cm:Level3TextBlock: us-gaap:OtherRealEstateRollForwardTableTextBlock
       
          
          | Other Real Estate, Roll Forward [Table Text Block] | 
       
       
          
          | us-gaap:OtherRealEstateRollForwardTableTextBlock | 
       
       
          
          | Tabular disclosure of the change in other real estate on properties owned. Excludes real estate assets taken in settlement of troubled loans through surrender or foreclosure by banks. | 
       
       
          
          | cm:Level3TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:OtherRealEstateRollForwardTableTextBlock |