cm:Concept: us-gaap:IncreaseDecreaseInDeferredElectricCost
       
          
          | Increase (Decrease) in Deferred Electric Cost | 
       
       
          
          | us-gaap:IncreaseDecreaseInDeferredElectricCost | 
       
       
          
          | The increase (decrease) during the reporting period in carrying amount of capitalized electric costs of a regulated entity that are expected to be recoverable through rate adjustments within one year or the normal operating cycle, if longer. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:IncreaseDecreaseInDeferredElectricCost |