cm:Concept: us-gaap:UtilitiesOperatingExpensePurchasedPowerUnderLongTermContracts
| Utilities Operating Expense, Purchased Power under Long-term Contracts |
| us-gaap:UtilitiesOperatingExpensePurchasedPowerUnderLongTermContracts |
| Amount of operating expense for purchased power procured under arrangements extending beyond one year or the normal operating cycle, if longer, by regulated operation. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:UtilitiesOperatingExpensePurchasedPowerUnderLongTermContracts |