Segment and Related Information - Schedule of Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Concentration Risk [Line Items]
Operating revenues	$ 5,910	$ 5,018
Less Gross Gas Costs	583	439
Retail
Concentration Risk [Line Items]
Operating revenues	3,342	3,078
Wholesale
Concentration Risk [Line Items]
Operating revenues	545	418
Other
Concentration Risk [Line Items]
Operating revenues	170	151
Electric Utilities' Revenues
Concentration Risk [Line Items]
Operating revenues	4,117	3,695
Electric Utilities' Revenues | Retail
Concentration Risk [Line Items]
Operating revenues	3,342	3,078
Electric Utilities' Revenues | Wholesale
Concentration Risk [Line Items]
Operating revenues	545	418
Electric Utilities' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	230	199
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues	1,694	1,249
Southern Company Gas' Revenues | Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues	1,192	1,013
Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	298	51
Southern Company Gas' Revenues | Gas marketing services
Concentration Risk [Line Items]
Operating revenues	195	177
Southern Company Gas' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	9	8
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues	1,694	1,249
Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	298	51
Less Gross Gas Costs	2,353	1,163
Third Party Gross Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	2,588	1,185
Intercompany Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	63	29
Total Gross Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	$ 2,651	$ 1,214