cm:Concept: us-gaap:AmortizationAndDepreciationOfDecontaminatingAndDecommissioningAssets
| Amortization and Depreciation of Decontaminating and Decommissioning Assets |
| us-gaap:AmortizationAndDepreciationOfDecontaminatingAndDecommissioningAssets |
| The current period expense charged against earnings on decontaminating and decommissioning of facilities used in the normal conduct of business and not intended for resale to allocate or recognize the cost of the assets over their useful lives. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:AmortizationAndDepreciationOfDecontaminatingAndDecommissioningAssets |