Consolidated Entities and Equity Method Investments - Schedule of Earnings from Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	$ (40)	$ 30	$ 5	$ 72
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	(52)	30	(11)	72
Asset impairment charges			82	0
Asset impairment charges, net of tax			58
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	28	28	66	65
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	(81)	1	(79)	3
SOUTHERN Co GAS | Other
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	$ 1	$ 1	$ 2	$ 4