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REGULATORY MATTERS - MPC Fuel Cost Recovery and Ad Valorem Tax Adjustment (Details) - Mississippi Power - USD ($) $ in Millions |  |  |  | 1 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Dec. 07, 2021 | Jun. 08, 2021 | Apr. 06, 2021 | Feb. 28, 2022 | Jan. 31, 2022 | Feb. 28, 2021 | Jan. 31, 2021 | Mar. 31, 2020 | Feb. 29, 2020 | Jan. 31, 2020 | Feb. 28, 2019 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount | $ 9.0 | $ 16.0 | $ 28.0 |  |  |  |  | $ (16.7) |  |  |  |  |  |
PSC retail increase |  |  |  |  |  |  |  |  |  |  |  |  | $ 10.0 | $ 2.0
Public utilities, valorem taxes previously recovered, amount |  |  | $ 19.0 |  |  |  |  |  |  |  |  |  |  |
Retail electric revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  |  |  |  | $ 2.0 |  |  | $ (24.0) |  | $ (35.0) |  |  |
Over recovered fuel cost |  |  |  |  |  |  |  |  |  |  |  | $ 4.0 | 24.0 |
Retail electric revenues | Scenario, Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  |  | $ 43.0 |  |  |  |  |  |  |  |  |  |
MRA Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  |  |  |  |  | $ 5.0 |  |  | $ 1.0 |  |  |  |
Over recovered fuel cost |  |  |  |  |  |  |  |  |  |  |  |  | $ 10.0 |
MRA Revenue | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount |  |  |  |  | $ 11.0 |  |  |  |  |  |  |  |  |

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