SEGMENT AND RELATED INFORMATION - Gas Revenues (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 01, 2021	Dec. 31, 2020	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total operating revenues							$ 23,113	$ 20,375	$ 21,419
Impairment charges							2	0	168
Gain on dispositions, net							176	66	2,588
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues							4,380	3,434	3,792
Impairment charges							0	0	115
Gain on dispositions, net							127	22	0
Southern Company Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Sequent
Segment Reporting Information [Line Items]
Gain on dispositions, net	$ 121						121
Gain (loss) on dispositions, after tax	$ 92						92
Deferred tax expense, increase from change in appointment rate					$ 85	$ 85	85
Southern Company Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Jefferson Island | Natural Gas Storage Facility
Segment Reporting Information [Line Items]
Impairment charges								91
Impairment charges, after tax								69
Gain on dispositions, net		$ 22
Gain (loss) on dispositions, after tax		$ 16
Southern Company Gas | PennEast Pipeline
Segment Reporting Information [Line Items]
Impairment charges			$ 2	$ 82			84
Impairment charges, after tax			$ 2	$ 58			67
Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues							4,374	3,466	3,810
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues							4,380	3,434	3,792
Southern Company Gas | Gas distribution operations
Segment Reporting Information [Line Items]
Total operating revenues							3,656	2,902	3,001
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues							475	408	456
Southern Company Gas | Other Gas Revenue
Segment Reporting Information [Line Items]
Total operating revenues							249	124	335
Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues							4,380	3,434	3,792
Wholesale gas services | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues							188	74	294
Less Gross Gas Costs							3,783	4,585	5,684
Wholesale gas services | Operating Segments | Third Party Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues							3,881	4,544	5,703
Wholesale gas services | Operating Segments | Intercompany Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues							90	115	275
Wholesale gas services | Operating Segments | Total Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues							$ 3,971	$ 4,659	$ 5,978