cm:Concept: us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
| Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate |
| us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate |
| Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. |
| cm:Concept |
| Percent (num:percentItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate |