cm:Concept: us-gaap:TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount
       
          
          | Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount | 
       
       
          
          | us-gaap:TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount | 
       
       
          
          | Carrying amount of liabilities associated with financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | As Of (instant) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount |