cm:Level3TextBlock: us-gaap:ShortdurationInsuranceContractsScheduleOfHistoricalClaimsDurationTableTextBlock
       
          
          | Short-duration Insurance Contracts, Schedule of Historical Claims Duration [Table Text Block] | 
       
       
          
          | us-gaap:ShortdurationInsuranceContractsScheduleOfHistoricalClaimsDurationTableTextBlock | 
       
       
          
          | Tabular disclosure of average annual percentage payout of incurred claims by age, after reinsurance, for short-duration insurance contracts. | 
       
       
          
          | cm:Level3TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:ShortdurationInsuranceContractsScheduleOfHistoricalClaimsDurationTableTextBlock |