cm:Concept: us-gaap:ProceedsFromPaymentsForInInterestBearingDepositsInBanks
       
          
          | Proceeds from (Payments for) in Interest-bearing Deposits in Banks | 
       
       
          
          | us-gaap:ProceedsFromPaymentsForInInterestBearingDepositsInBanks | 
       
       
          
          | The net cash inflow or outflow in Interest-bearing Deposits by banks in other financial institutions for relatively short periods of time including, for example, certificates of deposits. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ProceedsFromPaymentsForInInterestBearingDepositsInBanks |