Introduction - Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 6,223	$ 2
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	906
Other intangibles subject to amortization - accumulated amortization	(39)	(12)
Other intangibles subject to amortization - net	867
Total other intangible assets - gross	981
Total other intangible assets - net	942	317
Southern Company [Member]
Goodwill [Line Items]
Goodwill	6,223
Southern Power [Member]
Goodwill [Line Items]
Goodwill	2	2
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - accumulated amortization	(16)	(12)
Total other intangible assets - net	$ 389	$ 317
Customer relationships [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	11 years
Customer relationships [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	26 years
Customer relationships [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 268
Other intangibles subject to amortization - accumulated amortization	(16)
Other intangibles subject to amortization - net	$ 252
Trade names [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	5 years
Trade names [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	28 years
Trade names [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 158
Other intangibles subject to amortization - accumulated amortization	(3)
Other intangibles subject to amortization - net	$ 155
Patents [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	3 years
Patents [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Patents [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 4
Other intangibles subject to amortization - accumulated amortization	0
Other intangibles subject to amortization - net	$ 4
Backlog [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	5 years
Other intangibles subject to amortization - gross carrying amount	$ 5
Other intangibles subject to amortization - accumulated amortization	0
Other intangibles subject to amortization - net	$ 5
Storage and transportation contracts [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	1 year
Storage and transportation contracts [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	5 years
Storage and transportation contracts [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 64
Other intangibles subject to amortization - accumulated amortization	(4)
Other intangibles subject to amortization - net	$ 60
Software and other [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	1 year
Software and other [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	12 years
Software and other [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 2
Other intangibles subject to amortization - accumulated amortization	0
Other intangibles subject to amortization - net	$ 2
PPA fair value adjustments [Member] | Southern Company [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	19 years
PPA fair value adjustments [Member] | Southern Company [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	20 years
PPA fair value adjustments [Member] | Southern Power [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 405
Other intangibles subject to amortization - accumulated amortization	(16)
Other intangibles subject to amortization - net	$ 389
PPA fair value adjustments [Member] | Southern Power [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	19 years
PPA fair value adjustments [Member] | Southern Power [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	20 years
FCC Licenses [Member] | Southern Company [Member]
Indefinite-lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	$ 75