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PROPERTY, PLANT, AND EQUIPMENT - Additional Information (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Property, Plant and Equipment [Line Items] |  |  |
Regulatory asset amortization period | 4 years |  |
Deferred Cloud Implementation Costs |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Amortization | $ 46 | $ 29 | $ 0
Alabama Power | Deferred Cloud Implementation Costs |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Amortization | 11 | 8 | 0
Georgia Power | Deferred Cloud Implementation Costs |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Amortization | 19 | 12 | 0
Southern Company Gas | Deferred Cloud Implementation Costs |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Amortization | 8 | 0 | 0
SOUTHERN POWER CO | Deferred Cloud Implementation Costs |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Amortization | 0 | 0 | 0
Mississippi Power | Deferred Cloud Implementation Costs |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Amortization | $ 0 | $ 0 | $ 0
Plant Farley | Alabama Power | Nuclear Outage |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory asset amortization period | 18 months |  |
Plant Hatch Units 1 and 2 | Georgia Power | Nuclear Outage | Maximum |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory asset amortization period | 24 months |  |
Plant Vogtle Nuclear Units One , Two, and Three | Georgia Power | Nuclear Outage |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory asset amortization period | 18 months |  |

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