FAIR VALUE MEASUREMENTS - Debt Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	$ 49,554	$ 47,322
Fair Value	46,612	44,930
AEP TEXAS INC.
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	7,744	7,016
Fair Value	7,221	6,586
AEP TRANSMISSION COMPANY, LLC
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	6,613	6,599
Fair Value	5,750	5,812
APPALACHIAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	6,247	6,259
Fair Value	6,053	6,147
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	4,174	3,561
Fair Value	3,847	3,288
OHIO POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,719	3,718
Fair Value	3,289	3,331
PUBLIC SERVICE COMPANY OF OKLAHOMA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,526	3,526
Fair Value	3,307	3,349
SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	4,858	4,974
Fair Value	$ 4,449	$ 4,603