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	Alabama Power Common Stock	Alabama Power Paid-In Capital	Alabama Power Retained Earnings	Alabama Power Accumulated Other Comprehensive Income (Loss)	Georgia Power	Georgia Power Common Stock	Georgia Power Paid-In Capital	Georgia Power Retained Earnings	Georgia Power Accumulated Other Comprehensive Income (Loss)	Mississippi Power	Mississippi Power Common Stock	Mississippi Power Paid-In Capital	Mississippi Power Retained Earnings	Mississippi Power Accumulated Other Comprehensive Income (Loss)	Southern Power		Southern Power Common Stock	Southern Power Paid-In Capital		Southern Power Retained Earnings	Southern Power Accumulated Other Comprehensive Income (Loss)	Southern Power Total Common Stockholder's Equity		Southern Power Noncontrolling Interests	[1]	Southern Company Gas	Southern Company Gas Common Stock	Southern Company Gas Treasury	Southern Company Gas Paid-In Capital	Southern Company Gas Retained Earnings	Southern Company Gas Accumulated Other Comprehensive Income (Loss)	Southern Company Gas Noncontrolling Interests
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					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	[1]	$ 5,992	$ 1,222	$ 2,341	$ 2,461	$ (32)	$ 10,719	$ 398	$ 6,275	$ 4,061	$ (15)	$ 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 (loss) after dividends on preferred and preference stock | Predecessor																																					131				131
Return of capital | Predecessor																																					0
Other comprehensive income (loss) | Predecessor																																					(35)					(35)
Stock issued (in shares) | Predecessor																																						95
Stock issued | Predecessor																																					6			6
Stock-based compensation (in shares) | Predecessor																																						270
Stock-based compensation | Predecessor																																					30	$ 2		28
Cash dividends on common stock | Predecessor																																					(128)				(128)
Reclassification of noncontrolling interest | Predecessor																																					(46)						(46)
Ending balance (in shares) (Predecessor) at Jun. 30, 2016																																						120,742	217
Ending balance (in shares) at Jun. 30, 2016																																						0	0
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	$ 0	$ 0	8,001	0	0	0
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					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	[1]	5,992	$ 1,222	2,341	2,461	(32)	10,719	$ 398	6,275	4,061	(15)	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 (loss) after dividends on preferred and preference stock		2,448				2,448					822			822		1,330			1,330		(50)			(50)		338					338		338
Return of capital																										0
Capital contributions from (to) parent company											272		272			610		610			632		632			1,850			1,850				1,850
Other comprehensive income (loss)		(50)					(50)				2				2	2				2	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)							(272)					(272)		(272)
Contributions from noncontrolling interests		618							618	[1]																618									618
Distributions to noncontrolling interests		(57)							(57)	[1]																(57)									(57)
Purchase of membership interests from noncontrolling interests		(129)							(129)	[1]																(129)									(129)
Net income attributable to noncontrolling interests		(32)							(32)	[1]																32									32
Other (in shares)				(66)
Other		(6)		$ (4)	(4)	2																				0			(1)		1
Ending balance (in shares) at Dec. 31, 2016			991,213	819								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2016		26,612	$ 4,952	$ (31)	9,661	10,356	(180)	609	1,245	[1]	6,323	$ 1,222	2,613	2,518	(30)	11,356	$ 398	6,885	4,086	(13)	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 (in shares) at Jun. 30, 2016																																						0	0
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	$ 0	$ 0	8,001	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) after dividends on preferred and preference stock																																					114				114
Return of capital																																					0
Capital contributions from (to) parent company																																					1,094			1,094
