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, 2021	$ 32,276	$ 11,950	$ 10,929	$ (237)	$ 9,916	$ 10,024	$ (132)	$ 24
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated Net Income					319		319
Capital contributions from parent company					50	50
Other comprehensive income	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]
Consolidated 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]
Consolidated Net Income					115		115
Capital contributions from parent company					312	312
Other comprehensive income	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]
Consolidated Net Income	1,487				83		83
Capital contributions from parent company					11	11
Other comprehensive income	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
Beginning balance at Dec. 31, 2022	34,532	13,673	11,538	(167)	10,397	10,445	(79)	31
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated Net Income					309		309
Capital contributions from parent company					203	203
Other comprehensive income	(44)			(44)	(10)			(10)
Cash dividends on common stock	(742)		(742)		(146)		(146)
Other	0	2			0	1	(1)
Ending balance at Mar. 31, 2023	34,562	13,715	11,658	(211)	10,753	10,649	83	21
Beginning balance at Dec. 31, 2022	34,532	13,673	11,538	(167)	10,397	10,445	(79)	31
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated Net Income	3,053				475
Ending balance at Sep. 30, 2023	35,304	13,751	12,391	(130)	10,833	10,838	(43)	38
Beginning balance at Mar. 31, 2023	34,562	13,715	11,658	(211)	10,753	10,649	83	21
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated Net Income					85		85
Capital contributions from parent company					40	40
Other comprehensive income	43			43	7			7
Cash dividends on common stock	(764)		(764)		(147)		(147)
Other	0	2
Ending balance at Jun. 30, 2023	34,648	13,742	11,732	(168)	10,738	10,689	21	28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated Net Income	1,432				82		82
Capital contributions from parent company					149	149
Other comprehensive income	38			38	10			10
Cash dividends on common stock	(765)		(765)		(146)		(146)
Other	(1)	(2)	2
Ending balance at Sep. 30, 2023	$ 35,304	$ 13,751	$ 12,391	$ (130)	$ 10,833	$ 10,838	$ (43)	$ 38