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	Jul. 31, 2021	Dec. 31, 2020	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total operating revenues								$ 29,279	$ 23,113	$ 20,375
Impairment charges								251	2	0
Gain on dispositions, net								42	176	66
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues								5,962	4,380	3,434
Impairment charges								131	0	0
Gain on dispositions, net								4	127	22
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	85
Southern Company Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Jefferson Island | Natural Gas Storage Facility
Segment Reporting Information [Line Items]
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	84
Impairment charges, after tax				$ 2	$ 58			67	67
Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues								5,937	4,374	3,466
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues								5,962	4,380	3,434
Southern Company Gas | Gas distribution operations
Segment Reporting Information [Line Items]
Total operating revenues								5,240	3,656	2,902
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues								638	475	408
Southern Company Gas | Other Gas Revenue
Segment Reporting Information [Line Items]
Total operating revenues								84	249	124
Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues								5,962	4,380	3,434
Wholesale gas services | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues								$ 0	188	74
Less Gross Gas Costs									3,783	4,585
Wholesale gas services | Operating Segments | Third Party Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									3,881	4,544
Wholesale gas services | Operating Segments | Intercompany Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									90	115
Wholesale gas services | Operating Segments | Total Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									$ 3,971	$ 4,659