cm:Concept: us-gaap:ProceedsFromCollectionOfRetainedInterestInSecuritizedReceivablesCategorizedAsHeldToMaturity
       
          
          | Proceeds from Collection of Retained Interest in Securitized Receivables categorized as Held-to-maturity | 
       
       
          
          | us-gaap:ProceedsFromCollectionOfRetainedInterestInSecuritizedReceivablesCategorizedAsHeldToMaturity | 
       
       
          
          | Amount of cash inflow from collection on beneficial interest in securitization of loan receivable measured at amortized cost. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ProceedsFromCollectionOfRetainedInterestInSecuritizedReceivablesCategorizedAsHeldToMaturity |