Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($)	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Changes in fair value, tax	$ (5,000,000)	$ (72,000,000)
Reclassification adjustment for qualified hedges, tax	(1,000,000)	1,000,000
Reclassification adjustment for pension and other post retirement benefit plans, tax	0	1,000,000
Alabama Power [Member]
Changes in fair value, tax	0	(1,000,000)
Reclassification adjustment for qualified hedges, tax	1,000,000	1,000,000
Georgia Power [Member]
Changes in fair value, tax	0	0
Reclassification adjustment for qualified hedges, tax	0	0
Gulf Power [Member]
Changes in fair value, tax	0	(2,000,000)
Mississippi Power [Member]
Changes in fair value, tax	0	0
Southern Power [Member]
Changes in fair value, tax	(4,000,000)	0
Reclassification adjustment for qualified hedges, tax	(3,000,000)	0
Southern Company Gas [Member]
Changes in fair value, tax	(1,000,000)
Reclassification adjustment for qualified hedges, tax	0
Reclassification adjustment for pension and other post retirement benefit plans, tax	$ (1,000,000)
Predecessor [Member] \| Southern Company Gas [Member]
Changes in fair value, tax		(16,000,000)
Reclassification adjustment for qualified hedges, tax		0
Reclassification adjustment for pension and other post retirement benefit plans, tax		$ 2,000,000

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph c
-URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41638-113959

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e689-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580

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Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580

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