cm:Member: us-gaap:AccumulatedOtherthanTemporaryImpairmentIncludingPortionAttributableToNoncontrollingInterestMember
       
          
          | Accumulated Other-than-Temporary Impairment Including Portion Attributable to Noncontrolling Interest [Member] | 
       
       
          
          | us-gaap:AccumulatedOtherthanTemporaryImpairmentIncludingPortionAttributableToNoncontrollingInterestMember | 
       
       
          
          | Accumulated other comprehensive loss resulting from other-than-temporary impairments (OTTI) of debt securities if a portion of an other-than-temporary impairment has not been recognized in earnings, including the portion attributable to the noncontrolling interest. | 
       
       
          
          | cm:Member | 
       
       
          
          | [Member] (nonnum:domainItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | true | 
       
       
          
          | us-gaap:AccumulatedOtherthanTemporaryImpairmentIncludingPortionAttributableToNoncontrollingInterestMember |