Income Taxes - Schedule of (Loss) income before income tax expense (benefit) (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2023	Dec. 31, 2022
Income Tax Examination [Line Items]
U.S. (loss) income	$ (14)		$ (301)	$ (27)
Non-U.S. (loss) income	(9)		(65)	(14)
Income (Loss) Before Taxes	(23)		(366)	(41)
Alight Holdings
Income Tax Examination [Line Items]
U.S. (loss) income		$ (28)
Non-U.S. (loss) income		(2)
Income (Loss) Before Taxes	$ (23)	$ (30)	$ (366)	$ (41)