Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
ALABAMA POWER CO | Other regulatory assets, current
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 0	$ 47
Rate CNP PPA	17	18
Retail Energy Cost Recovery	208	102
ALABAMA POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Rate CNP PPA	90	102
Retail Energy Cost Recovery	80	520
ALABAMA POWER CO | Other Regulatory Liabilities, Deferred
Loss Contingencies [Line Items]
Rate CNP Compliance	3	0
GEORGIA POWER CO | Receivables – under recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery(*)	730	0
GEORGIA POWER CO | Deferred under recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery(*)	1,279	2,056
MISSISSIPPI POWER CO | Other regulatory assets, current
Loss Contingencies [Line Items]
Ad Valorem Tax	3	12
MISSISSIPPI POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Ad Valorem Tax	11	19
MISSISSIPPI POWER CO | Receivables – customer accounts, net
Loss Contingencies [Line Items]
Fuel Cost Recovery(*)	25	1
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Natural gas cost under recovery	0	108
SOUTHERN Co GAS | Other regulatory assets, current
Loss Contingencies [Line Items]
Natural gas cost under recovery	0	108
SOUTHERN Co GAS | Natural gas cost over recovery
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 165	$ 0