CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Balance Sheet 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]
Equity investments in unconsolidated subsidiaries			$ 1,282	$ 1,362
Impairment charges			2	0	$ 168
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries			1,173	1,290
Impairment charges			0	0	$ 115
SNG | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries			1,129	1,167
PennEast Pipeline | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries			11	91
Impairment charges	$ 2	$ 82	84
Other | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries			$ 33	$ 32