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