Introduction - Other Intangibles (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 983	$ 957
Accumulated Amortization	(156)	(62)
Other Intangible Assets, Net	827	895
Total other intangible assets - gross	1,058	1,032
Total other intangible assets - net	902	970
Customer relationships | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	288	268
Accumulated Amortization	(70)	(32)
Other Intangible Assets, Net	218	236
Trade names | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	159	158
Accumulated Amortization	(15)	(5)
Other Intangible Assets, Net	144	153
Storage and transportation contracts | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(27)	(2)
Other Intangible Assets, Net	37	62
PPA fair value adjustments | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(41)	(22)
Other Intangible Assets, Net	415	434
Other | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	16	11
Accumulated Amortization	(3)	(1)
Other Intangible Assets, Net	13	10
Federal Communications Commission licenses | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	75	75
SOUTHERN POWER CO
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(41)	(22)
SOUTHERN POWER CO | PPA fair value adjustments
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(41)	(22)
Other Intangible Assets, Net	415	434
SOUTHERN Co GAS
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	400	400
Accumulated Amortization	(100)	(34)
Other Intangible Assets, Net	300	366
Total other intangible assets - net	300	366
SOUTHERN Co GAS | Customer relationships
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	221	221
Accumulated Amortization	(65)	(30)
Other Intangible Assets, Net	156	191
SOUTHERN Co GAS | Trade names
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	115	115
Accumulated Amortization	(8)	(2)
Other Intangible Assets, Net	107	113
SOUTHERN Co GAS | Storage and transportation contracts
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(27)	(2)
Other Intangible Assets, Net	$ 37	$ 62