FAIR VALUE MEASUREMENTS - Changes in Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 166	$ 139	$ 160
Realized gain (loss) included in net income (or changes in net assets)	$ 157	$ 90	$ 52
Fair value, net derivative asset (liability), recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income	Net Income	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	$ 19	$ 15	$ 71
Fair value, net derivative asset (liability), recurring basis, still held, unrealized gain (loss), statement of income or comprehensive income	Net Income	Total Revenues	Total Revenues
Realized and unrealized gains (losses) included in other comprehensive income	$ 16	$ 4	$ (17)
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax
Settlements	$ (286)	$ (168)	$ (172)
Transfers into Level 3	1	7	(6)
Transfers out of Level 3	(2)	(6)	4
Changes in fair value allocated to regulated jurisdictions	188	85	47
Ending balance	259	166	139
APPALACHIAN POWER COMPANY
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	35	22	69
Realized gain (loss) included in net income (or changes in net assets)	50	24	(12)
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date	0	0	0
Realized and unrealized gains (losses) included in other comprehensive income	0	0	0
Settlements	(85)	(46)	(57)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Changes in fair value allocated to regulated jurisdictions	81	35	22
Ending balance	81	35	22
INDIANA MICHIGAN POWER COMPANY
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	6	3	5
Realized gain (loss) included in net income (or changes in net assets)	13	7	4
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date	0	0	0
Realized and unrealized gains (losses) included in other comprehensive income	0	0	0
Settlements	(19)	(10)	(9)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Changes in fair value allocated to regulated jurisdictions	9	6	3
Ending balance	9	6	3
OHIO POWER COMPANY
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	(47)	(51)	(40)
Realized gain (loss) included in net income (or changes in net assets)	0	(1)	(4)
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date	0	0	0
Realized and unrealized gains (losses) included in other comprehensive income	0	0	0
Settlements	7	8	6
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Changes in fair value allocated to regulated jurisdictions	7	(3)	(13)
Ending balance	(33)	(47)	(51)
PUBLIC SERVICE COMPANY OF OKLAHOMA
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	20	19	24
Realized gain (loss) included in net income (or changes in net assets)	38	26	30
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date	0	0	0
Realized and unrealized gains (losses) included in other comprehensive income	0	0	0
Settlements	(58)	(45)	(53)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Changes in fair value allocated to regulated jurisdictions	41	20	18
Ending balance	41	20	19
SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	17	11	14
Realized gain (loss) included in net income (or changes in net assets)	43	24	20
Unrealized gain (loss) included in net income (or changes in net assets) relating to assets still held at the reporting date	0	0	0
Realized and unrealized gains (losses) included in other comprehensive income	0	0	0
Settlements	(59)	(36)	(34)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Changes in fair value allocated to regulated jurisdictions	34	18	11
Ending balance	$ 35	$ 17	$ 11