cm:Level3TextBlock: us-gaap:ScheduleOfQuantitativeInformationAboutFinancialAssetsAndAssociatedLiabilitiesAccountedForAsSecuredBorrowingsTextBlock
       
          
          | Schedule of Assets and Associated Liabilities Accounted for as Secured Borrowings [Table Text Block] | 
       
       
          
          | us-gaap:ScheduleOfQuantitativeInformationAboutFinancialAssetsAndAssociatedLiabilitiesAccountedForAsSecuredBorrowingsTextBlock | 
       
       
          
          | Tabular disclosure of the carrying amount and classification of assets and liabilities recognized in the transferor's statement of financial position at the end of each period presented. | 
       
       
          
          | cm:Level3TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ScheduleOfQuantitativeInformationAboutFinancialAssetsAndAssociatedLiabilitiesAccountedForAsSecuredBorrowingsTextBlock |