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RATE MATTERS - Dolet Hills Power Station and Related Fuel Operations (Details) - Dolet Hills Power Station and Related Fuel Operations - SWEPCo - USD ($) $ in Millions | 1 Months Ended |  |
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Apr. 30, 2024 | Feb. 29, 2024 | Sep. 30, 2023 | Aug. 31, 2022 | Mar. 31, 2021 | Sep. 30, 2025 | Dec. 31, 2021
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Fuel supply provided, percentage |  |  |  |  |  |  | 100.00%
Regulatory asset, net investment |  |  |  |  |  | $ 67 |
Regulatory asset, net under-recovered fuel costs |  |  |  |  |  | 23 |
Louisiana |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Regulatory asset, recovery of fuel costs |  |  |  |  | $ 20 |  |
Regulatory asset, recovery of fuel costs, deferred |  |  |  |  | 35 |  |
Regulatory asset, fuel disallowance |  |  |  | $ 55 |  |  |
Regulatory asset, fuel disallowance, deferral |  |  |  | $ 35 |  |  |
Regulatory asset, refund to customer period |  |  |  | 5 years |  |  |
Regulatory asset, refund to customer, proposed amount |  | $ 55 |  |  |  |  |
Regulatory asset, deferral, denial of recovery |  | $ 35 |  |  |  |  |
Disallowance of fuel costs | $ 11 |  |  |  |  |  |
Regulatory asset |  |  |  |  |  | $ 24 |
Approved Recovery Period |  |  |  |  |  | 3 years |
Arkansas |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Regulatory asset, recovery of fuel costs |  |  |  |  | $ 20 |  |
Regulatory asset, recovery of fuel costs, period |  |  |  |  | 5 years |  |
Texas |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Regulatory asset, recovery of fuel costs |  |  | $ 48 |  |  |  |

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