cm:Concept: us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax
       
          
          | Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax | 
       
       
          
          | us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax | 
       
       
          
          | Amount, after tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | As Of (instant) | 
       
       
          
          | Credit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax |