Regulatory Matters - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Banking And Thrift [Abstract]
Funds available for payment of dividends to M&T from banking subsidiaries	$ 605
Required subsidiary noninterest-earning reserves against certain deposit liabilities	$ 666		$ 684
Capital conservation buffer		2.50%

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