cm:Concept: us-gaap:OtherComprehensiveLossHeldToMaturitySecurityOttiAfterTaxAndAdjustmentsAttributableToNoncontrollingInterest
       
          
          | Other Comprehensive Loss, Held-to-maturity Security, OTTI, after Tax and Adjustments, Attributable to Noncontrolling Interest | 
       
       
          
          | us-gaap:OtherComprehensiveLossHeldToMaturitySecurityOttiAfterTaxAndAdjustmentsAttributableToNoncontrollingInterest | 
       
       
          
          | Amount, after tax and adjustments, of increase (decrease) in other than temporary impairment (OTTI) on investment in held-to-maturity security, recognized in other comprehensive loss and attributable to noncontrolling interest. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:OtherComprehensiveLossHeldToMaturitySecurityOttiAfterTaxAndAdjustmentsAttributableToNoncontrollingInterest |