FAIR VALUE MEASUREMENTS - Significant Unobservable Inputs (Details) - USD ($)	Dec. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	$ 617,000,000	$ 499,000,000
Fair value, liabilities	310,000,000	324,000,000
APPALACHIAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	82,000,000	37,000,000
Fair value, liabilities	3,000,000	2,000,000
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	10,000,000	18,000,000
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	33,000,000	47,000,000
PUBLIC SERVICE COMPANY OF OKLAHOMA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	42,000,000	22,000,000
Fair value, liabilities	28,000,000	6,000,000
SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	35,000,000	18,000,000
Fair value, liabilities	11,000,000	2,000,000
Energy Contracts | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	224,000,000	221,000,000
Fair value, liabilities	144,000,000	145,000,000
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	$ 33,000,000	$ 47,000,000
Energy Contracts | Level 3 | Low | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	5.65	2.75
Derivative liability, measurement input	5.65	2.75
Energy Contracts | Level 3 | Low | OHIO POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	21.44	14.53
Derivative liability, measurement input	21.44	14.53
Energy Contracts | Level 3 | High | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	141.75	149.30
Derivative liability, measurement input	141.75	149.30
Energy Contracts | Level 3 | High | OHIO POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	85.92	72.40
Derivative liability, measurement input	85.92	72.40
Energy Contracts | Level 3 | Weighted Average | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	50.61	49.34
Derivative liability, measurement input	50.61	49.34
Energy Contracts | Level 3 | Weighted Average | OHIO POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	50.10	42.44
Derivative liability, measurement input	50.10	42.44
FTRs | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	$ 187,000,000	$ 93,000,000
Fair value, liabilities	8,000,000	3,000,000
FTRs | Level 3 | APPALACHIAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	81,000,000	35,000,000
Fair value, liabilities	0	0
FTRs | Level 3 | INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	9,000,000	7,000,000
Fair value, liabilities	0	1,000,000
FTRs | Level 3 | PUBLIC SERVICE COMPANY OF OKLAHOMA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	43,000,000	21,000,000
Fair value, liabilities	2,000,000	1,000,000
FTRs | Level 3 | SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	37,000,000	18,000,000
Fair value, liabilities	$ 2,000,000	$ 1,000,000
FTRs | Level 3 | Low | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	(32.49)	(29.48)
Derivative liability, measurement input	(32.49)	(29.48)
FTRs | Level 3 | Low | APPALACHIAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	(0.26)	(0.25)
Derivative liability, measurement input	(0.26)	(0.25)
FTRs | Level 3 | Low | INDIANA MICHIGAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	(0.46)	(4.07)
Derivative liability, measurement input	(0.46)	(4.07)
FTRs | Level 3 | Low | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	(32.49)	(29.48)
Derivative liability, measurement input	(32.49)	(29.48)
FTRs | Level 3 | Low | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	(32.49)	(29.48)
Derivative liability, measurement input	(32.49)	(29.48)
FTRs | Level 3 | High | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	21.68	19.70
Derivative liability, measurement input	21.68	19.70
FTRs | Level 3 | High | APPALACHIAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	17.55	9.32
Derivative liability, measurement input	17.55	9.32
FTRs | Level 3 | High | INDIANA MICHIGAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	21.68	9.32
Derivative liability, measurement input	21.68	9.32
FTRs | Level 3 | High | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	8.54	10.54
Derivative liability, measurement input	8.54	10.54
FTRs | Level 3 | High | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	8.54	10.54
Derivative liability, measurement input	8.54	10.54
FTRs | Level 3 | Weighted Average | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	0.49	0.24
Derivative liability, measurement input	0.49	0.24
FTRs | Level 3 | Weighted Average | APPALACHIAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	3.47	1.56
Derivative liability, measurement input	3.47	1.56
FTRs | Level 3 | Weighted Average | INDIANA MICHIGAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	1.60	1.34
Derivative liability, measurement input	1.60	1.34
FTRs | Level 3 | Weighted Average | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	(5.49)	(3.88)
Derivative liability, measurement input	(5.49)	(3.88)
FTRs | Level 3 | Weighted Average | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative asset, measurement input	(5.49)	(3.88)
Derivative liability, measurement input	(5.49)	(3.88)