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EMPLOYEE BENEFITS-COSTS AND CONTRIBUTIONS (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023
Components of net periodic benefit cost (credit) |  |  |
Contributions and payments related to pension and OPEB plans | $ 4.0 | $ 5.5 |
Total regulatory assets | 3,286.9 |  | $ 3,274.7
Pension Benefits |  |  |
Components of net periodic benefit cost (credit) |  |  |
Service cost | 6.7 | 6.6 |
Interest cost | 29.5 | 30.8 |
Expected return on plan assets | (45.8) | (47.4) |
Amortization of prior service (credit) cost | 0.0 | 0.1 |
Amortization of net actuarial (gain) loss | 14.4 | 7.4 |
Net periodic benefit (credit) cost | 4.8 | (2.5) |
Contributions and payments related to pension and OPEB plans | 3.7 |  |
Estimated future employer contributions for the remainder of the year | 9.5 |  |
Pension Benefits | Pension and Other Postretirement Plans Cost |  |  |
Components of net periodic benefit cost (credit) |  |  |
Total regulatory assets | 10.8 |  |
Other Postretirement Benefits |  |  |
Components of net periodic benefit cost (credit) |  |  |
Service cost | 2.8 | 2.5 |
Interest cost | 5.7 | 5.4 |
Expected return on plan assets | (13.2) | (13.3) |
Amortization of prior service (credit) cost | (3.4) | (3.7) |
Amortization of net actuarial (gain) loss | (1.9) | (3.2) |
Net periodic benefit (credit) cost | (10.0) | $ (12.3) |
Contributions and payments related to pension and OPEB plans | 0.3 |  |
Estimated future employer contributions for the remainder of the year | 1.9 |  |
Other Postretirement Benefits | Pension and Other Postretirement Plans Cost |  |  |
Components of net periodic benefit cost (credit) |  |  |
Total regulatory assets | $ 20.7 |  |

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