cm:Concept: us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities
       
          
          | Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities | 
       
       
          
          | us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities | 
       
       
          
          | The cash inflow associated with the maturity, prepayments and calls (requests for early payments) of debt securities designated as held-to-maturity. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities |