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Fair Value Measurements - Schedule of Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Billions	Sep. 30, 2025 USD ($)
Long-term debt, including securities due within one year:
Carrying amount	$ 71.9
Fair value	68.4
ALABAMA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	12.0
Fair value	10.9
GEORGIA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	20.8
Fair value	19.5
MISSISSIPPI POWER CO
Long-term debt, including securities due within one year:
Carrying amount	1.8
Fair value	1.6
SOUTHERN POWER CO
Long-term debt, including securities due within one year:
Carrying amount	3.8
Fair value	3.8
SOUTHERN Co GAS
Long-term debt, including securities due within one year:
Carrying amount	9.3
Fair value	$ 8.5

X

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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No definition available.

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