cm:Concept: us-gaap:CoalIndustryRetireeHealthBenefitActOf1992EstimatedAmountOfTotalObligation
| Coal Industry Retiree Health Benefit Act of 1992, Estimated Amount of Obligation |
| us-gaap:CoalIndustryRetireeHealthBenefitActOf1992EstimatedAmountOfTotalObligation |
| Amount of obligation for medical and death benefits to be provided under Coal Industry Retiree Health Benefit Act of 1992. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Credit |
| false |
| us-gaap:CoalIndustryRetireeHealthBenefitActOf1992EstimatedAmountOfTotalObligation |