v3.26.1
FAIR VALUE MEASUREMENTS - Significant Unobservable Inputs (Details) - USD ($)
Jun. 30, 2026
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets $ 768,000,000 $ 617,000,000
Fair value, liabilities 327,000,000 310,000,000
APPALACHIAN POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 171,000,000 82,000,000
Fair value, liabilities 12,000,000 3,000,000
INDIANA MICHIGAN POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 22,000,000 10,000,000
Fair value, liabilities 0 0
OHIO POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 0 0
Fair value, liabilities 28,000,000 33,000,000
PUBLIC SERVICE COMPANY OF OKLAHOMA    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 43,000,000 42,000,000
Fair value, liabilities 28,000,000 28,000,000
SOUTHWESTERN ELECTRIC POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 42,000,000 35,000,000
Fair value, liabilities 13,000,000 11,000,000
Energy Contracts | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 215,000,000 224,000,000
Fair value, liabilities 156,000,000 144,000,000
Energy Contracts | Level 3 | OHIO POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 0 0
Fair value, liabilities $ 28,000,000 $ 33,000,000
Energy Contracts | Level 3 | Low | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 7.89 5.65
Input/Range, liability 7.89 5.65
Energy Contracts | Level 3 | Low | OHIO POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 21.81 21.44
Input/Range, liability 21.81 21.44
Energy Contracts | Level 3 | High | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 875.00 141.75
Input/Range, liability 875.00 141.75
Energy Contracts | Level 3 | High | OHIO POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 106.13 85.92
Input/Range, liability 106.13 85.92
Energy Contracts | Level 3 | Weighted Average | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 54.52 50.61
Input/Range, liability 54.52 50.61
Energy Contracts | Level 3 | Weighted Average | OHIO POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 51.87 50.10
Input/Range, liability 51.87 50.10
FTRs | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets $ 340,000,000 $ 187,000,000
Fair value, liabilities 19,000,000 8,000,000
FTRs | Level 3 | APPALACHIAN POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 173,000,000 81,000,000
Fair value, liabilities 2,000,000 0
FTRs | Level 3 | INDIANA MICHIGAN POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 26,000,000 9,000,000
Fair value, liabilities 4,000,000 0
FTRs | Level 3 | PUBLIC SERVICE COMPANY OF OKLAHOMA    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 43,000,000 43,000,000
Fair value, liabilities 0 2,000,000
FTRs | Level 3 | SOUTHWESTERN ELECTRIC POWER COMPANY    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value, assets 42,000,000 37,000,000
Fair value, liabilities $ 0 $ 2,000,000
FTRs | Level 3 | Low | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset (76.06) (32.49)
Input/Range, liability (76.06) (32.49)
FTRs | Level 3 | Low | APPALACHIAN POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset (2.61) (0.26)
Input/Range, liability (2.61) (0.26)
FTRs | Level 3 | Low | INDIANA MICHIGAN POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset (3.47) (0.46)
Input/Range, liability (3.47) (0.46)
FTRs | Level 3 | Low | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset (20.83) (32.49)
Input/Range, liability (20.83) (32.49)
FTRs | Level 3 | Low | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset (20.83) (32.49)
Input/Range, liability (20.83) (32.49)
FTRs | Level 3 | High | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 238.16 21.68
Input/Range, liability 238.16 21.68
FTRs | Level 3 | High | APPALACHIAN POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 56.36 17.55
Input/Range, liability 56.36 17.55
FTRs | Level 3 | High | INDIANA MICHIGAN POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 42.39 21.68
Input/Range, liability 42.39 21.68
FTRs | Level 3 | High | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 1.43 8.54
Input/Range, liability 1.43 8.54
FTRs | Level 3 | High | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 1.43 8.54
Input/Range, liability 1.43 8.54
FTRs | Level 3 | Weighted Average | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 1.56 0.49
Input/Range, liability 1.56 0.49
FTRs | Level 3 | Weighted Average | APPALACHIAN POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 3.92 3.47
Input/Range, liability 3.92 3.47
FTRs | Level 3 | Weighted Average | INDIANA MICHIGAN POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset 1.06 1.60
Input/Range, liability 1.06 1.60
FTRs | Level 3 | Weighted Average | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset (7.09) (5.49)
Input/Range, liability (7.09) (5.49)
FTRs | Level 3 | Weighted Average | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Input/Range, asset (7.09) (5.49)
Input/Range, liability (7.09) (5.49)