Condensed Consolidated Statements of Income (Unaudited) - Parenthetical - Southern Company Gas [Member] - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Excise taxes collected	$ 48
Predecessor [Member]
Excise taxes collected		$ 40

The excise taxes collected by a public utility and reported in revenues if the amount of excise taxes is equal to 1 percent or more of such total.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(1)(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_ExciseTaxesCollected
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration