cm:Concept: us-gaap:DefinedBenefitPlanCurtailments
| Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment |
| us-gaap:DefinedBenefitPlanCurtailments |
| Amount of (increase) decrease in benefit obligation of defined benefit plan from event reducing expected years of future service of present employees or eliminating accrual of benefits for some or all future services of present employees. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:DefinedBenefitPlanCurtailments |