Segment and Related Information - Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Concentration Risk [Line Items]
Operating revenues	$ 5,098	$ 5,627	$ 10,510	$ 11,999
Retail
Concentration Risk [Line Items]
Operating revenues	3,540	3,740	6,623	7,308
Wholesale
Concentration Risk [Line Items]
Operating revenues	542	616	1,041	1,239
Other
Concentration Risk [Line Items]
Operating revenues	161	170	331	330
Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues	562	642	1,724	1,865
Electric Utilities' Revenues
Concentration Risk [Line Items]
Operating revenues	4,290	4,565	8,085	8,948
Electric Utilities' Revenues | Retail
Concentration Risk [Line Items]
Operating revenues	3,540	3,740	6,623	7,308
Electric Utilities' Revenues | Wholesale
Concentration Risk [Line Items]
Operating revenues	542	616	1,041	1,239
Electric Utilities' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	208	209	421	401
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues	689	730	2,163	2,369
Southern Company Gas' Revenues | Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues	563	638	1,724	1,838
Southern Company Gas' Revenues | Gas Distribution Operations | Revenues | Product Concentration Risk | Three Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues		70		237
Southern Company Gas' Revenues | Gas Marketing Services
Concentration Risk [Line Items]
Operating revenues	58	89	287	359
Southern Company Gas' Revenues | Gas Marketing Services | Revenues | Product Concentration Risk | Pivotal Home Solutions
Concentration Risk [Line Items]
Operating revenues		24		55
Southern Company Gas' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	$ 68	$ 3	$ 152	$ 172