Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Millions		Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Preferred and Preference Stock of Subsidiaries	Noncontrolling Interests	ALABAMA POWER CO	ALABAMA POWER CO Common Stock	ALABAMA POWER CO Paid-In Capital	ALABAMA POWER CO Retained Earnings	ALABAMA POWER CO Accumulated Other Comprehensive Income (Loss)	GEORGIA POWER CO	GEORGIA POWER CO Common Stock	GEORGIA POWER CO Paid-In Capital	GEORGIA POWER CO Retained Earnings	GEORGIA POWER CO Accumulated Other Comprehensive Income (Loss)	GULF POWER CO	GULF POWER CO Common Stock	GULF POWER CO Paid-In Capital	GULF POWER CO Retained Earnings	GULF POWER CO Accumulated Other Comprehensive Income (Loss)	MISSISSIPPI POWER CO	MISSISSIPPI POWER CO Common Stock	MISSISSIPPI POWER CO Paid-In Capital	MISSISSIPPI POWER CO Retained Earnings	MISSISSIPPI POWER CO Accumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CO	SOUTHERN POWER CO Common Stock	SOUTHERN POWER CO Paid-In Capital	SOUTHERN POWER CO Retained Earnings	SOUTHERN POWER CO Accumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CO Total Common Stockholder's Equity	SOUTHERN POWER CO Noncontrolling Interests	[1]	SOUTHERN Co GAS	SOUTHERN Co GAS Common Stock	SOUTHERN Co GAS Treasury	SOUTHERN Co GAS Paid-In Capital	SOUTHERN Co GAS Retained Earnings	SOUTHERN Co GAS Accumulated Other Comprehensive Income (Loss)	SOUTHERN Co GAS Noncontrolling Interests
Beginning balance (in shares) (Predecessor) at Dec. 31, 2014																																							119,647	217
Beginning balance (in shares) at Dec. 31, 2014			908,502	725							31,000					9,000					5,000					1,000					0
Beginning balance (Predecessor) at Dec. 31, 2014																																						$ 3,828	$ 599	$ (8)	$ 2,087	$ 1,312	$ (206)	$ 44
Beginning balance at Dec. 31, 2014		$ 20,926	$ 4,539	$ (26)	$ 5,955	$ 9,609	$ (128)	$ 756	$ 221	$ 5,752	$ 1,222	$ 2,304	$ 2,255	$ (29)	$ 10,421	$ 398	$ 6,196	$ 3,835	$ (8)	$ 1,309	$ 483	$ 560	$ 267	$ (1)	$ 2,084	$ 38	$ 2,612	$ (559)	$ (7)	$ 1,971	$ 0	$ 1,176	$ 573	$ 3	$ 1,752	$ 219
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income after dividends on preferred and preference stock | Predecessor																																						353				353
Net income after dividends on preferred and preference stock		2,367				2,367				785			785		1,260			1,260		148			148		(8)			(8)
Net income attributable to Southern Power Company																														215			215		215
Other comprehensive income (loss) | Predecessor																																						20					20	0
Other comprehensive income (loss)		(2)					(2)			(3)				(3)	(7)				(7)	1				1	1				1	1				1	1
Stock issued (in shares) | Predecessor																																							221
Stock issued (in shares)			6,571	2,599																	1,000
Stock issued | Predecessor																																						12	$ 1		11
Stock issued		256	$ 33		223															20	$ 20
Stock-based compensation (in shares) | Predecessor																																							509
Stock-based compensation | Predecessor																																						4	$ 3		1
Stock-based compensation		100			100
Stock repurchased, at cost		(115)		$ (115)
Cash dividends on common stock | Predecessor																																						(244)				(244)
Cash dividends on common stock		(1,959)				(1,959)				(571)			(571)		(1,034)			(1,034)		(130)			(130)							(131)			(131)		(131)
Preference stock redemption		(150)						(150)
Contributions from noncontrolling interests		567							567																					567						567
Distributions to noncontrolling interests | Predecessor																																						(18)						(18)
Distributions to noncontrolling interests		(18)							(18)																					(17)						(17)
Purchase of membership interests from noncontrolling interests																														0
Net income attributable to noncontrolling interests | Predecessor																																						20						20
Net income attributable to noncontrolling interests		12							12																					12						12
Other (in shares)				(28)
Other		(2)		$ (1)	4	(7)		3	(1)	(8)			(8)												1			1
Capital contributions from parent company										37		37			79		79			7		7			281		281			646		646			646
Ending balance (in shares) (Predecessor) at Dec. 31, 2015																																							120,377	217
Ending balance (in shares) at Dec. 31, 2015			915,073	3,352							31,000					9,000					6,000					1,000					0
Ending balance (Predecessor) at Dec. 31, 2015																																						3,975	$ 603	$ (8)	2,099	1,421	(186)	46
Ending balance at Dec. 31, 2015		21,982	$ 4,572	$ (142)	6,282	10,010	(130)	609	781	5,992	$ 1,222	2,341	2,461	(32)	10,719	$ 398	6,275	4,061	(15)	1,355	$ 503	567	285	0	2,359	$ 38	2,893	(566)	(6)	3,264	$ 0	1,822	657	4	2,483	781
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income after dividends on preferred and preference stock | Predecessor																																						131				131
Other comprehensive income (loss) | Predecessor																																						(35)					(35)
Stock issued (in shares) | Predecessor																																							95
Stock issued | Predecessor																																						6	$ 0		6
Stock-based compensation (in shares) | Predecessor																																							270
Stock-based compensation | Predecessor																																						30	$ 2		28
Cash dividends on common stock | Predecessor																																						(128)				(128)
Reclassification from redeemable noncontrolling interests | Predecessor																																						(46)						(46)
Ending balance (in shares) (Predecessor) at Jun. 30, 2016																																							120,742	217
Ending balance (Predecessor) at Jun. 30, 2016																																						3,933	$ 605	$ (8)	2,133	1,424	(221)	0
Ending balance at Jun. 30, 2016		8,001
Beginning balance (in shares) (Predecessor) at Dec. 31, 2015																																							120,377	217
Beginning balance (in shares) at Dec. 31, 2015			915,073	3,352							31,000					9,000					6,000					1,000					0
Beginning balance (Predecessor) at Dec. 31, 2015																																						3,975	$ 603	$ (8)	2,099	1,421	(186)	46
Beginning balance at Dec. 31, 2015		21,982	$ 4,572	$ (142)	6,282	10,010	(130)	609	781	5,992	$ 1,222	2,341	2,461	(32)	10,719	$ 398	6,275	4,061	(15)	1,355	$ 503	567	285	0	2,359	$ 38	2,893	(566)	(6)	3,264	$ 0	1,822	657	4	2,483	781
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income after dividends on preferred and preference stock		2,448				2,448				822			822		1,330			1,330		131			131		(50)			(50)
Net income attributable to Southern Power Company																														338			338		338
Other comprehensive income (loss)		(50)					(50)			2				2	2				2	1				1	2				2	31				31	31
Stock issued (in shares)			76,140	2,599
Stock issued		3,758	$ 380	$ 115	3,263
Stock-based compensation		120			120
Cash dividends on common stock		(2,104)				(2,104)				(765)			(765)		(1,305)			(1,305)		(120)			(120)							(272)			(272)		(272)
Contributions from noncontrolling interests		618							618																					618						618
Distributions to noncontrolling interests		(57)							(57)																					(57)						(57)
Purchase of membership interests from noncontrolling interests		(129)							(129)																					(129)						(129)
Net income attributable to noncontrolling interests		32							32																					32						32
Other (in shares)				(66)
Other		(6)		$ (4)	(4)	2																										(1)	1
Capital contributions from parent company										272		272			610		610			22		22			632		632			1,850		1,850			1,850
