Earnings Per Share - Summary of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2022
Numerator
Net income attributable to Alight, Inc. - basic	$ 51	$ 40
Income (loss) impact of conversion of noncontrolling interest	1	(1)
Net income attributable to Alight, Inc. - diluted	$ 52	$ 39
Denominator
Weighted-average shares outstanding - basic	457,851,348	457,347,581
Dilutive effect of the exchange of noncontrolling interest units	75,886,716	75,886,716
Dilutive effect of RSUs		836,356
Weighted-average shares outstanding - diluted	533,738,064	534,070,653
Basic earnings per share	$ 0.11	$ 0.09
Diluted earnings per share	$ 0.10	$ 0.07