Segment and Related Information - Schedule of Financial Data for Products and Services (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
	Jul. 01, 2021	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Concentration Risk [Line Items]
Operating revenues			$ 6,238	$ 5,620	$ 17,346	$ 15,258
Gain on sale					171	36
Retail
Concentration Risk [Line Items]
Operating revenues			4,551	4,243	11,492	10,503
Wholesale
Concentration Risk [Line Items]
Operating revenues			731	584	1,822	1,473
Other
Concentration Risk [Line Items]
Operating revenues			179	164	525	484
Electric Utilities' Revenues
Concentration Risk [Line Items]
Operating revenues			5,527	5,049	14,051	12,628
Electric Utilities' Revenues | Retail
Concentration Risk [Line Items]
Operating revenues			4,551	4,243	11,492	10,503
Electric Utilities' Revenues | Wholesale
Concentration Risk [Line Items]
Operating revenues			731	584	1,822	1,473
Electric Utilities' Revenues | Other
Concentration Risk [Line Items]
Operating revenues			245	222	737	652
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues			623	477	2,994	2,362
Southern Company Gas' Revenues | Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues			553	476	2,451	2,072
Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	(51)	188	(19)
Southern Company Gas' Revenues | Gas marketing services
Concentration Risk [Line Items]
Operating revenues			52	39	311	272
Southern Company Gas' Revenues | Other
Concentration Risk [Line Items]
Operating revenues			18	13	44	37
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues			623	477	2,994	2,362
Gain on sale					127	(2)
Deferred tax expense, increase from change in appointment rate			85		85
Asset impairment charges					84	0
Southern Company Gas' Revenues | Disposal Group, Disposed of by Sale | Sequent
Concentration Risk [Line Items]
Gain on sale	$ 121
Gain on sale, net of tax	$ 93
Deferred tax expense, increase from change in appointment rate		$ 85
Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	(51)	188	(19)
Less Gross Gas Costs			0	1,134	3,783	3,189
Third Party Gross Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	1,050	3,881	3,089
Intercompany Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	33	90	81
Total Gross Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			$ 0	$ 1,083	$ 3,971	$ 3,170