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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Costs for Affiliate Transactions (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Alabama Power | Southern Company Services, Inc. |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | $ 813 | $ 611 | $ 549
Alabama Power | Southern Natural Gas Company, LLC |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 13 | 12 | 18
Georgia Power | Southern Company Services, Inc. |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 1,197 | 857 | 762
Georgia Power | Southern Natural Gas Company, LLC |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 103 | 101 | 99
Mississippi Power | Southern Company Services, Inc. |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 130 | 113 | 115
Mississippi Power | Alabama Power | Power Pool |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 8 | 4 | 4
Southern Power | Southern Company Services, Inc. |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 93 | 86 | 86
Southern Power | Alabama Power | Power Pool |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 17 | 13 | 29
Southern Power | Southern Natural Gas Company, LLC |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 35 | 34 | 37
Southern Company Gas | Southern Company Services, Inc. |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | 290 | 261 | 262
Southern Company Gas | Southern Natural Gas Company, LLC |  |  |
Related Party Transaction [Line Items] |  |  |
Costs for services | $ 28 | $ 28 | $ 27

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