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INCOME TAXES - Narrative (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | $ 8,914 | $ 8,914 | $ 8,914 | $ 8,874 |
ITC and PTC carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 1,750 | 1,750 | 1,750 | 1,853 |
Southern Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 1,258 | 1,258 | $ 1,258 | 1,587 |
Percentage reduction in tax basis of assets |  |  | 50.00% |  |
Southern Power | ITCs and other credits carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Reduction in income tax expense, investment tax credits |  |  | $ 289 | 340 | $ 734
Southern Power | ITC and PTC carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 827 | 827 | 827 | 1,110 |
Southern Power | ITC and PTC carryforward | Nacogdoches Biomass Generating Plant |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Reduction in income tax expense, investment tax credits |  |  |  |  | 5
Southern Power | Production Tax Credit Carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Effective income tax rate reconciliation, tax credit, production, amount |  |  | 16 | 15 | 12
Georgia Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 4,019 | 4,019 | 4,019 | 3,443 |
State investment tax credit carryforward |  |  | 428 |  |
Georgia Power | ITC and PTC carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 704 | 704 | 704 | 539 |
Mississippi Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 393 | 393 | 393 | 428 |
Mississippi Power | ITC and PTC carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 0 | 0 | 0 | 0 |
Southern Company Gas |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 328 | 328 | 328 | 432 |
Southern Company Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Sequent |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred tax expense, increase from change in appointment rate | 85 | 85 | 85 |  |
Southern Company Gas | ITC and PTC carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 0 | 0 | 0 | 0 |
State and Local Jurisdiction | Georgia Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Valuation allowance | 58 | 58 | 58 |  |
State and Local Jurisdiction | Georgia Power | ITCs and other credits carryforward |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Reduction in income tax expense, investment tax credits |  |  | 66 | 67 | 51
State and Local Jurisdiction | Southern Company Gas |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Valuation allowance |  |  |  |  | 5
Deferred Charges Related To Income Taxes, Current | Other Noncurrent Assets | Southern Power | Unrealized Tax Credits |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Deferred income tax assets | 6 | 6 | 6 | $ 5 | $ 51
Mississippi | State and Local Jurisdiction | Mississippi Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Operating loss carryforwards, valuation allowance | 32 | 32 | 32 |  |
New York | State and Local Jurisdiction | Southern Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Operating loss carryforwards, valuation allowance | 25 | 25 | 25 |  |
Oklahoma | State and Local Jurisdiction | Southern Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Operating loss carryforwards, valuation allowance | 11 | 11 | 11 |  |
Florida | State and Local Jurisdiction | Southern Power |  |  |  |  |
Income Tax Disclosure [Line Items] |  |  |  |  |
Operating loss carryforwards, valuation allowance | $ 10 | $ 10 | $ 10 |  |

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