Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Parenthetical) (Detail) $ in Millions	Jun. 30, 2017 USD ($)
Offsetting [Abstract]
Reduction in estimated fair value of interest rate swaps in asset position	$ (91.7)
Reduction in estimated fair value of interest rate swaps in liability position	$ (32.0)

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

No definition available.

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