cm:Level3TextBlock: us-gaap:FinancialGuaranteeInsuranceContractsClaimLiabilityTableTextBlock
       
          
          | Financial Guarantee Insurance Contracts, Claim Liability [Table Text Block] | 
       
       
          
          | us-gaap:FinancialGuaranteeInsuranceContractsClaimLiabilityTableTextBlock | 
       
       
          
          | Tabular disclosure of the claim liability for financial guarantee insurance contracts. | 
       
       
          
          | cm:Level3TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:FinancialGuaranteeInsuranceContractsClaimLiabilityTableTextBlock |