cm:Concept: us-gaap:ContingentlyConvertibleSecuritiesIncludedInDilutedEarningsPerShare
       
          
          | Contingently Convertible Securities Included in Diluted Earnings Per Share [true false] | 
       
          
          | us-gaap:ContingentlyConvertibleSecuritiesIncludedInDilutedEarningsPerShare | 
       
          
          | Indicates (true false) whether share issuable in conversion of contingently convertible security is included in calculation of diluted earnings per share. | 
       
          
          | cm:Concept | 
       
          
          | Yes/No (xbrli:booleanItemType) | 
       
          
          | For Period (duration) | 
       
          
          | (no balance type) | 
       
          
          | false | 
       
          
          | us-gaap:ContingentlyConvertibleSecuritiesIncludedInDilutedEarningsPerShare |