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	1,107				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)
Ending balance at Mar. 31, 2021	33,068	11,854	11,768	(367)	10,094	9,987	125	(18)
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)
Ending balance at Mar. 31, 2022	$ 32,629	$ 11,994	$ 11,261	$ (195)	$ 10,175	$ 10,074	$ 57	$ 44