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Derivatives - Schedule of Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions | 9 Months Ended
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Sep. 30, 2025 USD ($)
Derivative [Line Items] |
Notional Amount | $ 2,465
Fair Value Gain (Loss) | (184)
Southern Company parent | Fair Value Hedges of Existing Debt | Date One |
Derivative [Line Items] |
Notional Amount | $ 400
Weighted Average Interest Rate Paid | 0.80%
Interest Rate Received | 1.75%
Fair Value Gain (Loss) | $ (23)
Southern Company parent | Fair Value Hedges of Existing Debt | Date Two |
Derivative [Line Items] |
Notional Amount | $ 1,000
Weighted Average Interest Rate Paid | 2.48%
Interest Rate Received | 3.70%
Fair Value Gain (Loss) | $ (108)
Southern Company parent | Fair Value Hedges of Existing Debt | Date Three |
Derivative [Line Items] |
Notional Amount | $ 565
Weighted Average Interest Rate Paid | 1.56%
Interest Rate Received | 6.50%
Fair Value Gain (Loss) | $ 3
SOUTHERN Co GAS | Fair Value Hedges of Existing Debt |
Derivative [Line Items] |
Fair Value Gain (Loss) | (56)
SOUTHERN Co GAS | Fair Value Hedges of Existing Debt | Date One |
Derivative [Line Items] |
Notional Amount | $ 500
Weighted Average Interest Rate Paid | 0.49%
Interest Rate Received | 1.75%

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