cm:Concept: us-gaap:DefinedBenefitPlanTransfersBetweenMeasurementLevels
| Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Assets Transferred into (out of) Level 3 |
| us-gaap:DefinedBenefitPlanTransfersBetweenMeasurementLevels |
| Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:DefinedBenefitPlanTransfersBetweenMeasurementLevels |