cm:Concept: us-gaap:TransfersOfFinancialAssetsAccountedForAsSaleInitialFairValueOfAssetsObtainedAsProceeds
       
          
          | Transfers of Financial Assets Accounted for as Sale, Initial Fair Value of Assets Obtained as Proceeds | 
       
       
          
          | us-gaap:TransfersOfFinancialAssetsAccountedForAsSaleInitialFairValueOfAssetsObtainedAsProceeds | 
       
       
          
          | Represents the initial fair value recorded for assets received on transfer of financial assets in a securitization, asset-backed financing arrangement, or a similar transfer which transaction is recognized as a sale of the transferred financial assets. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | As Of (instant) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:TransfersOfFinancialAssetsAccountedForAsSaleInitialFairValueOfAssetsObtainedAsProceeds |