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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | --- | --- | ---
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |  |
Cash and cash equivalents | $ 748 | $ 1,917 |  |
Restricted cash: |  |  |  |
Total cash, cash equivalents, and restricted cash | 921 | 2,037 | $ 1,829 | $ 1,068
Other current assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 141 | 62 |  |
Other deferred charges and assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 31 | 58 |  |
Alabama Power |  |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |  |
Cash and cash equivalents | 324 | 687 |  |
Restricted cash: |  |  |  |
Total cash, cash equivalents, and restricted cash | 409 | 687 | 1,060 | 530
Alabama Power | Other current assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 85 | 0 |  |
Alabama Power | Other deferred charges and assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 0 | 0 |  |
Georgia Power |  |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |  |
Cash and cash equivalents | 9 | 364 |  |
Restricted cash: |  |  |  |
Total cash, cash equivalents, and restricted cash | 75 | 480 | 33 | 9
Georgia Power | Other current assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 37 | 60 |  |
Georgia Power | Other deferred charges and assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 29 | 56 |  |
Southern Power |  |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |  |
Cash and cash equivalents | 124 | 131 |  |
Restricted cash: |  |  |  |
Total cash, cash equivalents, and restricted cash | 144 | 133 | 135 | 182
Southern Power | Other current assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 17 | 0 |  |
Southern Power | Other deferred charges and assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 3 | 3 |  |
Southern Power | Estimated Construction Completion Costs | Deuel Harvest |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 3 | 3 |  |
Southern Power | Proceeds From Issuance Of Solid Waste Disposal Facility Revenue Bonds |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 17 |  |  |
Southern Company Gas |  |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |  |
Cash and cash equivalents | 33 | 81 |  |
Restricted cash: |  |  |  |
Total cash, cash equivalents, and restricted cash | 35 | 83 | $ 48 | $ 19
Southern Company Gas | Other current assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | 2 | 2 |  |
Southern Company Gas | Other deferred charges and assets |  |  |  |
Restricted cash: |  |  |  |
Restricted cash | $ 0 | $ 0 |  |

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