v3.26.1
FAIR VALUE MEASUREMENTS - Debt Fair Value (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value $ 50,808 $ 47,322
Fair Value 48,075 44,930
AEP TEXAS INC.    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value 7,696 7,016
Fair Value 7,199 6,586
AEP TRANSMISSION COMPANY, LLC    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value 6,756 6,599
Fair Value 5,923 5,812
APPALACHIAN POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value 7,435 6,259
Fair Value 7,290 6,147
INDIANA MICHIGAN POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value 4,146 3,561
Fair Value 3,836 3,288
OHIO POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value 3,720 3,718
Fair Value 3,320 3,331
PUBLIC SERVICE COMPANY OF OKLAHOMA    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value 3,527 3,526
Fair Value 3,326 3,349
SOUTHWESTERN ELECTRIC POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Book Value 4,858 4,974
Fair Value $ 4,461 $ 4,603