Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Qualifying hedges change in fair value tax			$ (84)	$ (8)	$ (6)
Qualifying hedges reclassification adjustment tax			43	4	3
Pension and other postretirement benefit plans gain (loss) tax			10	(1)	(32)
Pension and other postretirement benefit plans reclassification adjustment tax			3	4	2
Alabama Power [Member]
Qualifying hedges change in fair value tax			(1)	(3)	(3)
Qualifying hedges reclassification adjustment tax			2	1	1
Georgia Power [Member]
Qualifying hedges change in fair value tax			0	(6)	(3)
Qualifying hedges reclassification adjustment tax			2	1	1
Gulf Power [Member]
Qualifying hedges change in fair value tax			0	0	0
Mississippi Power [Member]
Qualifying hedges change in fair value tax			1	0	0
Qualifying hedges reclassification adjustment tax			1	1	1
Southern Power [Member]
Qualifying hedges change in fair value tax			(17)	0	0
Qualifying hedges reclassification adjustment tax			$ 36	0	0
Successor [Member] \| Southern Company Gas [Member]
Qualifying hedges change in fair value tax	$ (1)
Qualifying hedges reclassification adjustment tax	0
Pension and other postretirement benefit plans gain (loss) tax	19
Pension and other postretirement benefit plans reclassification adjustment tax	$ 0
Predecessor [Member] \| Southern Company Gas [Member]
Qualifying hedges change in fair value tax		$ (23)		(3)	(2)
Qualifying hedges reclassification adjustment tax		0		1	(2)
Pension and other postretirement benefit plans gain (loss) tax		0		0	(48)
Pension and other postretirement benefit plans reclassification adjustment tax		$ 4		$ 9	$ 5

Amount of tax expense (benefit) related to (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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
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-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580

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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).

+ 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
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-SubTopic 10
-Section 50
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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
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-Topic 220
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-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

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