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RETIREMENT BENEFITS - Regulatory Assets (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | $ 6,523 | $ 5,833
Regulatory asset | 66 | 216
Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 2,720 | 2,340
Regulatory asset | 76 | 97
Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 5,090 | 4,663
Regulatory asset |  | 83
Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 90 | 4
Regulatory asset | 44 | 36
Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | (2,225) | (1,891)
Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 2,913 | 2,371
Pension plans | Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 821 | 679
Pension plans | Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 1,051 | 887
Pension plans | Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 152 | 123
Pension plans | Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 143 | 111
Regulatory asset | 173 | 190
Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 203 | 136
Other Postretirement Benefits Plan | Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 48 | 21
Other Postretirement Benefits Plan | Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 74 | 39
Other Postretirement Benefits Plan | Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 10 | (9)
Other Postretirement Benefits Plan | Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 68 | 58
Regulatory asset | 24 | 32
Prior Service Cost | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 9 | 10
Prior Service Cost | Pension plans | Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 4 | 4
Prior Service Cost | Pension plans | Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 6 | 7
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 | (7) | (9)
Prior Service Cost | Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 13 | 14
Prior Service Cost | Other Postretirement Benefits Plan | Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 4 | 4
Prior Service Cost | Other Postretirement Benefits Plan | Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 5 | 6
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 | 1
Net Actuarial Gain (Loss) | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 2,904 | 2,361
Net Actuarial Gain (Loss) | Pension plans | Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 817 | 675
Net Actuarial Gain (Loss) | Pension plans | Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 1,045 | 880
Net Actuarial Gain (Loss) | Pension plans | Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 151 | 122
Net Actuarial Gain (Loss) | Pension plans | Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 100 | 66
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 216 | 150
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 52 | 25
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 79 | 45
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 11 | 10
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net regulatory assets | 64 | 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 | 50 | 54
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 | $ (4) | $ 5

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