cm:Concept: us-gaap:SecuritiesPurchasedUnderAgreementsToResellMeasurementDifferenceDescription
       
          
          | Securities Purchased under Agreements to Resell, Measurement Difference Description | 
       
       
          
          | us-gaap:SecuritiesPurchasedUnderAgreementsToResellMeasurementDifferenceDescription | 
       
       
          
          | Description of measurement difference between recognized amounts and resulting measurement differences for securities purchased under agreement to resell. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Text/String (xbrli:stringItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:SecuritiesPurchasedUnderAgreementsToResellMeasurementDifferenceDescription |