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Introduction - Storm Damage Reserves and Depreciation (Details) - USD ($) $ in Millions |  | 1 Months Ended | 9 Months Ended
--- | --- | --- | ---
Apr. 01, 2025 | Jun. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Balance at December 31, 2024 |  |  |  | $ (705)
Balance at September 30, 2025 |  |  | $ (705) | (856)
Accrued Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Accrual |  |  |  | 58
Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Weather-related damages |  |  |  | (209)
ALABAMA POWER CO |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Balance at December 31, 2024 |  |  |  | 70
Balance at September 30, 2025 |  |  |  | (4)
Balance at September 30, 2025 |  |  | 70 |
Amount awarded |  |  | 7 |
Asset retirement obligation, period decrease |  | $ 257 |  |
ALABAMA POWER CO | Accrued Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Accrual |  |  |  | 23
ALABAMA POWER CO | Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Weather-related damages |  |  |  | (97)
GEORGIA POWER CO |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Balance at December 31, 2024 |  |  |  | (827)
Balance at September 30, 2025 |  |  | (827) | (907)
GEORGIA POWER CO | Accrued Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Accrual |  |  |  | 24
GEORGIA POWER CO | Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Weather-related damages |  |  |  | (104)
MISSISSIPPI POWER CO |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Balance at December 31, 2024 |  |  |  | 52
Balance at September 30, 2025 |  |  | $ 52 | 55
Approved rate increase (decrease) | $ 8 |  |  |
Asset retirement obligation, period decrease |  | $ 13 |  |
MISSISSIPPI POWER CO | Accrued Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Accrual |  |  |  | 11
MISSISSIPPI POWER CO | Storm Reserve |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Weather-related damages |  |  |  | $ (8)

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