cm:Concept: us-gaap:ProceedsFromIssuanceOfSubordinatedLongTermDebt
       
          
          | Proceeds from Issuance of Subordinated Long-term Debt | 
       
       
          
          | us-gaap:ProceedsFromIssuanceOfSubordinatedLongTermDebt | 
       
       
          
          | The cash inflow from a borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in liquidation of the entity's assets or underlying collateral. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ProceedsFromIssuanceOfSubordinatedLongTermDebt |