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RETIREMENT BENEFITS - Regulatory Assets (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | $ 7,041 | $ 6,523 |
Regulatory asset |  | 66 | $ 216
Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 2,356 | 2,720 |
Regulatory asset | 70 | 76 | 97
Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 6,139 | 5,090 |
Regulatory asset |  |  | 83
Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 59 | 90 |
Regulatory asset | 52 | 44 | $ 36
Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | (2,252) | (2,225) |
Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 2,658 | 2,913 |
Pension plans | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 741 | 821 |
Pension plans | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 973 | 1,051 |
Pension plans | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 144 | 152 |
Pension plans | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 126 | 143 |
Regulatory asset | 155 | 173 |
Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 189 | 203 |
Other Postretirement Benefits Plan | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 45 | 48 |
Other Postretirement Benefits Plan | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 64 | 74 |
Other Postretirement Benefits Plan | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 9 | (10) |
Other Postretirement Benefits Plan | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 84 | 68 |
Regulatory asset | 16 | 24 |
Prior Service Cost | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 8 | 9 |
Prior Service Cost | Pension plans | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 3 | 4 |
Prior Service Cost | Pension plans | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 5 | 6 |
Prior Service Cost | Pension plans | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 1 | 1 |
Prior Service Cost | Pension plans | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | (4) | (7) |
Prior Service Cost | Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 11 | 13 |
Prior Service Cost | Other Postretirement Benefits Plan | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 3 | 4 |
Prior Service Cost | Other Postretirement Benefits Plan | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 4 | 5 |
Prior Service Cost | Other Postretirement Benefits Plan | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 1 | 1 |
Prior Service Cost | Other Postretirement Benefits Plan | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Net Actuarial Gain (Loss) | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 2,650 | 2,904 |
Net Actuarial Gain (Loss) | Pension plans | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 738 | 817 |
Net Actuarial Gain (Loss) | Pension plans | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 968 | 1,045 |
Net Actuarial Gain (Loss) | Pension plans | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 143 | 151 |
Net Actuarial Gain (Loss) | Pension plans | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 91 | 100 |
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 200 | 216 |
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 48 | 52 |
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 68 | 79 |
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 10 | 11 |
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 71 | 64 |
Regulatory Amortization | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Pension plans | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Pension plans | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Pension plans | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Pension plans | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 39 | 50 |
Regulatory Amortization | Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Other Postretirement Benefits Plan | Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Other Postretirement Benefits Plan | Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Other Postretirement Benefits Plan | Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | 0 | 0 |
Regulatory Amortization | Other Postretirement Benefits Plan | Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net regulatory assets | $ (13) | $ (4) |

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