Fair Value Measurements - Schedule of Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Billions	Jun. 30, 2023 USD ($)
Long-term debt, including securities due within one year:
Carrying amount	$ 58.9
Fair value	53.5
ALABAMA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	10.8
Fair value	9.5
GEORGIA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	16.5
Fair value	15.0
MISSISSIPPI POWER CO
Long-term debt, including securities due within one year:
Carrying amount	1.6
Fair value	1.4
SOUTHERN POWER CO
Long-term debt, including securities due within one year:
Carrying amount	3.0
Fair value	2.8
SOUTHERN Co GAS
Long-term debt, including securities due within one year:
Carrying amount	7.5
Fair value	$ 6.6