Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Total Alight, Inc. Equity	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Noncontrolling Interest
Beginning balance at Dec. 31, 2023	$ 4,742	$ 4,462	$ 0	$ (52)	$ 4,946	$ (503)	$ 71	$ 280
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	(167)	(165)				(165)		(2)
Other comprehensive income (loss), net	(27)	(23)					(23)	(4)
Common stock issued under ESPP	6	6			6
Conversion of non-controlling interest	(72)	197			197			(269)
Share-based compensation expense	56	56			56
Shares withheld in lieu of taxes	(58)	(58)			(58)
Share repurchases	(155)	(155)		(155)
Other	1	2			2			(1)
Ending balance at Sep. 30, 2024	4,326	4,322	0	(207)	5,149	(668)	48	4
Beginning balance at Jun. 30, 2024	4,477	4,473	0	(132)	5,134	(594)	65	4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	(74)	(74)				(74)
Other comprehensive income (loss), net	(17)	(17)					(17)
Conversion of non-controlling interest	(1)	(1)			(1)
Share-based compensation expense	10	10			10
Share repurchases	(75)	(75)		(75)
Other	6	6			6
Ending balance at Sep. 30, 2024	4,326	4,322	0	(207)	5,149	(668)	48	4
Beginning balance at Dec. 31, 2024	4,313	4,309	0	(219)	5,141	(660)	47	4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	(2,167)	(2,165)				(2,165)		(2)
Other comprehensive income (loss), net	(17)	(17)					(17)
Common stock issued under ESPP	4	4			4
Share-based compensation expense	14	14			14
Shares withheld in lieu of taxes	(12)	(12)			(12)
Share repurchases	(65)	(65)		(65)
Dividends	(65)	(65)			(65)
Other	(1)	(1)			(1)
Ending balance at Sep. 30, 2025	2,004	2,002	0	(284)	5,081	(2,825)	30	2
Beginning balance at Jun. 30, 2025	3,121	3,118	0	(259)	5,101	(1,758)	34	3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	(1,068)	(1,067)				(1,067)		(1)
Other comprehensive income (loss), net	(4)	(4)					(4)
Share-based compensation expense	3	3			3
Shares withheld in lieu of taxes	(1)	(1)			(1)
Share repurchases	(25)	(25)		(25)
Dividends	(22)	(22)			(22)
Ending balance at Sep. 30, 2025	$ 2,004	$ 2,002	$ 0	$ (284)	$ 5,081	$ (2,825)	$ 30	$ 2