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EMPLOYEE BENEFITS-COSTS AND CONTRIBUTIONS (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025 | Dec. 31, 2025
Components of net periodic benefit cost (credit) |  |  |  |  |
Contributions and payments related to pension and OPEB plans |  |  | $ 7.2 | $ 7.1 |
Regulatory assets | $ 3,169.1 |  | 3,169.1 |  | $ 3,173.6
Regulatory liabilities | 4,325.5 |  | 4,325.5 |  | 4,210.2
Pension Benefits |  |  |  |  |
Components of net periodic benefit cost (credit) |  |  |  |  |
Service cost | 5.1 | $ 4.8 | 11.2 | 10.5 |
Interest cost | 28.6 | 29.1 | 57.2 | 59.4 |
Expected return on plan assets | (42.6) | (43.6) | (85.4) | (87.7) |
Amortization of prior service credit | (0.1) | (0.1) | (0.1) | (0.1) |
Amortization of net actuarial (gain) loss | 10.9 | 9.5 | 21.3 | 23.1 |
Net periodic benefit (credit) cost | 1.9 | (0.3) | 4.2 | 5.2 |
Contributions and payments related to pension and OPEB plans |  |  | 6.1 |  |
Estimated future employer contributions for the remainder of the year | 5.7 |  | 5.7 |  |
Pension Benefits | Pension and Other Postretirement Plans Cost |  |  |  |  |
Components of net periodic benefit cost (credit) |  |  |  |  |
Regulatory liabilities | 19.3 |  | 19.3 |  | 14.7
Other Postretirement Benefits |  |  |  |  |
Components of net periodic benefit cost (credit) |  |  |  |  |
Service cost | 3.1 | 2.8 | 6.2 | 5.6 |
Interest cost | 6.5 | 6.3 | 13.2 | 12.8 |
Expected return on plan assets | (14.5) | (13.5) | (28.9) | (27.1) |
Amortization of prior service credit | (1.5) | (1.8) | (2.6) | (5.0) |
Amortization of net actuarial (gain) loss | (2.4) | (2.3) | (4.1) | (3.7) |
Net periodic benefit (credit) cost | (8.8) | $ (8.5) | (16.2) | $ (17.4) |
Contributions and payments related to pension and OPEB plans |  |  | 1.1 |  |
Estimated future employer contributions for the remainder of the year | 1.2 |  | 1.2 |  |
Other Postretirement Benefits | Pension and Other Postretirement Plans Cost |  |  |  |  |
Components of net periodic benefit cost (credit) |  |  |  |  |
Regulatory assets | $ 7.9 |  | $ 7.9 |  | $ 0.7

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