Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - GAS - USD ($) $ in Millions	Total	Paid-In Capital	Retained Earnings (Accumulated Deficit)	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, 2023				$ 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				12			12
Cash dividends on common stock	$ (766)		$ (766)	(151)		(151)
Other	7	$ 10	(1)	(1)		(1)
Ending balance at Mar. 31, 2024				11,074	10,838	208	28
Beginning balance at Dec. 31, 2023				10,803	10,836	(49)	16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,332			517
Other comprehensive income				19
Ending balance at Jun. 30, 2024				11,044	10,844	165	35
Beginning balance at Mar. 31, 2024				11,074	10,838	208	28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,203			108		108
Capital contributions from parent company				6	6
Other comprehensive income				7			7
Cash dividends on common stock	(788)		(788)	(151)		(151)
Other	1	3
Ending balance at Jun. 30, 2024				11,044	10,844	165	35
Beginning balance at Dec. 31, 2024				10,996	10,863	85	48
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				418		418
Return of capital to parent company				(56)	(56)
Capital contributions from parent company				3	3
Other comprehensive income				12			12
Cash dividends on common stock	(791)		(791)	(149)		(149)
Other	(5)	(1)	(2)	1		1
Ending balance at Mar. 31, 2025				11,225	10,810	355	60
Beginning balance at Dec. 31, 2024				10,996	10,863	85	48
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,214			524
Other comprehensive income				5
Ending balance at Jun. 30, 2025				11,198	10,833	312	53
Beginning balance at Mar. 31, 2025				11,225	10,810	355	60
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	880			106		106
Capital contributions from parent company				23	23
Other comprehensive income				(7)			(7)
Cash dividends on common stock	(815)		(815)	(148)		(148)
Other	$ 6	$ 6	$ 1	(1)		(1)
Ending balance at Jun. 30, 2025				$ 11,198	$ 10,833	$ 312	$ 53