in estimated fair value of interest rate contracts in liability position	$ (12.2)

Increase (decrease) in estimated fair value of interest rate contracts in liability position.

No definition available.

Name:	mtb_IncreaseDecreaseInEstimatedFairValueOfInterestRateContractsInLiabilityPosition
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration