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Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) (Fixed Rate Long-Term Borrowings [Member], Fair Value Hedges [Member], USD $)
3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Fixed Rate Long-Term Borrowings [Member] | Fair Value Hedges [Member]
   
Derivative [Line Items]    
Notional Amount $ 1,400,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= mtb_FixedRateLongTermBorrowingsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
$ 1,400,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= mtb_FixedRateLongTermBorrowingsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
Average Maturity (in years) 2 years 4 months 24 days 2 years 8 months 12 days
Weighted-Average Rate, Fixed 4.42%us-gaap_DerivativeAverageFixedInterestRate
/ us-gaap_DerivativeByNatureAxis
= mtb_FixedRateLongTermBorrowingsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
4.42%us-gaap_DerivativeAverageFixedInterestRate
/ us-gaap_DerivativeByNatureAxis
= mtb_FixedRateLongTermBorrowingsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
Weighted-Average Rate, Variable 1.22%us-gaap_DerivativeAverageVariableInterestRate
/ us-gaap_DerivativeByNatureAxis
= mtb_FixedRateLongTermBorrowingsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
1.19%us-gaap_DerivativeAverageVariableInterestRate
/ us-gaap_DerivativeByNatureAxis
= mtb_FixedRateLongTermBorrowingsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember