Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in fair value of qualifying hedges, tax	$ (8)	$ (6)	$ 0
Reclassification adjustment for amounts of qualifying hedges included in net income, tax	4	3	5
Change in fair value of marketable securities, tax	0	0	(2)
Benefit plan net gain (loss), tax	(1)	(32)	22
Reclassification adjustment for amounts of pension and other post retirement benefit plans included in net income, tax	4	2	4
Alabama Power [Member]
Changes in fair value of qualifying hedges, tax	(3)	(3)	0
Reclassification adjustment for amounts of qualifying hedges included in net income, tax	1	1	1
Georgia Power [Member]
Changes in fair value of qualifying hedges, tax	(6)	(3)	0
Reclassification adjustment for amounts of qualifying hedges included in net income, tax	1	1	1
Gulf Power [Member]
Changes in fair value of qualifying hedges, tax	0	0	0
Reclassification adjustment for amounts of qualifying hedges included in net income, tax	0	0	0
Mississippi Power [Member]
Reclassification adjustment for amounts of qualifying hedges included in net income, tax	1	1	1
Southern Power [Member]
Reclassification adjustment for amounts of qualifying hedges included in net income, tax	$ 0	$ 0	$ 2

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=36458714&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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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=36458714&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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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
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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
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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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