Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - GAS - USD ($) $ in Millions	Total	Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	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 at Dec. 31, 2020	$ 32,234	$ 11,834	$ 11,311	$ (395)	$ 9,767	$ 9,930	$ (141)	$ (22)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					398		398
Capital contributions from parent company					57	57
Other comprehensive income (loss)	28			28	4			4
Cash dividends on common stock	(678)		(678)		(132)		(132)
Other	1	2
Ending balance at Mar. 31, 2021	33,068	11,854	11,768	(367)	10,094	9,987	125	(18)
Beginning balance at Dec. 31, 2020	32,234	11,834	11,311	(395)	9,767	9,930	(141)	(22)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,592				389
Ending balance at Sep. 30, 2021	33,219	11,932	11,844	(319)	9,876	10,014	(149)	11
Beginning balance at Mar. 31, 2021	33,068	11,854	11,768	(367)	10,094	9,987	125	(18)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					(65)		(65)
Capital contributions from parent company					25	25
Other comprehensive income (loss)	12			12	8			8
Cash dividends on common stock	(699)		(699)		(133)		(133)
Other	0	1	1
Ending balance at Jun. 30, 2021	32,746	11,886	11,442	(355)	9,929	10,012	(73)	(10)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,110				56		56
Capital contributions from parent company					2	2
Other comprehensive income (loss)	36			36	21			21
Cash dividends on common stock	(700)		(700)		(132)		(132)
Other	(7)	(10)	1
Ending balance at Sep. 30, 2021	33,219	11,932	11,844	(319)	9,876	10,014	(149)	11
Beginning balance at Dec. 31, 2021	32,276	11,950	10,929	(237)	9,916	10,024	(132)	24
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					319		319
Capital contributions from parent company					50	50
Other comprehensive income (loss)	42			42	20			20
Cash dividends on common stock	(702)		(702)		(130)		(130)
Other	7	7	2
Ending balance at Mar. 31, 2022	32,629	11,994	11,261	(195)	10,175	10,074	57	44
Beginning balance at Dec. 31, 2021	32,276	11,950	10,929	(237)	9,916	10,024	(132)	24
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	3,566				516
Ending balance at Sep. 30, 2022	35,476	13,657	12,374	(157)	10,438	10,397	(5)	46
Beginning balance at Mar. 31, 2022	32,629	11,994	11,261	(195)	10,175	10,074	57	44
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					115		115
Capital contributions from parent company					312	312
Other comprehensive income (loss)	11			11	(12)			(12)
Cash dividends on common stock	(723)		(723)		(130)		(130)
Other	2	4
Ending balance at Jun. 30, 2022	33,013	12,033	11,645	(184)	10,460	10,386	42	32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,487				83		83
Capital contributions from parent company					11	11
Other comprehensive income (loss)	28			28	14			14
Cash dividends on common stock	(741)		(741)		(130)		(130)
Other	(8)	(4)	(2)	(1)
Ending balance at Sep. 30, 2022	$ 35,476	$ 13,657	$ 12,374	$ (157)	$ 10,438	$ 10,397	$ (5)	$ 46