cm:Concept: us-gaap:IncreaseDecreaseInFinancialInstrumentsUsedInOperatingActivities
       
          
          | Increase (Decrease) in Financial Instruments Used in Operating Activities | 
       
       
          
          | us-gaap:IncreaseDecreaseInFinancialInstrumentsUsedInOperatingActivities | 
       
       
          
          | The increase (decrease) during the reporting period in the aggregate value of financial instruments used in operating activities, including trading securities, risk management instruments, and other short-term trading instruments. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:IncreaseDecreaseInFinancialInstrumentsUsedInOperatingActivities |