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Fair Value Measurements - Schedule of Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Billions	Jun. 30, 2025 USD ($)
Long-term debt, including securities due within one year:
Carrying amount	$ 68.1
Fair value	63.6
ALABAMA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	11.5
Fair value	10.3
GEORGIA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	19.3
Fair value	17.7
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	2.7
Fair value	2.7
SOUTHERN Co GAS
Long-term debt, including securities due within one year:
Carrying amount	8.5
Fair value	$ 7.5

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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