Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	ALABAMA POWER CO	ALABAMA POWER CO Common Stock	ALABAMA POWER CO Paid-In Capital	ALABAMA POWER CO Retained Earnings (Accumulated Deficit)	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 (Accumulated Deficit)	GEORGIA 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 (Accumulated Deficit)	MISSISSIPPI POWER CO Accumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CO	SOUTHERN POWER CO Total Common Stockholders' Equity	SOUTHERN POWER CO Paid-In Capital	SOUTHERN POWER CO Retained Earnings (Accumulated Deficit)	SOUTHERN POWER CO Accumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CO Noncontrolling Interests	SOUTHERN Co GAS	SOUTHERN Co GAS Paid-In Capital	SOUTHERN Co GAS Retained Earnings (Accumulated Deficit)	SOUTHERN Co GAS Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2018		1,035	1						31					9					1
Beginning balance at Dec. 31, 2018	$ 29,039	$ 5,164	$ (38)	$ 11,094	$ 8,706	$ (203)	$ 4,316	$ 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	$ 2,968	$ 1,600	$ 1,352	$ 16	$ 4,316	$ 8,570	$ 8,856	$ (312)	$ 26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,055				2,084		(29)
Net income (loss)													311			311		37			37		27	56		56		(29)	270		270
Net income								217			217
Return of capital to parent company																		(38)		(38)
Capital contributions from parent company								1,236		1,236			29		29			2		2			1	1	1				17	17
Other comprehensive income (loss)								1				1	1				1						(4)	(4)			(4)		(1)			(1)
Stock issued (in shares)		6
Stock issued	224	$ 28		196
Stock-based compensation	24			24
Cash dividends on common stock	(623)				(623)			(211)			(211)		(394)			(394)							(51)	(51)		(51)			(118)		(118)
Contributions from noncontrolling interests	3						3																3					3
Distributions to noncontrolling interests	(41)						(41)																(41)					(41)
Other	6		$ (2)	7			1						(1)		(1)								(1)	(2)	(1)	(1)		1
Ending balance (in shares) at Mar. 31, 2019		1,041	1						31					9					1
Ending balance at Mar. 31, 2019	30,687	$ 5,192	$ (40)	11,321	10,167	(203)	4,250	8,720	$ 1,222	4,744	2,781	(27)	14,269	$ 398	10,350	3,529	(8)	1,610	$ 38	4,510	(2,934)	(4)	7,218	2,968	1,600	1,356	12	4,250	8,738	8,873	(160)	25
Beginning balance (in shares) at Dec. 31, 2018		1,035	1						31					9					1
Beginning balance at Dec. 31, 2018	29,039	$ 5,164	$ (38)	11,094	8,706	(203)	4,316	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	2,968	1,600	1,352	16	4,316	8,570	8,856	(312)	26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,989							520					759					74					230						376
Net income	2,982							513															230						376
Ending balance (in shares) at Jun. 30, 2019		1,046	1						31					9					1
Ending balance at Jun. 30, 2019	31,131	$ 5,217	$ (41)	11,540	10,420	(238)	4,233	8,829	$ 1,222	4,767	2,866	(26)	14,316	$ 398	10,371	3,582	(35)	1,617	$ 38	4,480	(2,897)	(4)	6,818	2,585	1,102	1,479	4	4,233	8,759	8,908	(171)	22
Beginning balance (in shares) at Mar. 31, 2019		1,041	1						31					9					1
Beginning balance at Mar. 31, 2019	30,687	$ 5,192	$ (40)	11,321	10,167	(203)	4,250	8,720	$ 1,222	4,744	2,781	(27)	14,269	$ 398	10,350	3,529	(8)	1,610	$ 38	4,510	(2,934)	(4)	7,218	2,968	1,600	1,356	12	4,250	8,738	8,873	(160)	25
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	928				899		29
Net income (loss)	931							299					448			448		37			37		203	174		174		29	106		106
Net income	899							296			296												174						106
Return of capital to parent company																		(38)		(38)			(505)	(505)	(505)
Capital contributions from parent company								23		23			20		20			8		8			7	7	7				35	35
Other comprehensive income (loss)	(35)					(35)		1				1	(27)				(27)						(8)	(8)			(8)		(3)			(3)
Stock issued (in shares)		5
Stock issued	228	$ 25		203
Stock-based compensation	11			11
Cash dividends on common stock	(646)				(646)			(211)			(211)		(394)			(394)							(52)	(52)		(52)			(117)		(117)
Contributions from noncontrolling interests	2						2																2					2
Distributions to noncontrolling interests	(47)						(47)																(47)					(47)