Ending balance (in shares) at Dec. 31, 2016			991,213	819							31,000					9,000					6,000					1,000					0								0	0
Ending balance at Dec. 31, 2016		26,612	$ 4,952	$ (31)	9,661	10,356	(180)	609	1,245	6,323	$ 1,222	2,613	2,518	(30)	11,356	$ 398	6,885	4,086	(13)	1,389	$ 503	589	296	1	2,943	$ 38	3,525	(616)	(4)	5,675	$ 0	3,671	724	35	4,430	1,245		9,109	$ 0	$ 0	9,095	(12)	26	0
Beginning balance (in shares) (Predecessor) at Jun. 30, 2016																																							120,742	217
Beginning balance (Predecessor) at Jun. 30, 2016																																						3,933	$ 605	$ (8)	2,133	1,424	(221)	0
Beginning balance at Jun. 30, 2016		8,001
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income after dividends on preferred and preference stock																																						114				114
Other comprehensive income (loss)																																						26					26
Cash dividends on common stock																																						(126)				(126)
Capital contributions from parent company																																						1,094			1,094
Ending balance (in shares) at Dec. 31, 2016			991,213	819							31,000					9,000					6,000					1,000					0								0	0
Ending balance at Dec. 31, 2016		26,612	$ 4,952	$ (31)	9,661	10,356	(180)	609	1,245	6,323	$ 1,222	2,613	2,518	(30)	11,356	$ 398	6,885	4,086	(13)	1,389	$ 503	589	296	1	2,943	$ 38	3,525	(616)	(4)	5,675	$ 0	3,671	724	35	4,430	1,245		9,109	$ 0	$ 0	9,095	(12)	26	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income after dividends on preferred and preference stock		842				842				848			848		1,414			1,414		135			135		(2,590)			(2,590)										243				243
Net income attributable to Southern Power Company																														1,071			1,071		1,071
Other comprehensive income (loss)		(9)					(9)			4				4	3				3	(1)				(1)						(10)				(10)	(10)			(5)					(5)
Stock issued (in shares)			17,319	0																	0
Stock issued		793	$ 86	$ 0	707															175	$ 175
Stock-based compensation		105			105
Cash dividends on common stock		(2,300)				(2,300)				(714)			(714)		(1,281)			(1,281)		(165)			(165)							(317)			(317)		(317)			(443)				(443)
Other Comprehensive Income (Loss), Transfer from Service Company	[2]																													(27)				(27)	(27)
Preference stock redemption		(609)						(609)
Contributions from noncontrolling interests		79							79																					79						79
Distributions to noncontrolling interests		(122)							(122)																					(122)						(122)
Net income attributable to noncontrolling interests		44							44																					44						44
Reclassification from redeemable noncontrolling interests																														114						114
Reclassification from redeemable noncontrolling interests		114							114
Other (in shares)				(110)
Other		(21)		$ (5)	(4)	(13)			1	(5)			(5)		(4)			(4)		(7)			(7)		1			1		(7)		(7)	0		(7)	0		1			2	0	(1)
Capital contributions from parent company										373		373			443		443			5		5			1,004		1,004			(2)		(2)			(2)			117			117
Ending balance (in shares) at Dec. 31, 2017			1,008,532	929							31,000					9,000					6,000					1,000					0								0	0
Ending balance at Dec. 31, 2017		$ 25,528	$ 5,038	$ (36)	$ 10,469	$ 8,885	$ (189)	$ 0	$ 1,361	$ 6,829	$ 1,222	$ 2,986	$ 2,647	$ (26)	$ 11,931	$ 398	$ 7,328	$ 4,215	$ (10)	$ 1,531	$ 678	$ 594	$ 259	$ 0	$ 1,358	$ 38	$ 4,529	$ (3,205)	$ (4)	$ 6,498	$ 0	$ 3,662	$ 1,478	$ (2)	$ 5,138	$ 1,360		$ 9,022	$ 0	$ 0	$ 9,214	$ (212)	$ 20	$ 0

[1] Excludes redeemable noncontrolling interests. See Note 10 to the financial statements under "Noncontrolling Interests" for additional information.

[2] Amount includes carry-over OCI balance of $27 million in connection with the Company becoming a participant to the Southern Company qualified pension plan.