REGULATORY ASSETS AND LIABILITIES - REGULATORY LIABILITIES (Details) - USD ($) $ in Millions |
Sep. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Regulatory liabilities | ||
| Amounts refundable to customers | $ 23.7 | $ 11.4 |
| Regulatory liabilities | 644.0 | 643.4 |
| Total regulatory liabilities | 667.7 | 654.8 |
| Income tax related items | ||
| Regulatory liabilities | ||
| Total regulatory liabilities | 293.5 | 305.9 |
| Removal costs | ||
| Regulatory liabilities | ||
| Total regulatory liabilities | 227.6 | 219.4 |
| Pension and OPEB benefits | ||
| Regulatory liabilities | ||
| Total regulatory liabilities | 85.9 | 85.7 |
| Energy costs refundable through rate adjustments | ||
| Regulatory liabilities | ||
| Total regulatory liabilities | 23.7 | 11.4 |
| Derivatives | ||
| Regulatory liabilities | ||
| Total regulatory liabilities | 11.3 | 8.3 |
| Other, net | ||
| Regulatory liabilities | ||
| Total regulatory liabilities | $ 25.7 | $ 24.1 |