Other comprehensive income (loss)																																					26					26
Cash dividends on common stock																																					(126)				(126)
Ending balance (in shares) at Dec. 31, 2016			991,213	819								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2016		26,612	$ 4,952	$ (31)	9,661	10,356	(180)	609	1,245	[1]	6,323	$ 1,222	2,613	2,518	(30)	11,356	$ 398	6,885	4,086	(13)	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 (loss) after dividends on preferred and preference stock		842				842					848			848		1,414			1,414		(2,590)			(2,590)		1,071					1,071		1,071				243				243
Return of capital																										0											0
Capital contributions from (to) parent company											373		373			443		443			1,004		1,004			(2)			(2)				(2)				117			117
Other comprehensive income (loss)		(9)					(9)				4				4	3				3						(10)						(10)	(10)				(5)					(5)
Stock issued (in shares)			17,319
Stock issued		793	$ 86		707
Stock-based compensation		105			105
Cash dividends on common stock		(2,300)				(2,300)					(714)			(714)		(1,281)			(1,281)							(317)					(317)		(317)				(443)				(443)
Other comprehensive income transfer from SCS	[2]																									(27)						(27)	(27)
Preference stock redemption		(609)						(609)
Contributions from noncontrolling interests		79							79	[1]																79									79
Distributions to noncontrolling interests		(122)							(122)	[1]																(122)									(122)
Purchase of membership interests from noncontrolling interests																										(59)
Net income attributable to noncontrolling interests		(44)							(44)	[1]																44									44
Reclassification from redeemable noncontrolling interests		114							114	[1]																114									114
Other (in shares)				(110)
Other		(21)		$ (5)	(4)	(13)			1	[1]	(5)			(5)		(4)			(4)		1			1		(7)			(7)				(7)				1			2		(1)
Ending balance (in shares) at Dec. 31, 2017			1,008,532	929								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2017		25,528	$ 5,038	$ (36)	10,469	8,885	(189)	0	1,361	[1]	6,829	$ 1,222	2,986	2,647	(26)	11,931	$ 398	7,328	4,215	(10)	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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) after dividends on preferred and preference stock		2,226				2,226					930			930		793			793		235			235		187					187		187				372				372
Return of capital																										(1,650)			(1,650)				(1,650)				(400)			(400)
Capital contributions from (to) parent company											522		522			2,994		2,994			17		17			2			2				2				42			42
Other comprehensive income (loss)		26					26				4				4	3				3						14						14	14				2					2
Stock issued (in shares)			26,209
Stock issued		1,090	$ 126		964
Stock-based compensation		84			84
Cash dividends on common stock		(2,425)				(2,425)					(801)			(801)		(1,396)			(1,396)							(312)					(312)		(312)				(468)				(468)
Contributions from noncontrolling interests		1,372							1,372	[1]																1,372									1,372
Distributions to noncontrolling interests		(164)							(164)	[1]																(164)									(164)
Net income attributable to noncontrolling interests		(58)							(58)	[1]																59									59
Sale of noncontrolling interests		1,273			(417)				1,690																	1,273	[3]		(417)	[3]			(417)	[3]	1,690	[3]
Other (in shares)				(24)
Other		(29)		$ (2)	(6)	20	(40)		(1)	[1]	(7)			(1)	(6)	(2)				(2)	(1)			(1)		5			3		(1)	4	6		(1)		0				(4)	4
Ending balance (in shares) at Dec. 31, 2018			1,034,741	953								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2018		$ 29,039	$ 5,164	$ (38)	$ 11,094	$ 8,706	$ (203)	$ 0	$ 4,316	[1]	$ 7,477	$ 1,222	$ 3,508	$ 2,775	$ (28)	$ 14,323	$ 398	$ 10,322	$ 3,612	$ (9)	$ 1,609	$ 38	$ 4,546	$ (2,971)	$ (4)	$ 7,284		$ 0	$ 1,600		$ 1,352	$ 16	$ 2,968		$ 4,316		$ 8,570	$ 0	$ 0	$ 8,856	$ (312)	$ 26	$ 0

[1] Excludes redeemable noncontrolling interests. See Note 7 to the financial statements under "Noncontrolling Interests" for additional information.

[2] In connection with Southern Power becoming a participant to the Southern Company qualified pension plan and other postretirement benefit plan, $27 million of other comprehensive income, net of tax of $9 million, was transferred from SCS.

[3] See Note 15 under "Southern Power - Sales of Renewable Facility Interests" for additional information.