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REGULATORY MATTERS - MPC 2019 Base Rate Case and Performance Evaluation Plan (Details) - Mississippi Power $ in Millions |  |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 07, 2021 USD ($) | Jun. 08, 2021 USD ($) | Apr. 06, 2021 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2021 filing
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Public utilities, approved rate increase (decrease), amount | $ 9.0 | $ 16.0 | $ 28.0 | $ (16.7) |
Approved rate decrease, percent |  | (1.80%) |  | 1.85% |
Base rate case filing, measurement input, average equity ratio |  |  |  | 53.00% |
Base rate case filing, measurement input, maximum equity ratio |  |  |  | 55.00% |
Base rate case filing, measurement input, return on investment |  |  |  | 7.57% |
Regulatory asset amortization period |  |  |  | 4 years |
Regulatory liability amortization period |  |  |  | 3 years |
Annual base rate adjustment, increase in depreciation |  |  |  | $ 10.0 |
Annual base rate adjustment, compensation costs excluded |  |  |  | $ 3.9 |
Performance evaluation plan, number of filings per calendar year | filing |  |  |  |  | 2
Weighted Average | Measurement Input, Average Customer Price |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Performance evaluation plan, measurement input |  |  |  |  | 0.40
Weighted Average | Measurement Input, Service Reliability |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Performance evaluation plan, measurement input |  |  |  |  | 0.40
Weighted Average | Measurement Input, Customer Satisfaction |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Performance evaluation plan, measurement input |  |  |  |  | 0.20

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