Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 0	$ 108
ALABAMA POWER CO | Other regulatory assets, current
Loss Contingencies [Line Items]
Rate CNP Compliance	23	47
Rate CNP PPA	17	18
Retail Energy Cost Recovery	101	102
ALABAMA POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Rate CNP Compliance	18	0
Rate CNP PPA	100	102
Retail Energy Cost Recovery	420	520
GEORGIA POWER CO | Receivables – under recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery(*)	447	0
GEORGIA POWER CO | Deferred under recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery(*)	1,702	2,056
MISSISSIPPI POWER CO | Other regulatory assets, current
Loss Contingencies [Line Items]
Ad Valorem Tax	9	12
MISSISSIPPI POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Ad Valorem Tax	19	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	$ 117	$ 0