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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Storm Damage and Reliability Reserves (Details) - USD ($) $ in Millions |  | 12 Months Ended | 24 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jan. 01, 2023 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2022 | Apr. 04, 2023 | Apr. 03, 2023
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Reliability reserve, amount deferred |  | $ 63.0 | $ 191.0 |  | $ 191.0 |  |
Alabama Power |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Additional accruals authorized by state PSCs |  |  |  | $ 65.0 |  |  |
Reliability reserve, amount deferred |  | 52.0 | 166.0 |  | 166.0 |  |
Alabama Power | Weather-related damages |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Charges against storm damage reserves |  | 24.0 |  |  |  |  |
Georgia Power |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Storm damage reserves | $ 31.0 |  |  |  | 213.0 |  |
Georgia Power | Weather-related damages |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Charges against storm damage reserves |  | 82.0 |  |  |  |  |
Mississippi Power |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Reliability reserve, amount deferred |  | 11.0 | 25.0 |  | $ 25.0 | $ 11.7 | $ 8.3
Mississippi Power | Weather-related damages |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Charges against storm damage reserves |  | 0.0 |  |  |  |  |
Major storms |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Storm damage reserves |  |  | 239.0 | 286.0 |  |  |
Major storms | Alabama Power |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Additional accruals authorized by state PSCs |  |  |  | 65.0 |  |  |
Storm damage reserves |  |  | 19.0 | 75.0 |  |  |
Major storms | Georgia Power |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Storm damage reserves |  |  | 213.0 | 213.0 |  |  |
Major storms | Mississippi Power |  |  |  |  |  |  |
Liability for Catastrophe Claims [Line Items] |  |  |  |  |  |  |
Storm damage reserves |  | $ 11.7 | $ 6.9 | $ (1.8) |  |  |

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