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Acquisitions - Additional Information (Detail) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Aug. 27, 2012
Business Acquisition [Line Items]      
Purchase consideration per common share     $ 0.08403us-gaap_BusinessAcquisitionSharePrice
Percentage of total equity consideration     60.00%mtb_PurchaseConsiderationEquityPercentage
Percentage of total cash consideration     40.00%mtb_PurchaseConsiderationCashPercentage
Total consideration to be paid $ 5,500,000,000mtb_BusinessAcquisitionContingentConsiderationAtFairValue1    
Assets 98,377,783,000us-gaap_Assets 96,685,535,000us-gaap_Assets  
Loans 66,177,669,000us-gaap_LoansAndLeasesReceivableNetReportedAmount 65,749,394,000us-gaap_LoansAndLeasesReceivableNetReportedAmount  
Liabilities 85,849,482,000us-gaap_Liabilities 84,349,639,000us-gaap_Liabilities  
Deposits 73,594,120,000us-gaap_Deposits 73,582,053,000us-gaap_Deposits  
Hudson City [Member]      
Business Acquisition [Line Items]      
Assets 36,100,000,000us-gaap_Assets
/ us-gaap_BusinessAcquisitionAxis
= mtb_HudsonCityMember
   
Loans 20,900,000,000us-gaap_LoansAndLeasesReceivableNetReportedAmount
/ us-gaap_BusinessAcquisitionAxis
= mtb_HudsonCityMember
   
Investment securities 8,300,000,000us-gaap_MarketableSecurities
/ us-gaap_BusinessAcquisitionAxis
= mtb_HudsonCityMember
   
Liabilities 31,300,000,000us-gaap_Liabilities
/ us-gaap_BusinessAcquisitionAxis
= mtb_HudsonCityMember
   
Deposits $ 18,900,000,000us-gaap_Deposits
/ us-gaap_BusinessAcquisitionAxis
= mtb_HudsonCityMember