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EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Pension and SERP |  |
Net Regulatory Assets [Abstract] |  |
Actuarial (Gain)/Loss Arising During the Year | $ 251.1 | $ (431.6)
Actuarial Loss Reclassified as Net Periodic Benefit Expense | (38.8) | (107.0)
Settlement Loss | 0.0 | 0.0
Prior Service Credit Arising During the Year | 0.0 | 0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | (1.2) | (1.2)
Actuarial Loss | 1,101.0 | 888.7
Prior Service (Credit)/Cost | 2.9 | 4.1
OCI |  |
Actuarial (Gain)/Loss Arising During the Year | 14.0 | 4.6
Actuarial Loss Reclassified as Net Periodic Benefit Expense | (7.0) | (9.0)
Settlement Loss | (12.4) | 0.0
Prior Service Credit Arising During the Year | 0.0 | 0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | (0.1) | (0.2)
Actuarial Loss | 56.5 | 61.9
Prior Service Cost | 0.3 | 0.4
PBOP |  |
Net Regulatory Assets [Abstract] |  |
Actuarial (Gain)/Loss Arising During the Year | (32.0) | 36.8
Actuarial Loss Reclassified as Net Periodic Benefit Expense | 0.0 | 0.0
Settlement Loss | 0.0 | 0.0
Prior Service Credit Arising During the Year | (0.9) | 0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | 21.8 | 21.8
Actuarial Loss | 49.8 | 81.8
Prior Service (Credit)/Cost | (87.4) | (108.3)
OCI |  |
Actuarial (Gain)/Loss Arising During the Year | (0.3) | (0.8)
Actuarial Loss Reclassified as Net Periodic Benefit Expense | 0.0 | 0.0
Settlement Loss | 0.0 | 0.0
Prior Service Credit Arising During the Year | 0.0 | 0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | (0.2) | (0.1)
Actuarial Loss | 2.4 | 2.7
Prior Service Cost | $ 0.7 | $ 0.9

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- Definition The change in other regulatory asset due to the amortization of the net prior service costs (credit) into net periodic pension costs. + References No definition available. + Details
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- Definition Pretax change in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan, that has not been recognized in net periodic benefit cost. + References No definition available. + Details
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- Definition he net gain (loss) previously recognized in regulatory assets that is a reclassification adjustment of other comprehensive income as a result of being recognized as a component of net periodic benefit cost for the period. + References No definition available. + Details
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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References No definition available. + Details
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