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CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Environmental Remediation (Details) | 12 Months Ended
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Dec. 31, 2021 USD ($) state site | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Georgia Power |  |  |
Environmental Exit Cost [Line Items] |  |  |
Costs recovered annually | $ 12,000,000 | $ 12,000,000 | $ 2,000,000
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract] |  |  |
Environmental remediation liability, current | 17,000,000 | 15,000,000 |
Accrued environmental remediation | 0 | 0 |
Under recovered environmental remediation costs, other regulatory assets, current | 12,000,000 | 12,000,000 |
Under recovered environmental remediation costs, other regulatory assets, deferred | 23,000,000 | 29,000,000 |
Southern Company Gas |  |  |
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract] |  |  |
Environmental remediation liability, current | 52,000,000 | 29,000,000 |
Accrued environmental remediation | 197,000,000 | 216,000,000 |
Under recovered environmental remediation costs, other regulatory assets, current | 59,000,000 | 34,000,000 |
Under recovered environmental remediation costs, other regulatory assets, deferred | $ 208,000,000 | 236,000,000 |
Southern Company Gas | Manufactured Gas Plants |  |  |
Environmental Exit Cost [Line Items] |  |  |
Number of sites | site | 40 |  |
Number of states in which subject to environmental remediation liabilities | state | 4 |  |
Alabama Power |  |  |
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract] |  |  |
Environmental remediation liability, current | $ 0 | 0 |
Southern Company |  |  |
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract] |  |  |
Environmental remediation liability, current | 69,000,000 | 44,000,000 |
Accrued environmental remediation | 197,000,000 | 216,000,000 |
Under recovered environmental remediation costs, other regulatory assets, current | 71,000,000 | 46,000,000 |
Under recovered environmental remediation costs, other regulatory assets, deferred | $ 231,000,000 | $ 265,000,000 |

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