Earnings Per Share - Summary of Basic and Diluted (Net Loss) Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator
Net Income (Loss) From Continuing Operations	$ (121)	$ (84)
Less: Net loss attributable to noncontrolling interest	2	6
Net Income (loss) from continuing operations attributable to Alight, Inc.	(119)	(78)
Net Income (Loss) From Discontinued Operations, Net of Tax	5	10
Net Income (Loss) Attributable to Alight, Inc.	(114)	(68)
Loss impact of conversion of noncontrolling interest	(1)
Net (loss) income attributable to Alight, Inc. - diluted	$ (115)	$ (68)
Denominator
Weighted-average shares outstanding - basic	540,780,315	476,145,761
Dilutive effect of the exchange of noncontrolling interest units	1,189,156
Weighted-average shares outstanding - diluted	541,969,471	476,145,761
Basic (net loss) earnings per share
Continuing operations	$ (0.22)	$ (0.16)
Discontinued operations	0.01	0.02
Net Income (Loss)	(0.21)	(0.14)
Diluted (net loss) earnings per share
Continuing operations	(0.22)	(0.16)
Discontinued operations	0.01	0.02
Net Income (Loss)	$ (0.21)	$ (0.14)