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Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
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Mar. 31, 2024 | Dec. 31, 2023
Offsetting [Abstract] |  |
Reduction in estimated fair value of interest rate contracts in asset position | $ 893 | $ 783
Reduction in estimated fair value of interest rate contracts in liability position | $ 16 | $ 32

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- Definition Increase (decrease) in estimated fair value of interest rate contracts in asset position. + References No definition available. + Details
Name: | mtb_IncreaseDecreaseInEstimatedFairValueOfInterestRateContractsInAssetPosition
Namespace Prefix: | mtb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Increase (decrease) in estimated fair value of interest rate contracts in liability position. + References No definition available. + Details
Name: | mtb_IncreaseDecreaseInEstimatedFairValueOfInterestRateContractsInLiabilityPosition
Namespace Prefix: | mtb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_OffsettingAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration