Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 306	$ 266
ALABAMA POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Rate CNP Compliance	12	16
Rate CNP PPA	84	84
Retail Energy Cost Recovery	46	126
GEORGIA POWER CO | Other deferred charges and assets
Loss Contingencies [Line Items]
Fuel Cost Recovery	494	410
MISSISSIPPI POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Ad Valorem Tax	33	37
MISSISSIPPI POWER CO | Other customer accounts receivable
Loss Contingencies [Line Items]
Fuel Cost Recovery	16	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	306	266
SOUTHERN Co GAS | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Natural gas cost under recovery	44	207
SOUTHERN Co GAS | Other regulatory assets, current
Loss Contingencies [Line Items]
Natural gas cost under recovery	306	266
SOUTHERN Co GAS | Other regulatory liabilities, current
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 13	$ 0