Introduction - Other Intangibles (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	$ (205)	$ (186)
Total other intangible assets - net	702	873
Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	832	984
Accumulated Amortization	(205)	(186)
Other Intangible Assets, Net	627	798
Total other intangible assets - gross	907	1,059
Total other intangible assets - net	702	873
Customer relationships | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	223	288
Accumulated Amortization	(79)	(83)
Other Intangible Assets, Net	144	205
Trade names | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	70	159
Accumulated Amortization	(17)	(17)
Other Intangible Assets, Net	53	142
Storage and transportation contracts | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(44)	(34)
Other Intangible Assets, Net	20	30
PPA fair value adjustments | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(60)	(47)
Other Intangible Assets, Net	396	409
Other | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	19	17
Accumulated Amortization	(5)	(5)
Other Intangible Assets, Net	14	12
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	(60)	(47)
SOUTHERN POWER CO | PPA fair value adjustments
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(60)	(47)
Other Intangible Assets, Net	396	409
SOUTHERN Co GAS
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	246	400
Accumulated Amortization	(121)	(120)
Other Intangible Assets, Net	125	280
Total other intangible assets - net	125	280
SOUTHERN Co GAS | Customer relationships
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	156	221
Accumulated Amortization	(71)	(77)
Other Intangible Assets, Net	85	144
SOUTHERN Co GAS | Trade names
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	26	115
Accumulated Amortization	(6)	(9)
Other Intangible Assets, Net	20	106
SOUTHERN Co GAS | Storage and transportation contracts
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(44)	(34)
Other Intangible Assets, Net	$ 20	$ 30