FAIR VALUE MEASUREMENTS - Debt Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	$ 47,322	$ 42,643
Fair Value	44,930	38,965
AEP TEXAS INC.
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	7,016	6,442
Fair Value	6,586	5,831
AEP TRANSMISSION COMPANY, LLC
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	6,599	5,768
Fair Value	5,812	4,853
APPALACHIAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	6,259	5,661
Fair Value	6,147	5,346
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,561	3,494
Fair Value	3,288	3,154
OHIO POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,718	3,716
Fair Value	3,331	3,203
PUBLIC SERVICE COMPANY OF OKLAHOMA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,526	2,856
Fair Value	3,349	2,562
SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	4,974	3,981
Fair Value	$ 4,603	$ 3,432