Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue	$ 690	$ 668	$ 1,361	$ 2,008
Cost of services, exclusive of depreciation and amortization	442	423	888	1,329
Depreciation and amortization	10	18	38	47
Gross Profit	238	227	435	632
Operating Expenses
Selling, general and administrative	135	128	222	364
Depreciation and intangible amortization	78	57	111	170
Total operating expenses	213	185	333	534
Operating Income	25	42	102	98
Other Expense	(2)	(4)	5	(28)
Loss from change in fair value of financial instruments	90
Loss from change in fair value of tax receivable agreement	27
Interest expense	28	61	123	172
Other expense (income), net		3	9	(1)
Total other expense, net	145	64	132	171
Loss Before Income Tax (Benefit) Expense	(120)	(22)	(30)	(73)
Income tax (benefit) expense		17	(5)	12
Net Loss	(120)	(39)	(25)	(85)
Net loss attributable to noncontrolling interests	(13)
Net Loss Attributable to Alight, Inc.	$ (107)	(39)	(25)	(85)
Earnings Per Share
Basic net loss per share	$ (0.24)
Diluted net loss per share	$ (0.24)
Other comprehensive (loss) income, net of tax:
Change in fair value of derivatives	$ (1)	4	23	(32)
Foreign currency translation adjustments	(2)	14	8	(7)
Total other comprehensive (loss) income, net of tax:	(3)	18	31	(39)
Comprehensive (Loss) Income Before Non-controlling Interests	(123)	(21)	6	(124)
Comprehensive loss attributable to noncontrolling interests	(13)
Comprehensive (Loss) Income Attributable to Alight, Inc.	$ (110)	$ (21)	$ 6	$ (124)