Introduction - Other Intangible Assets Not Subject to Amortization (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	$ (225)	$ (186)
Total other intangible assets - net	674	873
Southern Company
Indefinite-lived Intangible Assets [Line Items]
Total other intangible assets - gross	899	1,059
Accumulated Amortization	(225)	(186)
Total other intangible assets - net	674	873
Federal Communications Commission licenses | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	75	75
SOUTHERN POWER CO
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(66)	(47)
SOUTHERN Co GAS
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(133)	(120)
Total other intangible assets - net	$ 113	$ 280