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REGULATORY MATTERS - MPC System Restoration Rider (Details) - USD ($) |  |  |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Dec. 07, 2021 | Jun. 08, 2021 | Apr. 06, 2021 | Mar. 31, 2020 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Oct. 14, 2021
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Minimum annual accrual, amount | $ 8,000,000 |  |  |  |  |  |  |
Major storms |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Storm damage reserves accrual |  |  |  |  | $ 286,000,000 | $ 326,000,000 | $ 170,000,000 |
Mississippi Power |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Threshold above which actual damages are charged to the reserve (individually exceed) |  |  |  |  | 50,000 |  |  |
Public utilities, approved rate increase (decrease), amount | 9,000,000 | $ 16,000,000 | $ 28,000,000 | $ (16,700,000) |  |  |  |
Target property damage reserve | $ 75,000,000 |  |  |  |  |  |  |
Mississippi Power | Hurricanes Zeta and Ida Accounting Order |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Regulatory asset |  |  |  |  |  |  |  | $ 49,000,000
Mississippi Power | Retail electric revenues |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Property damage reserve |  |  |  |  | 31,000,000 | 4,000,000 |  |
Mississippi Power | Major storms |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Storm damage reserves accrual |  |  |  |  | $ (1,800,000) | $ 800,000 | $ 1,400,000 |

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