cm:Concept: us-gaap:GainLossOnSaleOfOtherLoansAndLeases
       
          
          | Gain (Loss) on Sale of Other Loans and Leases | 
       
       
          
          | us-gaap:GainLossOnSaleOfOtherLoansAndLeases | 
       
       
          
          | The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of other loans and leases that were sold during the reporting period; excludes gains (losses) on sales of consumer and mortgage loans. This element refers to the gain (loss) and not to the cash proceeds of the sales. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:GainLossOnSaleOfOtherLoansAndLeases |