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Regulatory Matters - MPC (Details) $ in Millions |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 05, 2025 USD ($) | Jul. 30, 2025 USD ($) | Jul. 08, 2025 MW | Jun. 17, 2025 USD ($) | Apr. 03, 2025 USD ($) | Apr. 01, 2025 USD ($) | Mar. 17, 2025 USD ($) | Apr. 11, 2024 USD ($) | Jul. 31, 2025 USD ($) | Apr. 30, 2025 USD ($) | Sep. 30, 2025 USD ($) | Jun. 19, 2025 USD ($) | Jun. 16, 2025 USD ($)
MISSISSIPPI POWER CO |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  |  |  |  | $ 8.0 |  |  |  |  |  |  |
MISSISSIPPI POWER CO | Plant Daniel Units 1 and 2 |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Proportionate ownership share |  |  |  |  |  |  |  |  |  |  |  | 50.00% |
Proceeds from acquisition |  | $ 36.0 |  |  |  |  |  |  |  |  |  |  |
MISSISSIPPI POWER CO | Affiliate PPA |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Requested additional generating capacity (in MWs) | MW |  |  | 50 |  |  |  |  |  |  |  |  |  |
Approved capacity increase (in MWs) | MW |  |  | 750 |  |  |  |  |  |  |  |  |  |
MISSISSIPPI POWER CO | Reliability Reserve Liability |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in accrual |  |  |  |  |  |  | $ 10.9 |  |  |  |  |  |
Remaining net book value |  |  |  |  |  |  | $ 57.0 |  |  |  |  |  |
MISSISSIPPI POWER CO | Mississippi PSC PEP Filing |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Requested revenues increase (decrease) percentage |  |  |  | 4.00% |  |  |  |  |  |  |  |  |
Requested rate increase amount |  |  |  | $ 41.0 |  |  |  |  |  |  |  |  |
Approved rate increase, percentage |  |  |  | 2.00% |  |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  |  |  |  |  |  |  | $ 19.0 | $ 22.0 |  |  |
MISSISSIPPI POWER CO | Mississippi PSC |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  |  |  |  | $ 6.0 |  |  |  |  |  |  |
MISSISSIPPI POWER CO | Ad Valorem Tax Adjustment |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase amount | $ 7.0 |  |  |  |  |  |  |  |  |  |  |  |
MISSISSIPPI POWER CO | Mississippi PSC SRR Filing |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  |  | $ 13.5 |  |  |  |  |  |  |  |  |
Minimum annual accrual, amount |  |  |  |  |  |  |  | $ 12.6 |  |  |  |  |
Property damage reserve |  |  |  | $ 125.0 |  |  |  |  |  |  |  |  | $ 75.0
MISSISSIPPI POWER CO | FERC |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase, percentage |  |  |  |  | 2.50% |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  |  |  | $ 1.0 |  |  |  |  |  |  |  |
Customer refund payments |  |  |  |  | $ 4.0 |  |  |  |  |  |  |  |
ALABAMA POWER CO | Reliability Reserve Liability |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in accrual |  |  |  |  |  |  |  |  |  |  | $ 30.0 |  |
Remaining net book value |  |  |  |  |  |  |  |  |  |  | 101.0 | $ 131.0 |
ALABAMA POWER CO | Regulatory Liability, Nuclear PTC |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining net book value |  |  |  |  |  |  |  |  |  |  | $ 36.0 |  |

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