cm:Member: us-gaap:FinancialAssetsSoldUnderAgreementToRepurchaseMember
       
          
          | Financial Assets Sold under Agreement to Repurchase [Member] | 
       
       
          
          | us-gaap:FinancialAssetsSoldUnderAgreementToRepurchaseMember | 
       
       
          
          | Agreement under which the transferor transfers a financial asset to a transferee in exchange for cash and concurrently agrees to reacquire that financial asset at a future date. | 
       
       
          
          | cm:Member | 
       
       
          
          | [Member] (nonnum:domainItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | true | 
       
       
          
          | us-gaap:FinancialAssetsSoldUnderAgreementToRepurchaseMember |