CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Income Statement Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			$ 76	$ 153	$ 162
Impairment charges			2	0	168
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			50	141	157
Impairment charges			0	0	115
Southern Company Gas | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			127	129	141
Southern Company Gas | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			0	3	13
Southern Company Gas | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			(81)	7	6
Impairment charges	$ 2	$ 82	84
Southern Company Gas | Other
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			$ 4	$ 2	$ (3)