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, 2022	$ 34,532	$ 13,673	$ 11,538	$ (167)	$ 10,397	$ 10,445	$ (79)	$ 31
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					309		309
Capital contributions from parent company					203	203
Other comprehensive income (loss)	(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]
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]
Net income					85		85
Capital contributions from parent company					40	40
Other comprehensive income (loss)	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]
Net income	1,432				82		82
Capital contributions from parent company					149	149
Other comprehensive income (loss)	38			38	10			10
Cash dividends on common stock	(765)		(765)		(146)		(146)
Other	(1)	(2)	2	0
Ending balance at Sep. 30, 2023	35,304	13,751	12,391	(130)	10,833	10,838	(43)	38
Beginning balance at Dec. 31, 2023	35,225	13,775	12,482	(177)	10,803	10,836	(49)	16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					409		409
Capital contributions from parent company					2	2
Other comprehensive income (loss)	37			37	12			12
Cash dividends on common stock	(766)		(766)		(151)		(151)
Other	7	10	(1)		(1)		(1)
Ending balance at Mar. 31, 2024	35,614	13,846	12,844	(140)	11,074	10,838	208	28
Beginning balance at Dec. 31, 2023	35,225	13,775	12,482	(177)	10,803	10,836	(49)	16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	3,794				555
Ending balance at Sep. 30, 2024	36,905	14,048	14,005	(139)	10,928	10,845	52	31
Beginning balance at Mar. 31, 2024	35,614	13,846	12,844	(140)	11,074	10,838	208	28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					108		108
Capital contributions from parent company					6	6
Other comprehensive income (loss)	10			10	7			7
Cash dividends on common stock	(788)		(788)		(151)		(151)
Other	1	3	0	0
Ending balance at Jun. 30, 2024	36,111	13,947	13,259	(130)	11,044	10,844	165	35
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,535				38		38
Capital contributions from parent company					1	1
Other comprehensive income (loss)	(9)			(9)	(4)			(4)
Cash dividends on common stock	(789)		(789)		(152)		(152)
Other	4	(2)	0	0	1		1	0
Ending balance at Sep. 30, 2024	$ 36,905	$ 14,048	$ 14,005	$ (139)	$ 10,928	$ 10,845	$ 52	$ 31