Introduction - Goodwill and Intangible Assets (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 6,251,000,000	$ 6,251,000,000
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	957,000,000	957,000,000
Other intangibles subject to amortization - accumulated amortization	(97,000,000)	(62,000,000)
Other intangibles subject to amortization - net	860,000,000	895,000,000
Total other intangible assets - gross	1,032,000,000	1,032,000,000
Total other intangible assets - net	$ 935,000,000	970,000,000
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
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
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
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
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
Southern Company [Member] | FCC Licenses [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	$ 75,000,000	75,000,000
Southern Company [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	268,000,000	268,000,000
Other intangibles subject to amortization - accumulated amortization	(44,000,000)	(32,000,000)
Other intangibles subject to amortization - net	224,000,000	236,000,000
Southern Company [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	158,000,000	158,000,000
Other intangibles subject to amortization - accumulated amortization	(8,000,000)	(5,000,000)
Other intangibles subject to amortization - net	150,000,000	153,000,000
Southern Company [Member] | Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	4,000,000	4,000,000
Other intangibles subject to amortization - accumulated amortization	0	0
Other intangibles subject to amortization - net	4,000,000	4,000,000
Southern Company [Member] | Backlog [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	5,000,000	5,000,000
Other intangibles subject to amortization - accumulated amortization	(1,000,000)	(1,000,000)
Other intangibles subject to amortization - net	4,000,000	4,000,000
Southern Company [Member] | Storage and transportation contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	64,000,000	64,000,000
Other intangibles subject to amortization - accumulated amortization	(15,000,000)	(2,000,000)
Other intangibles subject to amortization - net	49,000,000	62,000,000
Southern Company [Member] | Software and other [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	2,000,000	2,000,000
Other intangibles subject to amortization - accumulated amortization	(1,000,000)	0
Other intangibles subject to amortization - net	1,000,000	2,000,000
Southern Company [Member] | PPA fair value adjustments [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangibles subject to amortization - accumulated amortization	(28,000,000)	(22,000,000)
Other intangibles subject to amortization - net	$ 428,000,000	434,000,000
Southern Company [Member] | PPA fair value adjustments [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Southern Company [Member] | PPA fair value adjustments [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	20 years
Southern Power [Member]
Goodwill [Line Items]
Goodwill	$ 2,000,000	2,000,000
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - accumulated amortization	(28,000,000)	(22,000,000)
Southern Power [Member] | PPA fair value adjustments [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangibles subject to amortization - accumulated amortization	(28,000,000)	(22,000,000)
Other intangibles subject to amortization - net	$ 428,000,000	434,000,000
Southern Power [Member] | PPA fair value adjustments [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Southern Power [Member] | PPA fair value adjustments [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	20 years
Southern Company Gas [Member]
Goodwill [Line Items]
Goodwill	$ 5,967,000,000	5,967,000,000
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	400,000,000	400,000,000
Other intangibles subject to amortization - accumulated amortization	(60,000,000)	(34,000,000)
Other intangibles subject to amortization - net	340,000,000	366,000,000
Total other intangible assets - net	340,000,000	366,000,000
Southern Company Gas [Member] | Gas Distribution Operations [Member]
Goodwill [Line Items]
Goodwill	4,702,000,000	4,702,000,000
Southern Company Gas [Member] | Gas Marketing Services [Member]
Goodwill [Line Items]
Goodwill	1,265,000,000	1,265,000,000
Southern Company Gas [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	221,000,000	221,000,000
Other intangibles subject to amortization - accumulated amortization	(41,000,000)	(30,000,000)
Other intangibles subject to amortization - net	$ 180,000,000	191,000,000
Southern Company Gas [Member] | Customer Relationships [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	11 years
Southern Company Gas [Member] | Customer Relationships [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	16 years
Southern Company Gas [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 115,000,000	115,000,000
Other intangibles subject to amortization - accumulated amortization	(4,000,000)	(2,000,000)
Other intangibles subject to amortization - net	$ 111,000,000	113,000,000
Southern Company Gas [Member] | Trade Names [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Southern Company Gas [Member] | Trade Names [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	28 years
Southern Company Gas [Member] | Storage and transportation contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 64,000,000	64,000,000
Other intangibles subject to amortization - accumulated amortization	(15,000,000)	(2,000,000)
Other intangibles subject to amortization - net	$ 49,000,000	$ 62,000,000
Southern Company Gas [Member] | Storage and transportation contracts [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	1 year
Southern Company Gas [Member] | Storage and transportation contracts [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	5 years