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REGULATORY MATTERS - MPC 2019 Base Rate Case and Performance Evaluation Plan (Details) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2023 USD ($) | Jun. 30, 2022 USD ($) | Jun. 30, 2021 USD ($) | May 31, 2021 USD ($) | Dec. 31, 2023 filing | Dec. 31, 2021 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Regulatory asset amortization period |  |  |  |  | 4 years |
Mississippi Power |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount | $ | $ (7) | $ 18 | $ 16 | $ 28 |  | $ 9
Approved rate decrease, percent |  | (1.90%) | (1.80%) |  |  |
Performance evaluation plan, number of filings per calendar year | filing |  |  |  |  | 2 |
Mississippi Power | Weighted Average | Measurement Input, Average Customer Price |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Performance evaluation plan, measurement input |  |  |  |  | 0.40 |
Mississippi Power | Weighted Average | Measurement Input, Service Reliability |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Performance evaluation plan, measurement input |  |  |  |  | 0.40 |
Mississippi Power | Weighted Average | Measurement Input, Customer Satisfaction |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Performance evaluation plan, measurement input |  |  |  |  | 0.20 |

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