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REGULATORY MATTERS - MPC System Restoration Rider and Reliability Reserve Accounting Order (Details) - USD ($) $ in Thousands | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jul. 31, 2024 | Jun. 30, 2023 | Jun. 30, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Apr. 11, 2024 | Apr. 30, 2023 | Mar. 31, 2023
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Reliability reserve, amount deferred |  |  |  | $ 84,000 | $ 63,000 | $ 191,000 |  |  |  |
Net regulatory assets |  |  |  | 7,041,000 | 6,523,000 |  |  |  |  |
Reliability reserves |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  | (188,000) | (179,000) |  |  |  |  |
Major storms |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Storm damage reserves accrual |  |  |  |  |  | 239,000 |  |  |  |
Mississippi Power |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Threshold above which actual damages are charged to the reserve (individually exceed) |  |  |  | 50 |  |  |  |  |  |
Public utilities, approved rate increase (decrease), amount | $ (5,000) | $ (7,000) | $ 18,000 |  |  |  | $ 9,000 |  |  |
Reliability reserve, amount deferred |  |  |  | 21,000 | 11,000 | 25,000 |  | $ 12,600 | $ 11,700 | $ 8,300
Net regulatory assets |  |  |  | 59,000 | 90,000 |  |  |  |  |
Mississippi Power | Reliability reserves |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Net regulatory assets |  |  |  | (57,000) | (36,000) |  |  |  |  |
Mississippi Power | Retail electric revenues |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Property damage reserve |  |  |  | 52,000 | 45,000 |  |  |  |  |
Mississippi Power | Major storms |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Storm damage reserves accrual |  |  |  | $ 12,600 | $ 11,700 | $ 6,900 |  |  |  |

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