Other	3		$ (1)	5			(1)						0		1	(1)							0	1		1		(1)
Ending balance (in shares) at Jun. 30, 2019		1,046	1						31					9					1
Ending balance at Jun. 30, 2019	31,131	$ 5,217	$ (41)	11,540	10,420	(238)	4,233	8,829	$ 1,222	4,767	2,866	(26)	14,316	$ 398	10,371	3,582	(35)	1,617	$ 38	4,480	(2,897)	(4)	6,818	2,585	1,102	1,479	4	4,233	8,759	8,908	(171)	22
Beginning balance (in shares) at Dec. 31, 2019		1,054	1						31					9					1
Beginning balance at Dec. 31, 2019	31,759	$ 5,257	$ (42)	11,734	10,877	(321)	4,254	8,955	$ 1,222	4,755	3,001	(23)	15,065	$ 398	10,962	3,756	(51)	1,652	$ 38	4,449	(2,832)	(3)	6,622	2,368	909	1,485	(26)	4,254	9,506	9,697	(198)	7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	837				868		(31)
Net income (loss)													331			331		32			32		44	75		75		(31)	275		275
Net income								280			280
Return of capital to parent company																		(37)		(37)									(2)	(2)
Capital contributions from parent company								612		612			502		502			76		76
Other comprehensive income (loss)	(47)					(47)		1				1	(1)				(1)						(33)	(33)			(33)		(15)			(15)
Stock issued (in shares)		3
Stock issued	52	$ 9		43
Stock-based compensation	5			5
Cash dividends on common stock	(655)				(655)			(239)			(239)		(385)			(385)							(50)	(50)		(50)			(133)		(133)
Contributions from noncontrolling interests	16						16																16					16
Distributions to noncontrolling interests	(48)						(48)																(48)					(48)
Other	(3)		$ (2)		(2)	1												(1)		(1)
Ending balance (in shares) at Mar. 31, 2020		1,057	1						31					9					1
Ending balance at Mar. 31, 2020	31,916	$ 5,266	$ (44)	11,782	11,088	(367)	4,191	9,609	$ 1,222	5,367	3,042	(22)	15,512	$ 398	11,464	3,702	(52)	1,722	$ 38	4,487	(2,800)	(3)	6,551	2,360	909	1,510	(59)	4,191	9,631	9,695	(56)	(8)
Beginning balance (in shares) at Dec. 31, 2019		1,054	1						31					9					1
Beginning balance at Dec. 31, 2019	31,759	$ 5,257	$ (42)	11,734	10,877	(321)	4,254	8,955	$ 1,222	4,755	3,001	(23)	15,065	$ 398	10,962	3,756	(51)	1,652	$ 38	4,449	(2,832)	(3)	6,622	2,368	909	1,485	(26)	4,254	9,506	9,697	(198)	7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,461							585					638					71					112						346
Net income	1,480							578															138						346
Ending balance (in shares) at Jun. 30, 2020		1,057	1						31					9					1
Ending balance at Jun. 30, 2020	31,961	$ 5,266	$ (44)	11,787	11,024	(363)	4,291	9,670	$ 1,222	5,368	3,101	(21)	15,437	$ 398	11,465	3,624	(50)	1,724	$ 38	4,450	(2,761)	(3)	6,659	2,368	907	1,523	(62)	4,291	9,769	9,895	(118)	(8)
Beginning balance (in shares) at Mar. 31, 2020		1,057	1						31					9					1
Beginning balance at Mar. 31, 2020	31,916	$ 5,266	$ (44)	11,782	11,088	(367)	4,191	9,609	$ 1,222	5,367	3,042	(22)	15,512	$ 398	11,464	3,702	(52)	1,722	$ 38	4,487	(2,800)	(3)	6,551	2,360	909	1,510	(59)	4,191	9,631	9,695	(56)	(8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	617				612		5
Net income (loss)	621							302					308			308		39			39		68	63		63		5	71		71
Net income	612							298			298												63						71
Return of capital to parent company																		(37)		(37)
Capital contributions from parent company								1		1			1		1														200	200
Other comprehensive income (loss)	4					4		1				1	2				2						(3)	(3)			(3)
Stock issued	7			7
Stock-based compensation	11			11
Cash dividends on common stock	(677)				(677)			(239)			(239)		(386)			(386)							(50)	(50)		(50)			(133)		(133)
Contributions from noncontrolling interests	165						165																165					165
Distributions to noncontrolling interests	(70)						(70)																(70)					(70)
Other	(12)			(13)	1																		(2)	(2)	(2)	0	0	0
Ending balance (in shares) at Jun. 30, 2020		1,057	1						31					9					1
Ending balance at Jun. 30, 2020	$ 31,961	$ 5,266	$ (44)	$ 11,787	$ 11,024	$ (363)	$ 4,291	$ 9,670	$ 1,222	$ 5,368	$ 3,101	$ (21)	$ 15,437	$ 398	$ 11,465	$ 3,624	$ (50)	$ 1,724	$ 38	$ 4,450	$ (2,761)	$ (3)	$ 6,659	$ 2,368	$ 907	$ 1,523	$ (62)	$ 4,291	$ 9,769	$ 9,895	$ (118)	$ (8)