Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - GAS - USD ($) $ in Millions	Total	Paid-In Capital	Retained Earnings	SOUTHERN Co GAS	SOUTHERN Co GAS Paid-In Capital	SOUTHERN Co GAS Retained Earnings	SOUTHERN Co GAS Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2024				$ 10,996	$ 10,863	$ 85	$ 48
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 1,334			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, 2025				11,127	10,854	222	51
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,356			447		447
Capital contributions from parent company				1	1
Other comprehensive income				(2)			(2)
Cash dividends on common stock	(830)		$ (830)	(141)		(141)
Other	$ (3)	$ (1)		1		1
Ending balance at Mar. 31, 2026				$ 11,433	$ 10,855	$ 529	$ 49