cm:Level3TextBlock: us-gaap:FDICIndemnificationAssetRollForwardTableTextBlock
       
          
          | FDIC Indemnification Asset Roll Forward [Table Text Block] | 
       
       
          
          | us-gaap:FDICIndemnificationAssetRollForwardTableTextBlock | 
       
       
          
          | Tabular disclosure of the change in the indemnification asset relating to loss sharing agreements with the Federal Deposit Insurance Corporation (FDIC). | 
       
       
          
          | cm:Level3TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:FDICIndemnificationAssetRollForwardTableTextBlock |