Introduction - Other Intangibles (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 980,000,000	$ 957,000,000
Accumulated Amortization	(126,000,000)	(62,000,000)
Other Intangible Assets, Net	854,000,000	895,000,000
Total other intangible assets - gross	1,055,000,000	1,032,000,000
Total other intangible assets - net	929,000,000	970,000,000
Customer relationships | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	288,000,000	268,000,000
Accumulated Amortization	(57,000,000)	(32,000,000)
Other Intangible Assets, Net	231,000,000	236,000,000
Trade names | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	159,000,000	158,000,000
Accumulated Amortization	(11,000,000)	(5,000,000)
Other Intangible Assets, Net	148,000,000	153,000,000
Patents | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	4,000,000	4,000,000
Accumulated Amortization	0	0
Other Intangible Assets, Net	4,000,000	4,000,000
Backlog | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	5,000,000	5,000,000
Accumulated Amortization	(1,000,000)	(1,000,000)
Other Intangible Assets, Net	4,000,000	4,000,000
Storage and transportation contracts | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64,000,000	64,000,000
Accumulated Amortization	(21,000,000)	(2,000,000)
Other Intangible Assets, Net	43,000,000	62,000,000
Software and other | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	4,000,000	2,000,000
Accumulated Amortization	(1,000,000)	0
Other Intangible Assets, Net	3,000,000	2,000,000
PPA fair value adjustments | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456,000,000	456,000,000
Accumulated Amortization	(35,000,000)	(22,000,000)
Other Intangible Assets, Net	421,000,000	434,000,000
Federal Communications Commission licenses | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	75,000,000	75,000,000
SOUTHERN POWER CO
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(35,000,000)	(22,000,000)
SOUTHERN POWER CO | PPA fair value adjustments
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456,000,000	456,000,000
Accumulated Amortization	(35,000,000)	(22,000,000)
Other Intangible Assets, Net	421,000,000	434,000,000
SOUTHERN Co GAS
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	400,000,000	400,000,000
Accumulated Amortization	(80,000,000)	(34,000,000)
Other Intangible Assets, Net	320,000,000	366,000,000
Total other intangible assets - net	320,000,000	366,000,000
SOUTHERN Co GAS | Customer relationships
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	221,000,000	221,000,000
Accumulated Amortization	(53,000,000)	(30,000,000)
Other Intangible Assets, Net	168,000,000	191,000,000
SOUTHERN Co GAS | Trade names
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	115,000,000	115,000,000
Accumulated Amortization	(6,000,000)	(2,000,000)
Other Intangible Assets, Net	109,000,000	113,000,000
SOUTHERN Co GAS | Storage and transportation contracts
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64,000,000	64,000,000
Accumulated Amortization	(21,000,000)	(2,000,000)
Other Intangible Assets, Net	$ 43,000,000	$ 62,000,000