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Derivatives - Schedule of Foreign Currency Derivatives (Details) - 9 months ended Sep. 30, 2025 - Foreign currency derivatives € in Millions, $ in Millions | USD ($) | EUR (€)
--- | --- | ---
Derivative [Line Items] |  |
Pay Notional | $ 2,040 |
Receive Notional | € |  | € 1,750
Fair Value Gain (Loss) | 10 |
Cash Flow Hedges of Forecasted Debt | SOUTHERN POWER CO |  |
Derivative [Line Items] |  |
Pay Notional | $ 564 |
Pay Rate | 3.78% |
Receive Notional | € |  | 500
Receive Rate | 1.85% |
Fair Value Gain (Loss) | $ 20 |
Fair Value Hedges of Existing Debt | Southern Company parent |  |
Derivative [Line Items] |  |
Pay Notional | $ 1,476 |
Pay Rate | 3.39% |
Receive Notional | € |  | € 1,250
Receive Rate | 1.88% |
Fair Value Gain (Loss) | $ (10) |

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