cm:Concept: us-gaap:ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments
       
          
          | Servicing Asset at Amortized Cost, Other than Temporary Impairments | 
       
       
          
          | us-gaap:ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments | 
       
       
          
          | Amount of other-than-temporary impairment (OTTI) applied to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments |