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REGULATORY MATTERS - MPC Integrated Resource Plan (Details) $ in Millions | Dec. 31, 2021 USD ($) | Sep. 09, 2021 MW | Dec. 31, 2020 USD ($) MW
--- | --- | --- | ---
Public Utilities, General Disclosures [Line Items] |  |  |
Net regulatory assets | $ | $ 4,711 |  | $ 5,493
Mississippi Power |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Required fossil-stream generation retirements (in MWs) | MW |  |  | 950
Net regulatory assets | $ | 46 |  | $ 136
Mississippi Power | Plant Watson Unit 4 |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Required fossil-stream generation retirements (in MWs) | MW |  | 268 |
Mississippi Power | Plant Greene County Units 1 and 2 |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Required fossil-stream generation retirements (in MWs) | MW |  | 103 |
Percent ownership |  | 40.00% |
Mississippi Power | Plant Greene County Units 1 and 2 | Alabama Power |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Percent ownership |  | 40.00% |
Mississippi Power | Plant Daniel |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Required fossil-stream generation retirements (in MWs) | MW |  | 502 |
Percent ownership |  | 50.00% |
Net regulatory assets | $ | 515 |  |
Estimated amount remaining at retirement | $ | $ 386 |  |

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