cm:Concept: us-gaap:MultiemployerPlansAccumulatedBenefitObligation
| Multiemployer Plans, Accumulated Benefit Obligation |
| us-gaap:MultiemployerPlansAccumulatedBenefitObligation |
| Amount of accumulated benefit obligation attributable to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Credit |
| false |
| us-gaap:MultiemployerPlansAccumulatedBenefitObligation |