FAIR VALUE MEASUREMENTS - Significant Unobservable Inputs (Details) - USD ($)	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	$ 672,500,000	$ 499,500,000
Fair value, liabilities	309,600,000	324,400,000
APCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	94,100,000	37,100,000
Fair value, liabilities	2,700,000	2,200,000
I&M
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	10,900,000	18,400,000
Fair value, liabilities	1,000,000.0	700,000
OPCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	0	0
Fair value, liabilities	44,300,000	47,500,000
PSO
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	68,100,000	22,000,000.0
Fair value, liabilities	17,300,000	5,800,000
SWEPCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	57,800,000	18,100,000
Fair value, liabilities	5,400,000	2,300,000
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	476,700,000	313,500,000
Fair value, liabilities	149,600,000	147,900,000
Energy Contracts | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	225,700,000	221,200,000
Fair value, liabilities	141,200,000	144,600,000
Energy Contracts | Level 3 | OPCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	0	0
Fair value, liabilities	$ 44,300,000	$ 47,500,000
Energy Contracts | Level 3 | Low | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	2.24	2.75
Input/Range, liability	2.24	2.75
Energy Contracts | Level 3 | Low | OPCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	13.67	14.53
Input/Range, liability	13.67	14.53
Energy Contracts | Level 3 | High | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	144.31	149.30
Input/Range, liability	144.31	149.30
Energy Contracts | Level 3 | High | OPCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	78.67	72.40
Input/Range, liability	78.67	72.40
Energy Contracts | Level 3 | Weighted Average | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	49.61	49.34
Input/Range, liability	49.61	49.34
Energy Contracts | Level 3 | Weighted Average | OPCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	43.36	42.44
Input/Range, liability	43.36	42.44
FTRs | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	$ 251,000,000.0	$ 92,300,000
Fair value, liabilities	8,400,000	3,300,000
FTRs | Level 3 | APCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	91,400,000	35,200,000
Fair value, liabilities	100,000	0
FTRs | Level 3 | I&M
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	11,300,000	6,900,000
Fair value, liabilities	400,000	500,000
FTRs | Level 3 | PSO
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	68,300,000	20,800,000
Fair value, liabilities	3,000,000.0	800,000
FTRs | Level 3 | SWEPCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, assets	59,400,000	18,100,000
Fair value, liabilities	$ 2,800,000	$ 600,000
FTRs | Level 3 | Low | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(33.94)	(29.48)
Input/Range, liability	(33.94)	(29.48)
FTRs | Level 3 | Low | APCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(1.01)	(0.25)
Input/Range, liability	(1.01)	(0.25)
FTRs | Level 3 | Low | I&M | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(0.16)	(4.07)
Input/Range, liability	(0.16)	(4.07)
FTRs | Level 3 | Low | PSO | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(33.94)	(29.48)
Input/Range, liability	(33.94)	(29.48)
FTRs | Level 3 | Low | SWEPCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(33.94)	(29.48)
Input/Range, liability	(33.94)	(29.48)
FTRs | Level 3 | High | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	45.81	19.70
Input/Range, liability	45.81	19.70
FTRs | Level 3 | High | APCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	12.36	9.32
Input/Range, liability	12.36	9.32
FTRs | Level 3 | High | I&M | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	14.70	9.32
Input/Range, liability	14.70	9.32
FTRs | Level 3 | High | PSO | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	9.23	10.54
Input/Range, liability	9.23	10.54
FTRs | Level 3 | High | SWEPCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	9.23	10.54
Input/Range, liability	9.23	10.54
FTRs | Level 3 | Weighted Average | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(0.06)	0.24
Input/Range, liability	(0.06)	0.24
FTRs | Level 3 | Weighted Average | APCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	2.44	1.56
Input/Range, liability	2.44	1.56
FTRs | Level 3 | Weighted Average | I&M | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	1.28	1.34
Input/Range, liability	1.28	1.34
FTRs | Level 3 | Weighted Average | PSO | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(6.03)	(3.88)
Input/Range, liability	(6.03)	(3.88)
FTRs | Level 3 | Weighted Average | SWEPCo | Forward Market Price
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Input/Range, asset	(6.03)	(3.88)
Input/Range, liability	(6.03)	(3.88)