Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions		Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	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 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	Southern Company Gas	Southern Company Gas Paid-In Capital	Southern Company Gas Retained Earnings	Southern Company Gas Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017			1,009	1						31					9					1
Beginning balance at Dec. 31, 2017		$ 25,528	$ 5,038	$ (36)	$ 10,469	$ 8,885	$ (189)	$ 1,361	$ 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	$ 3,662	$ 1,478	$ (2)	$ 5,138	$ 1,360	$ 9,022	$ 9,214	$ (212)	$ 20
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)		2,284				2,226		58
Net income after dividends on preferred stock		2,226							930			930							235			235		187						372		372
Net Income		2,300							945					793			793		236					246		187		187	59	372
Return of capital to parent company																								(1,650)	(1,650)			(1,650)		(400)	(400)
Capital contributions from 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
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																1,372					1,372
Distributions to noncontrolling interests		(164)						(164)																(164)					(164)
Sale of noncontrolling interests		1,273			(417)			1,690																1,273	(417)			(417)	1,690
Other		(29)		$ (2)	(6)	20	(40)	(1)	(7)			(1)	(6)	(2)				(2)	(1)			(1)		5	3	(1)	4	6	(1)	0	0	(4)	4
Ending balance (in shares) at Dec. 31, 2018			1,035	1						31					9					1
Ending 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	1,600	1,352	16	2,968	4,316	8,570	8,856	(312)	26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)		4,729				4,739		(10)
Net income after dividends on preferred stock		4,739							1,070			1,070							139			139		339						585		585
Net Income		4,744							1,085					1,720			1,720		139					329		339		339	(10)	585
Return of capital to parent company																			(150)		(150)			(755)	(755)			(755)
Capital contributions from parent company									1,247		1,247			640		640			53		53			64	64			64		841	841
Other comprehensive income (loss)		(118)					(118)		4				4	(42)				(42)	1				1	(42)			(42)	(42)		(19)			(19)
Issuance of equity units	[1]	(198)			(198)
Stock issued (in shares)			19
Stock issued		844	$ 93		751
Stock-based compensation		66			66
Cash dividends on common stock		(2,570)				(2,570)			(844)			(844)		(1,576)			(1,576)							(206)		(206)		(206)		(471)		(471)
Contributions from noncontrolling interests		276						276																276					276
Distributions to noncontrolling interests		(327)						(327)																(327)					(327)
Other		18		$ (4)	21	2		(1)	1				1											(1)					(1)
Ending balance (in shares) at Dec. 31, 2019			1,054	1						31					9					1
Ending 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	909	1,485	(26)	2,368	4,254	9,506	9,697	(198)	7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)		3,088				3,119		(31)
Net income after dividends on preferred stock		3,119							1,150			1,150							152			152		238						590		590
Net Income		3,103							1,165					1,575			1,575		152					207		238		238	(31)	590
Return of capital to parent company																			(74)		(74)
Capital contributions from parent company									658		658			1,399		1,399			86		86			2	2			2		233	233
Other comprehensive income (loss)		(75)					(75)		4				4	4				4	1				1	(42)			(42)	(42)		(29)			(29)
Stock issued (in shares)			4
Stock issued		74	$ 11		63
Stock-based compensation		44			44
Cash dividends on common stock		(2,685)				(2,685)			(957)			(957)		(1,542)			(1,542)		(74)			(74)		(201)		(201)		(201)		(533)		(533)
Contributions from noncontrolling interests		307						307																307					307
Distributions to noncontrolling interests		(271)						(271)																(271)					(271)
Sale of noncontrolling interests		65			(2)			67																65	(2)			(2)	67
Purchase of membership interests from noncontrolling interests		(60)			5			(65)																(60)	5			5	(65)
Other		(12)		$ (4)	(10)		1	1											(1)		(1)			2			1	1	1
Ending balance (in shares) at Dec. 31, 2020			1,058	1						31					9					1
Ending balance at Dec. 31, 2020		$ 32,234	$ 5,268	$ (46)	$ 11,834	$ 11,311	$ (395)	$ 4,262	$ 9,810	$ 1,222	$ 5,413	$ 3,194	$ (19)	$ 16,501	$ 398	$ 12,361	$ 3,789	$ (47)	$ 1,742	$ 38	$ 4,460	$ (2,754)	$ (2)	$ 6,631	$ 914	$ 1,522	$ (67)	$ 2,369	$ 4,262	$ 9,767	$ 9,930	$ (141)	$ (22)

[1] See Note 8 under "Equity Units" for additional information.