Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in fair value, tax	$ 15	$ 12		$ 32	$ (74)
Reclassification adjustment for qualified hedges, tax	(10)	2		(36)	13
Reclassification adjustment for pension and other post retirement benefit plans, tax	1	1		2	2
ALABAMA POWER CO
Changes in fair value, tax	0	0		0	(1)
Reclassification adjustment for qualified hedges, tax	1	1		2	2
GEORGIA POWER CO
Reclassification adjustment for qualified hedges, tax	0	0		1	1
GULF POWER CO
Changes in fair value, tax	0	0		(1)	(3)
MISSISSIPPI POWER CO
Changes in fair value, tax	0	0		0	0
Reclassification adjustment for qualified hedges, tax	0	0		0	0
SOUTHERN POWER CO
Changes in fair value, tax	15	14		35	(1)
Reclassification adjustment for qualified hedges, tax	(12)	(1)		(42)	$ 7
SOUTHERN Co GAS
Changes in fair value, tax	0	(2)		(2)
Reclassification adjustment for qualified hedges, tax	0	0		0
Reclassification adjustment for pension and other post retirement benefit plans, tax	$ 0	$ 0		$ (1)
Predecessor \| SOUTHERN Co GAS
Changes in fair value, tax			$ (23)
Reclassification adjustment for qualified hedges, tax			0
Reclassification adjustment for pension and other post retirement benefit plans, tax			$ 4

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=84228862&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=84234895&loc=d3e41638-113959

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

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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=84228862&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=84228862&loc=SL7669646-108580

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