cm:Level3TextBlock: us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTableTextBlock
       
          
          | Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Table Text Block] | 
       
       
          
          | us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTableTextBlock | 
       
       
          
          | Tabular disclosure of financial guarantee insurance contracts in which premiums are received over the contract period. | 
       
       
          
          | cm:Level3TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTableTextBlock |