cm:Concept: us-gaap:HeldtomaturitySecuritiesTransferredToTradingSecuritiesUnrealizedGainLossExcludingOtherThanTemporaryImpairments
       
          
          | Debt Securities, Held-to-maturity, Transfer to Trading, Unrealized Gain (Loss), Excluding Other-than-temporary Impairment | 
       
       
          
          | us-gaap:HeldtomaturitySecuritiesTransferredToTradingSecuritiesUnrealizedGainLossExcludingOtherThanTemporaryImpairments | 
       
       
          
          | Amount of unrealized gain (loss) recognized in earnings from transfer of investment in debt security measured at amortized cost (held-to-maturity), to investment in debt security measured at fair value with change in fair value recognized in net income (trading). Excludes other-than-temporary impairment (OTTI) previously recognized in other comprehensive income (OCI). | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:HeldtomaturitySecuritiesTransferredToTradingSecuritiesUnrealizedGainLossExcludingOtherThanTemporaryImpairments |