INCOME TAXES - Income Taxes Paid (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	$ 0	$ 7
Transfer Credits	(14)	(17)
Total Cash Paid/(Received)	(14)	(10)
AEP TEXAS INC.
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	(10)	0
Transfer Credits	0	0
Total Cash Paid/(Received)	(10)	0
AEP TRANSMISSION COMPANY, LLC
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	2	0
Transfer Credits	0	0
Total Cash Paid/(Received)	2	0
APPALACHIAN POWER COMPANY
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	(30)	0
Transfer Credits	(4)	0
Total Cash Paid/(Received)	(34)	0
INDIANA MICHIGAN POWER COMPANY
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	22	5
Transfer Credits	0	0
Total Cash Paid/(Received)	22	5
OHIO POWER COMPANY
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	(40)	0
Transfer Credits	0	0
Total Cash Paid/(Received)	(40)	0
PUBLIC SERVICE COMPANY OF OKLAHOMA
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	31	0
Transfer Credits	(6)	(9)
Total Cash Paid/(Received)	25	(9)
SOUTHWESTERN ELECTRIC POWER COMPANY
Income Tax Paid, by Individual Jurisdiction [Line Items]
Income Taxes Paid/(Received)	31	0
Transfer Credits	(3)	(9)
Total Cash Paid/(Received)	$ 28	$ (9)