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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Storm Damage and Reliability Reserves (Details) - USD ($) $ in Millions |  | 1 Months Ended | 12 Months Ended | 24 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jan. 01, 2023 | Sep. 30, 2024 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2022 | Apr. 11, 2024 | Apr. 30, 2023 | Mar. 31, 2023
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Balance at December 31, 2023 | $ 216.0 |  | $ 66.0 | $ 216.0 |  |  |  |  |
Balance at December 31, 2024 |  |  |  | 66.0 | $ 216.0 | $ 216.0 |  |  |
Balance at December 31, 2024 |  |  | (705.0) |  |  |  |  |  |
Reliability reserve, amount deferred |  |  | 84.0 | 63.0 | 191.0 | 191.0 |  |  |
Major storms |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Storm damage reserves |  |  |  |  | 239.0 |  |  |  |
Accrual |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Accrual |  |  | 79.0 | 61.0 |  |  |  |  |
Weather-related damages |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Weather-related damages |  |  | (850.0) | (211.0) |  |  |  |  |
Alabama Power |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Balance at December 31, 2023 | 97.0 |  | 76.0 | 97.0 |  |  |  |  |
Balance at December 31, 2024 |  |  | 70.0 | 76.0 | 97.0 | 97.0 |  |  |
Reliability reserve, amount deferred |  |  | 63.0 | 52.0 | 166.0 | 166.0 |  |  |
Alabama Power | Major storms |  |  |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |  |  |
Additional accruals authorized by state PSCs |  |  | 21.0 |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Storm damage reserves |  |  |  |  | 19.0 |  |  |  |
Alabama Power | Accrual |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Accrual |  |  | 34.0 | 18.0 |  |  |  |  |
Alabama Power | Weather-related damages |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Weather-related damages |  |  | (40.0) | (39.0) |  |  |  |  |
Charges against storm damage reserves |  |  | 24.0 |  |  |  |  |  |
Georgia Power |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Balance at December 31, 2023 | 83.0 |  |  | 83.0 |  |  |  |  |
Balance at December 31, 2024 |  |  |  |  | 83.0 | 83.0 |  |  |
Balance at December 31, 2024 |  |  | (827.0) | (54.0) |  |  |  |  |
Storm damage reserves | 31.0 |  |  |  |  | 213.0 |  |  |
Georgia Power | Major storms |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Weather-related damages |  | $ (870.0) |  |  |  |  |  |  |
Balance at December 31, 2024 |  |  | 750.0 |  |  |  |  |  |
Storm damage reserves |  |  |  |  | 213.0 |  |  |  |
Georgia Power | Accrual |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Accrual |  |  | 31.0 | 31.0 |  |  |  |  |
Georgia Power | Weather-related damages |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Weather-related damages |  |  | (804.0) | (168.0) |  |  |  |  |
Charges against storm damage reserves |  |  | 82.0 |  |  |  |  |  |
Mississippi Power |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Balance at December 31, 2023 | $ 36.0 |  | 44.0 | 36.0 |  |  |  |  |
Balance at December 31, 2024 |  |  | 52.0 | 44.0 | 36.0 | 36.0 |  |  |
Reliability reserve, amount deferred |  |  | 21.0 | 11.0 | 25.0 | $ 25.0 | $ 12.6 | $ 11.7 | $ 8.3
Mississippi Power | Major storms |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Storm damage reserves |  |  | 12.6 | 11.7 | $ 6.9 |  |  |  |
Mississippi Power | Accrual |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Accrual |  |  | 14.0 | 12.0 |  |  |  |  |
Mississippi Power | Weather-related damages |  |  |  |  |  |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |  |  |  |  |  |
Weather-related damages |  |  | (6.0) | $ (4.0) |  |  |  |  |
Charges against storm damage reserves |  |  | $ 0.0 |  |  |  |  |  |

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