PROPERTY, PLANT AND EQUIPMENT - Allowance for Equity Funds and Borrowed Funds Used During Construction (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	$ 245	$ 211	$ 175
Borrowed funds used during construction	154	130	117
AEP TEXAS INC.
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	53	46	28
Borrowed funds used during construction	28	31	23
AEP TRANSMISSION COMPANY, LLC
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	93	89	83
Borrowed funds used during construction	37	34	31
APPALACHIAN POWER COMPANY
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	17	16	12
Borrowed funds used during construction	10	11	14
INDIANA MICHIGAN POWER COMPANY
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	18	13	11
Borrowed funds used during construction	10	9	8
OHIO POWER COMPANY
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	25	23	17
Borrowed funds used during construction	13	13	14
PUBLIC SERVICE COMPANY OF OKLAHOMA
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	11	7	8
Borrowed funds used during construction	9	10	5
SOUTHWESTERN ELECTRIC POWER COMPANY
Property, Plant and Equipment [Line Items]
Allowance for equity funds used during construction	23	14	11
Borrowed funds used during construction	$ 13	$ 15	$ 10