cm:Concept: us-gaap:PaymentsForPurchaseOfSecuritiesOperatingActivities
       
          
          | Payments for Purchase of Securities, Operating Activities | 
       
       
          
          | us-gaap:PaymentsForPurchaseOfSecuritiesOperatingActivities | 
       
       
          
          | Cash paid to purchase debt and equity securities, classified as operating activities, during the period; includes trading securities and any other investments classified as operating. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:PaymentsForPurchaseOfSecuritiesOperatingActivities |