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	799				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, 2023	35,225	13,775	12,482	(177)	10,803	10,836	(49)	16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,071				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