cm:Concept: us-gaap:IncreaseDecreaseInPensionAndPostretirementObligations
       
          
          | Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits | 
       
       
          
          | us-gaap:IncreaseDecreaseInPensionAndPostretirementObligations | 
       
       
          
          | Amount of increase (decrease) in obligation for pension and other postretirement benefits. Includes, but is not limited to, defined benefit and defined contribution plans. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:IncreaseDecreaseInPensionAndPostretirementObligations |