cm:Concept: us-gaap:DefinedBenefitPlanPlanAssetsFairValueByHierarchyAndNavExtensibleList
| Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List] |
| us-gaap:DefinedBenefitPlanPlanAssetsFairValueByHierarchyAndNavExtensibleList |
| Indicates level within fair value hierarchy and fair value measured at net asset value per share as practical expedient, of defined benefit plan asset. |
| cm:Concept |
| srt-types:extensibleListItemType |
| As Of (instant) |
| (no balance type) |
| false |
| us-gaap:DefinedBenefitPlanPlanAssetsFairValueByHierarchyAndNavExtensibleList |