cm:Concept: us-gaap:PaymentToAcquireLifeInsurancePolicyOperatingActivities
       
          
          | Payment to Acquire Life Insurance Policy, Operating Activities | 
       
       
          
          | us-gaap:PaymentToAcquireLifeInsurancePolicyOperatingActivities | 
       
       
          
          | Amount of cash outflow for payment of premium on corporate-owned life insurance policy, classified as operating activities. Includes, but is not limited to, bank-owned life insurance policy. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:PaymentToAcquireLifeInsurancePolicyOperatingActivities |