Introduction - Intangibles, Amortization (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 957,000,000	$ 957,000,000
Other intangible assets, accumulated amortization	97,000,000	62,000,000
Other intangibles subject to amortization - net	860,000,000	895,000,000
Other intangible assets, net of amortization	935,000,000	970,000,000
Total other intangible assets - gross	1,032,000,000	1,032,000,000
Amortization of intangible assets	35,000,000
Southern Power [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	28,000,000	22,000,000
Amortization of intangible assets	6,000,000
Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	400,000,000	400,000,000
Other intangible assets, accumulated amortization	60,000,000	34,000,000
Other intangibles subject to amortization - net	340,000,000	366,000,000
Other intangible assets, net of amortization	340,000,000	366,000,000
Amortization of intangible assets	26,000,000
Customer Relationships [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	268,000,000	268,000,000
Other intangible assets, accumulated amortization	44,000,000	32,000,000
Other intangibles subject to amortization - net	224,000,000	236,000,000
Customer Relationships [Member] | Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	221,000,000	221,000,000
Other intangible assets, accumulated amortization	41,000,000	30,000,000
Other intangibles subject to amortization - net	180,000,000	191,000,000
Trade Names [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	158,000,000	158,000,000
Other intangible assets, accumulated amortization	8,000,000	5,000,000
Other intangibles subject to amortization - net	150,000,000	153,000,000
Trade Names [Member] | Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	115,000,000	115,000,000
Other intangible assets, accumulated amortization	4,000,000	2,000,000
Other intangibles subject to amortization - net	111,000,000	113,000,000
Patents [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	4,000,000	4,000,000
Other intangible assets, accumulated amortization	0	0
Other intangibles subject to amortization - net	4,000,000	4,000,000
Backlog [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	5,000,000	5,000,000
Other intangible assets, accumulated amortization	1,000,000	1,000,000
Other intangibles subject to amortization - net	4,000,000	4,000,000
Storage and Transportation Contracts [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	64,000,000	64,000,000
Other intangible assets, accumulated amortization	15,000,000	2,000,000
Other intangibles subject to amortization - net	49,000,000	62,000,000
Storage and Transportation Contracts [Member] | Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	64,000,000	64,000,000
Other intangible assets, accumulated amortization	15,000,000	2,000,000
Other intangibles subject to amortization - net	49,000,000	62,000,000
Software and other [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	2,000,000	2,000,000
Other intangible assets, accumulated amortization	1,000,000	0
Other intangibles subject to amortization - net	1,000,000	2,000,000
PPA fair value adjustments [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangible assets, accumulated amortization	28,000,000	22,000,000
Other intangibles subject to amortization - net	428,000,000	434,000,000
PPA fair value adjustments [Member] | Southern Power [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangible assets, accumulated amortization	28,000,000	22,000,000
Other intangibles subject to amortization - net	428,000,000	434,000,000
FCC Licenses [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	$ 75,000,000	$ 75,000,000