REGULATORY ASSETS AND LIABILITIES - REGULATORY ASSETS (Details) - USD ($) $ in Millions |
Jun. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Regulatory assets | ||
| Regulatory assets | $ 449.5 | $ 446.2 |
| Environmental remediation costs | ||
| Regulatory assets | ||
| Regulatory assets | 128.9 | 133.5 |
| Plant retirement related items | ||
| Regulatory assets | ||
| Regulatory assets | 113.3 | 122.9 |
| Income tax related items | ||
| Regulatory assets | ||
| Regulatory assets | 61.6 | 59.3 |
| AROs | ||
| Regulatory assets | ||
| Regulatory assets | 60.7 | 49.1 |
| Electric transmission costs | ||
| Regulatory assets | ||
| Regulatory assets | 23.8 | 15.4 |
| Pension and OPEB costs | ||
| Regulatory assets | ||
| Regulatory assets | 12.0 | 19.8 |
| Finance and operating leases | ||
| Regulatory assets | ||
| Regulatory assets | 11.8 | 10.2 |
| Derivatives | ||
| Regulatory assets | ||
| Regulatory assets | 7.8 | 4.8 |
| Bluewater Natural Gas Holding, LLC | ||
| Regulatory assets | ||
| Regulatory assets | 6.6 | 8.7 |
| Other, net | ||
| Regulatory assets | ||
| Regulatory assets | $ 23.0 | $ 22.5 |