cm:Level2TextBlock: us-gaap:InterestCostForPlantConstructionUsingIntermediaryPolicy
       
          
          | Interest Cost for Plant Construction Using Intermediary, Policy [Policy Text Block] | 
       
       
          
          | us-gaap:InterestCostForPlantConstructionUsingIntermediaryPolicy | 
       
       
          
          | Disclosure of accounting policy for electric utilities using an intermediary for plant construction. | 
       
       
          
          | cm:Level2TextBlock | 
       
       
          
          | Text Block (HTML) (nonnum:textBlockItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | (no balance type) | 
       
       
          
          | false | 
       
       
          
          | us-gaap:InterestCostForPlantConstructionUsingIntermediaryPolicy |