Segment Reporting - Schedule of Current Reportable and Recast of Segments by Segment Profit (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2022	Sep. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Selling, general and administrative	$ 185		$ 140
Depreciation and intangible amortization	85		85
Operating Income (Loss)	(13)		(2)
(Gain) Loss from change in fair value of financial instruments	25		(13)
(Gain) loss from change in fair value of tax receivable agreement	8		(5)
Interest expense	33		29
Other (income) expense, net	3		(1)
Income (Loss) Before Taxes	(82)		(12)
Alight Holdings
Segment Reporting Information [Line Items]
Segment Profit	257	$ 212	223	$ 219	$ 442	$ 654	$ 996
Selling, general and administrative	185	178	140	157	297	475	671
Depreciation and intangible amortization	85	84	85	85	170	254	339
Operating Income (Loss)	(13)	(50)	(2)	(23)	(25)	(75)	(14)
(Gain) Loss from change in fair value of financial instruments	25	10	(13)	(50)	(63)	(53)	(38)
(Gain) loss from change in fair value of tax receivable agreement	8	(20)	(5)	(38)	(43)	(63)	(41)
Interest expense	33	31	29	29	58	89	122
Other (income) expense, net	3	(6)	(1)	(7)	(8)	(14)	(16)
Income (Loss) Before Taxes	(82)	(65)	(12)	43	31	(34)	(41)
Employer Solutions
Segment Reporting Information [Line Items]
Segment Profit	238	189	204	200	404	593	911
Professional Services
Segment Reporting Information [Line Items]
Segment Profit	$ 19	$ 23	$ 19	20	39	62	86
Other
Segment Reporting Information [Line Items]
Segment Profit				$ (1)	$ (1)	$ (1)	$ (1)