Income Taxes - Schedule of Reconciliation of The Effective Tax Rate (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2023	Dec. 31, 2022
Income Tax Contingency [Line Items]
(Loss) income before income tax expense (benefit)	$ (23)		$ (366)	$ (41)
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Provision for income taxes at the statutory rate	(5)		(77)	(9)
State income taxes, net of federal benefit	3		(1)	3
Jurisdictional rate differences	(11)		10	8
Changes in valuation allowances	23		10	39
Benefit of income not allocated to the Company	1		2	6
Income in separate U.S. tax consolidations	16		1	15
Non-deductible expenses	8		63	4
Tax credits	(4)		(14)	(7)
Change in uncertain tax positions	(5)			(28)
Other	(1)		2
Total income tax expense (benefit)	$ 25		$ (4)	$ 31
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Provision for income taxes at the statutory rate	21.00%		21.00%	21.00%
State income taxes, net of federal benefit	(12.00%)			(7.00%)
Jurisdictional rate differences	49.00%		(3.00%)	(20.00%)
Changes in valuation allowances	(100.00%)		(3.00%)	(95.00%)
Benefit of income not allocated to the Company	(4.00%)		(1.00%)	(14.00%)
Income in separate U.S. tax consolidations	(68.00%)			(37.00%)
Non-deductible expenses	(35.00%)		(17.00%)	(9.00%)
Tax credits	19.00%		4.00%	17.00%
Change in uncertain tax positions	24.00%			68.00%
Other	(3.00%)
Income tax expense (benefit)	(109.00%)	16.00%	1.00%	(76.00%)
Alight Holdings
Income Tax Contingency [Line Items]
(Loss) income before income tax expense (benefit)	$ (23)	$ (30)	$ (366)	$ (41)
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Jurisdictional rate differences		1
Changes in valuation allowances		(2)
Non-deductible expenses		(2)
Other		(2)
Total income tax expense (benefit)		$ (5)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Jurisdictional rate differences		(3.00%)
Changes in valuation allowances		6.00%
Non-deductible expenses		6.00%
Other		7.00%
Income tax expense (benefit)		16.00%

Effective income tax rate reconciliation benefit of income not allocated to company.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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