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]
Net income	991				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, 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