Consolidated Statements of Common Stockholders' Equity - GAS - USD ($) $ in Millions	Total	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Southern Company Gas	Southern Company Gas Paid-In Capital	Southern Company Gas Retained Earnings	Southern Company Gas Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2018	$ 29,039	$ 11,094	$ 8,706	$ (203)	$ 8,570	$ 8,856	$ (312)	$ 26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	4,744				585		585
Capital contributions from parent company					841	841
Other comprehensive income (loss)	(118)			(118)	(19)			(19)
Cash dividends on common stock	(2,570)		(2,570)		(471)		(471)
Ending balance at Dec. 31, 2019	31,759	11,734	10,877	(321)	9,506	9,697	(198)	7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	3,103				590		590
Capital contributions from parent company					233	233
Other comprehensive income (loss)	(75)			(75)	(29)			(29)
Cash dividends on common stock	(2,685)		(2,685)		(533)		(533)
Ending 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 (Loss)	2,309				539		539
Capital contributions from parent company					94	94
Other comprehensive income (loss)	158			158	46			46
Cash dividends on common stock	(2,777)		(2,777)		(530)		(530)
Ending balance at Dec. 31, 2021	$ 32,276	$ 11,950	$ 10,929	$ (237)	$ 9,916	$ 10,024	$ (132)	$ 24