cm:LineItems: us-gaap:SecuritizedAssetsAndAnyOtherFinancialAssetsManagedTogetherLineItems
       
          
          | Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items] | 
       
       
          
          | us-gaap:SecuritizedAssetsAndAnyOtherFinancialAssetsManagedTogetherLineItems | 
       
       
          
          | Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. | 
       
       
          
          | cm:LineItems | 
       
       
          
          | Text/String (xbrli:stringItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | true | 
       
       
          
          | us-gaap:SecuritizedAssetsAndAnyOtherFinancialAssetsManagedTogetherLineItems |