Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 390	$ 266
ALABAMA POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Rate CNP Compliance	0	16
Rate CNP PPA	125	84
Retail Energy Cost Recovery	413	126
ALABAMA POWER CO | Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Rate CNP Compliance	4	0
ALABAMA POWER CO | Other regulatory assets, current
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	93	0
GEORGIA POWER CO | Other deferred charges and assets
Loss Contingencies [Line Items]
Fuel Cost Recovery	1,697	410
MISSISSIPPI POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Ad Valorem Tax	22	37
MISSISSIPPI POWER CO | Other customer accounts receivable
Loss Contingencies [Line Items]
Fuel Cost Recovery	13	4
MISSISSIPPI POWER CO | Other regulatory assets, current
Loss Contingencies [Line Items]
Ad Valorem Tax	12	12
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Natural gas cost under recovery	390	266
SOUTHERN Co GAS | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Natural gas cost under recovery	0	207
SOUTHERN Co GAS | Other regulatory assets, current
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 390	$ 266