cm:Level3TextBlock: us-gaap:ScheduleOfGainLossOnSecuritizationsOfFinancialAssetsAccountedForAsSaleTextBlock
       
          
          | Schedule of Gain (Loss) on Securitizations or Asset-backed Financing Arrangements of Financial Assets Accounted for as Sale [Table Text Block] | 
       
       
          
          | us-gaap:ScheduleOfGainLossOnSecuritizationsOfFinancialAssetsAccountedForAsSaleTextBlock | 
       
       
          
          | Tabular disclosure of amounts pertaining to the excess over or deficiency from the carrying amounts of financial assets which are recognized upon the sale of financial assets. | 
       
       
          
          | cm:Level3TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ScheduleOfGainLossOnSecuritizationsOfFinancialAssetsAccountedForAsSaleTextBlock |