cm:Concept: us-gaap:DefinedBenefitPlanCostOfProvidingSpecialOrContractualTerminationBenefitRecognizedDuringPeriod
| Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits |
| us-gaap:DefinedBenefitPlanCostOfProvidingSpecialOrContractualTerminationBenefitRecognizedDuringPeriod |
| Amount of cost of providing special or contractual termination benefits payable from defined benefit plan. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:DefinedBenefitPlanCostOfProvidingSpecialOrContractualTerminationBenefitRecognizedDuringPeriod |