Consolidated Entities and Equity Method Investments - Schedule of Equity Method Investments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 1,368	$ 1,362
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,290	1,290
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,164	1,167
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Investment Balance	93	91
SOUTHERN Co GAS | Other
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 33	$ 32