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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)

X
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