Amount of dividends available for payment to parent company after computation of banking subsidiaries earnings for the current year and preceding two years.

No definition available.

Name:	mtb_FundsAvailableForPaymentOfDividendsToParentCompanyFromBankingSubsidiaries
Namespace Prefix:	mtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Regulatory Matters - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Regulatory Capital Requirements [Abstract]
Funds available for payment of dividends to M&T from banking subsidiaries	$ 1,300
Required subsidiary noninterest-earning reserves against certain deposit liabilities			$ 666
Capital conservation buffer		2.50%