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FAIR VALUE MEASUREMENTS - Changes in Fair Value (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] |  |  |
Beginning balance | $ 139.4 | $ 160.4 | $ 103.1
Realized gain (loss) included in net income (or changes in net assets) | $ 90.3 | $ 52.1 | $ 69.5
Fair value, net derivative asset (liability), recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income | Total Revenues | Total Revenues | Total Revenues
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date | $ 14.8 | $ 71.1 | $ (34.9)
Fair value, net derivative asset (liability), recurring basis, still held, unrealized gain (loss), statement of income or comprehensive income | Total Revenues | Total Revenues | Total Revenues
Realized and unrealized gains (losses) included in other comprehensive income | $ 3.9 | $ (17.4) | $ 9.6
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] | Cash Flow Hedges, Net of Tax | Cash Flow Hedges, Net of Tax | Cash Flow Hedges, Net of Tax
Settlements | $ (167.6) | $ (172.2) | $ (154.6)
Transfers into Level 3 | 6.8 | (6.1) | 1.7
Transfers out of Level 3 | (6.4) | 3.8 | 0.1
Changes in fair value allocated to regulated jurisdictions | 84.4 | 47.7 | 165.9
Ending balance | 165.6 | 139.4 | 160.4
APPALACHIAN POWER COMPANY |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] |  |  |
Beginning balance | 22.4 | 69.1 | 41.7
Realized gain (loss) included in net income (or changes in net assets) | 24.1 | (11.7) | 3.0
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date | 0.0 | 0.0 | 0.0
Realized and unrealized gains (losses) included in other comprehensive income | 0.0 | 0.0 | 0.0
Settlements | (46.5) | (57.3) | (44.7)
Transfers into Level 3 | 0.0 | 0.0 | 0.0
Transfers out of Level 3 | 0.0 | 0.0 | 0.0
Changes in fair value allocated to regulated jurisdictions | 35.2 | 22.3 | 69.1
Ending balance | 35.2 | 22.4 | 69.1
INDIANA MICHIGAN POWER COMPANY |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] |  |  |
Beginning balance | 2.8 | 4.6 | (0.7)
Realized gain (loss) included in net income (or changes in net assets) | 7.3 | 4.2 | 3.7
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date | 0.0 | 0.0 | 0.0
Realized and unrealized gains (losses) included in other comprehensive income | 0.0 | 0.0 | 0.0
Settlements | (10.0) | (8.8) | (3.0)
Transfers into Level 3 | 0.0 | 0.0 | 0.0
Transfers out of Level 3 | 0.0 | 0.0 | 0.0
Changes in fair value allocated to regulated jurisdictions | 6.3 | 2.8 | 4.6
Ending balance | 6.4 | 2.8 | 4.6
OHIO POWER COMPANY |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] |  |  |
Beginning balance | (50.6) | (40.0) | (92.5)
Realized gain (loss) included in net income (or changes in net assets) | (1.1) | (3.6) | 6.5
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date | 0.0 | 0.0 | 0.0
Realized and unrealized gains (losses) included in other comprehensive income | 0.0 | 0.0 | 0.0
Settlements | 7.9 | 5.6 | 0.3
Transfers into Level 3 | 0.0 | 0.0 | 0.0
Transfers out of Level 3 | 0.0 | 0.0 | 0.0
Changes in fair value allocated to regulated jurisdictions | (3.7) | (12.6) | 45.7
Ending balance | (47.5) | (50.6) | (40.0)
PUBLIC SERVICE COMPANY OF OKLAHOMA |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] |  |  |
Beginning balance | 18.6 | 23.7 | 12.1
Realized gain (loss) included in net income (or changes in net assets) | 26.2 | 29.8 | 24.2
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date | 0.0 | 0.0 | 0.0
Realized and unrealized gains (losses) included in other comprehensive income | 0.0 | 0.0 | 0.0
Settlements | (44.8) | (53.4) | (36.3)
Transfers into Level 3 | 0.0 | 0.0 | 0.0
Transfers out of Level 3 | 0.0 | 0.0 | 0.0
Changes in fair value allocated to regulated jurisdictions | 20.0 | 18.5 | 23.7
Ending balance | 20.0 | 18.6 | 23.7
SOUTHWESTERN ELECTRIC POWER COMPANY |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] |  |  |
Beginning balance | 11.1 | 14.2 | 10.9
Realized gain (loss) included in net income (or changes in net assets) | 23.6 | 20.0 | 35.8
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date | 0.0 | 0.0 | 0.0
Realized and unrealized gains (losses) included in other comprehensive income | 0.0 | 0.0 | 0.0
Settlements | (36.0) | (34.2) | (45.0)
Transfers into Level 3 | 0.0 | 0.0 | 0.0
Transfers out of Level 3 | 0.5 | 0.0 | 6.9
Changes in fair value allocated to regulated jurisdictions | 18.3 | 11.1 | 5.6
Ending balance | $ 17.5 | $ 11.1 | $ 14.2

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