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REGULATORY MATTERS - APC Rate CNP (Details) - Alabama Power - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2022 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |
Under recovered certified power purchase agreements | $ 120 | $ 103 | $ 120 |
Retail revenue requirement for environmental compliance |  | $ 23 | $ 255 | $ 59
Retail revenue requirement for environmental compliance, as a percentage |  | (0.30%) | 3.70% |
Over (under) recovered environmental clause | (47) | $ (33) | $ (47) |
Public utilities, approved rate increase (decrease), amount | $ 318 |  |  |
Approved rate increase, percent | 4.60% |  |  |
Other regulatory assets, current |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |
Under recovered certified power purchase agreements | $ 18 | 18 | 18 |
Over (under) recovered environmental clause |  | (8) |  |
Other regulatory assets, deferred |  |  |  |
Schedule of Regulatory Assets and Liabilities [Line Items] |  |  |  |
Under recovered certified power purchase agreements | $ 102 | 85 | $ 102 |
Over (under) recovered environmental clause |  | $ (25) |  |

X
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