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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Affiliate Transactions (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Southern Nuclear Operating Company, Inc. | Alabama Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | $ 260 | $ 251 | $ 267
Southern Nuclear Operating Company, Inc. | Georgia Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 835 | 899 | 895
Southern Power | Georgia Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 203 | 143 | 151
PowerSecure | Southern Company Gas | US General Services Administration |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 13 | 29 | 10
Contract amount |  |  | 74
Southern Company Services, Inc. | Alabama Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 813 | 611 | 549
Southern Company Services, Inc. | Georgia Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 1,197 | 857 | 762
Southern Company Services, Inc. | Southern Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 93 | 86 | 86
Southern Company Services, Inc. | Southern Company Gas |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 290 | 261 | 262
Southern Company Services, Inc. | Mississippi Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 130 | 113 | 115
Non-Fuel Expense | Mississippi Power | Alabama Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 7 | 5 | 6
Purchased Power from Affiliates | Southern Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 149 | 145 | 154
Operating Lease PPA | Southern Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 121 | 116 | 116
Operating Lease PPA | Mississippi Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 60 |  |
Electric Transmission | Southern Company Services, Inc. | Southern Power |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | $ 25 | $ 33 | $ 39

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