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REGULATORY MATTERS - MPC Fuel Cost Recovery and Ad Valorem Tax Adjustment (Details) - Mississippi Power - USD ($) $ in Millions |  | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Feb. 06, 2024 | Jan. 31, 2024 | Jun. 30, 2023 | Jan. 31, 2023 | Nov. 30, 2022 | Jul. 31, 2022 | Jun. 30, 2022 | Feb. 28, 2022 | Jan. 31, 2022 | Jun. 30, 2021 | May 31, 2021 | Feb. 28, 2021 | Dec. 31, 2021 | Dec. 31, 2023 | Dec. 31, 2022
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  | $ (7) |  |  |  | $ 18 |  |  | $ 16 | $ 28 |  | $ 9 |  |
Public utilities, valorem taxes previously recovered, amount |  |  |  |  |  |  |  |  |  |  | $ 19 |  |  |  |
Ad Valorem Tax Adjustment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  |  |  |  | $ 5 |  |  |  |  |  |  |  |  |
Retail electric revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  | $ 25 |  | $ 25 |  |  | $ 43 |  |  |  | $ 2 |  |  |
Over (under) recovered fuel cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (50) | $ (1)
Retail electric revenues | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount | $ 18 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovered fuel cost | $ (61) |  |  |  |  |  |  |  |  |  |  |  |  |  |
MRA Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  |  | $ 22 |  |  |  |  | $ 11 |  |  |  |  |  |
Over (under) recovered fuel cost |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 | $ (6)
MRA Revenue | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  | $ (4) |  |  |  |  |  |  |  |  |  |  |  |  |
Retail ECM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovered fuel cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 27 |

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