FAIR VALUE MEASUREMENTS - Significant Unobservable Inputs (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	$ 499,500,000	$ 538,700,000
Fair value, liabilities	324,400,000	471,400,000
APPALACHIAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	37,100,000	22,400,000
Fair value, liabilities	2,200,000	22,500,000
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	18,400,000	39,600,000
Fair value, liabilities	700,000	2,000,000.0
OHIO POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	0	0
Fair value, liabilities	47,500,000	50,700,000
PUBLIC SERVICE COMPANY OF OKLAHOMA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	22,000,000.0	19,000,000.0
Fair value, liabilities	5,800,000	29,900,000
SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	18,100,000	11,600,000
Fair value, liabilities	2,300,000	15,600,000
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	313,500,000	294,100,000
Fair value, liabilities	147,900,000	154,700,000
Energy Contracts | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	221,200,000	225,500,000
Fair value, liabilities	144,600,000	144,900,000
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	$ 47,500,000	$ 50,600,000
Energy Contracts | Level 3 | Low | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	2.75	5.21
Input/Range	2.75	5.21
Energy Contracts | Level 3 | Low | OHIO POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	14.53	22.92
Input/Range	14.53	22.92
Energy Contracts | Level 3 | High | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	149.30	153.77
Input/Range	149.30	153.77
Energy Contracts | Level 3 | High | OHIO POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	72.40	67.53
Input/Range	72.40	67.53
Energy Contracts | Level 3 | Weighted Average | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	49.34	45.05
Input/Range	49.34	45.05
Energy Contracts | Level 3 | Weighted Average | OHIO POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	42.44	42.85
Input/Range	42.44	42.85
FTRs | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	$ 92,300,000	$ 68,600,000
Fair value, liabilities	3,300,000	9,300,000
FTRs | Level 3 | APPALACHIAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	35,200,000	23,500,000
Fair value, liabilities	0	1,100,000
FTRs | Level 3 | INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	6,900,000	4,500,000
Fair value, liabilities	500,000	1,700,000
FTRs | Level 3 | PUBLIC SERVICE COMPANY OF OKLAHOMA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	20,800,000	19,700,000
Fair value, liabilities	800,000	1,100,000
FTRs | Level 3 | SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	18,100,000	12,000,000.0
Fair value, liabilities	$ 600,000	$ 400,000
FTRs | Level 3 | Low | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	(29.48)	(25.45)
Input/Range	(29.48)	(25.45)
FTRs | Level 3 | Low | APPALACHIAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	(0.25)	(1.04)
Input/Range	(0.25)	(1.04)
FTRs | Level 3 | Low | INDIANA MICHIGAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	(4.07)	(1.48)
Input/Range	(4.07)	(1.48)
FTRs | Level 3 | Low | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	(29.48)	(25.45)
Input/Range	(29.48)	(25.45)
FTRs | Level 3 | Low | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	(29.48)	(25.45)
Input/Range	(29.48)	(25.45)
FTRs | Level 3 | High | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	19.70	17.07
Input/Range	19.70	17.07
FTRs | Level 3 | High | APPALACHIAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	9.32	6.45
Input/Range	9.32	6.45
FTRs | Level 3 | High | INDIANA MICHIGAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	9.32	8.40
Input/Range	9.32	8.40
FTRs | Level 3 | High | PUBLIC SERVICE COMPANY OF OKLAHOMA | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	10.54	4.80
Input/Range	10.54	4.80
FTRs | Level 3 | High | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	10.54	4.80
Input/Range	10.54	4.80
FTRs | Level 3 | Weighted Average | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	0.24	0
Input/Range	0.24	0
FTRs | Level 3 | Weighted Average | APPALACHIAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	1.56	1.36
Input/Range	1.56	1.36
FTRs | Level 3 | Weighted Average | INDIANA MICHIGAN POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	1.34	0.85
Input/Range	1.34	0.85
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	(3.88)	(4.33)
Input/Range	(3.88)	(4.33)
FTRs | Level 3 | Weighted Average | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range	(3.88)	(4.33)
Input/Range	(3.88)	(4.33)
Natural Gas (MMBtus) | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets		$ 0
Fair value, liabilities		500,000
Natural Gas (MMBtus) | Level 3 | SOUTHWESTERN ELECTRIC POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets		0
Fair value, liabilities		$ 500,000
Natural Gas (MMBtus) | Level 3 | Low | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range		3.11
Input/Range		3.11
Natural Gas (MMBtus) | Level 3 | Low | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range		3.11
Input/Range		3.11
Natural Gas (MMBtus) | Level 3 | High | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range		3.11
Input/Range		3.11
Natural Gas (MMBtus) | Level 3 | High | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range		3.11
Input/Range		3.11
Natural Gas (MMBtus) | Level 3 | Weighted Average | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range		3.11
Input/Range		3.11
Natural Gas (MMBtus) | Level 3 | Weighted Average | SOUTHWESTERN ELECTRIC POWER COMPANY | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range		3.11
Input/Range		3.11