cm:Concept: us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfMortgageBackedSecuritiesMBS
       
          
          | Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS) | 
       
       
          
          | us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfMortgageBackedSecuritiesMBS | 
       
       
          
          | The cash inflow from the maturity (principal due), prepayment and call (request of early payment) of a loan financed by home mortgage payments classified as held to maturity. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfMortgageBackedSecuritiesMBS |