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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Total AFUDC and Interest Capitalized (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Capitalized Contract Cost [Line Items] |  |  |
Total AFUDC and interest capitalized | $ 339 | $ 400 | $ 327
Alabama Power |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Total AFUDC and interest capitalized | 76 | 109 | 90
Georgia Power |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Total AFUDC and interest capitalized | 209 | 251 | 213
Southern Power |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Total AFUDC and interest capitalized | 7 | 3 | 0
Southern Company Gas |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Total AFUDC and interest capitalized | $ 47 | $ 37 | $ 24

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