Earnings Per Share - Summary of Basic and Diluted (Net Loss) Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Numerator
Net Income (Loss) From Continuing Operations	$ (3,078)	$ (140)	$ (317)
Less: Net income (loss) attributable to noncontrolling interest	2	2	17
Net Income (loss) from continuing operations attributable to Alight, Inc.	(3,076)	(138)	(300)
Net Income (Loss) From Discontinued Operations, Net of Tax	(21)	(19)	(45)
Net Income (Loss) Attributable to Alight, Inc.	(3,097)	(157)	(345)
Loss impact of conversion of noncontrolling interest	0	(1)	0
Net income (loss) attributable to Alight, Inc. - diluted	$ (3,097)	$ (158)	$ (345)
Denominator
Weighted-average shares outstanding - basic (in shares)	527,567,685	539,861,208	489,461,259
Dilutive effect of the exchange of noncontrolling interest units (in shares)	0	510,237	0
Dilutive effect of RSUs (in shares)	0	0	0
Weighted-average shares outstanding - diluted (in shares)	527,567,685	540,371,445	489,461,259
Basic and Diluted (net loss) earnings per share
Continuing operations, basic (in dollars per share)	$ (5.83)	$ (0.25)	$ (0.61)
Continuing operations, diluted (in dollars per share)	(5.83)	(0.25)	(0.61)
Discontinued operations, basic (in dollars per share)	(0.04)	(0.04)	(0.09)
Discontinued operations, diluted (in dollars per share)	(0.04)	(0.04)	(0.09)
Net income (loss), basic (in dollars per share)	(5.87)	(0.29)	(0.70)
Net income (loss), diluted (in dollars per share)	$ (5.87)	$ (0.29)	$ (0.70)