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Regulatory Matters - Alabama Power (Details) $ in Millions |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 06, 2025 USD ($) | Oct. 29, 2025 USD ($) | Sep. 30, 2025 USD ($) MW | Dec. 31, 2025 USD ($) | Dec. 31, 2026 USD ($) | Jun. 19, 2025 USD ($) | Jun. 05, 2025 USD ($) | Dec. 31, 2024 USD ($)
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Regulatory asset balance related to storm damage |  |  | $ 856 |  |  |  |  | $ 705
ALABAMA POWER CO |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Regulatory asset balance related to storm damage |  |  | 4 |  |  |  |  |
Minimum natural disaster reserve balance, triggering establishment charge |  |  | 50 |  |  |  |  |
Natural disaster reserve authorized limit |  |  | 75 |  |  |  |  |
ALABAMA POWER CO | Subsequent Event |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Federal income tax return credit |  | $ 180 |  |  |  |  |  |
ALABAMA POWER CO | Reliability Reserve Liability |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Regulatory liability |  |  | 101 |  |  | $ 131 |  |
Decrease in accrual |  |  | 30 |  |  |  |  |
ALABAMA POWER CO | Regulatory Liability, Nuclear PTC |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Regulatory liability |  |  | $ 36 |  |  |  |  |
ALABAMA POWER CO | Jurisdictional Separation Study Order (JSS) |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Regulatory asset balance related to storm damage |  |  |  |  |  |  | $ 100 |
Regulatory asset amortization period |  |  |  |  |  |  | 10 years |
ALABAMA POWER CO | Tenaska Alabama Partners, L.P. |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Approximate nameplate capacity | MW |  |  | 855 |  |  |  |  |
Purchase price | $ 635 |  |  |  |  |  |  |
ALABAMA POWER CO | Scenario, Forecast |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Natural disaster reserve, expected recovery amount |  |  |  | $ 18 | $ 36 |  |  |

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