Stockholders' Equity - Additional Information (Details) $ / shares in Units, $ in Millions			3 Months Ended				9 Months Ended
	Nov. 05, 2025 $ / shares	Jul. 02, 2021 shares	Sep. 30, 2025 USD ($) Vote series $ / shares shares	Jun. 30, 2025 $ / shares shares	Mar. 31, 2025 $ / shares	Sep. 30, 2024 USD ($) shares	Sep. 30, 2025 USD ($) Vote series $ / shares shares	Sep. 30, 2024 USD ($) shares	Feb. 13, 2025 USD ($)	Dec. 31, 2024 $ / shares shares	Jun. 30, 2024 shares	Dec. 31, 2023 shares
Class Of Stock [Line Items]
Preferred stock, shares authorized (in shares)			1,000,000				1,000,000			1,000,000.0
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.0001				$ 0.0001			$ 0.0001
Preferred stock, shares outstanding (in shares)			0				0			0
Preferred stock, shares issued (in shares)			0				0			0
Conversion ratio			1				1
Remaining authorized amount for future share repurchase program | $			$ 216				$ 216
Share repurchases | $			$ 25			$ 75	$ 65	$ 155
Treasury
Class Of Stock [Line Items]
Number of shares repurchased (in shares)			6,580,136			10,563,306	13,881,417	20,697,906
Share repurchases | $			$ 25			$ 75	$ 65	$ 155
Class A Common Stock
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			522,640,188				522,640,188			531,700,000
Common shares, votes per share | Vote			1				1
Common stock, shares issued (in shares)			565,200,000				565,200,000			560,500,000
Common stock, shares authorized (in shares)			1,000,000,000				1,000,000,000			1,000,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.0001				$ 0.0001			$ 0.0001
Common stock repurchase, additional authorized amount | $									$ 200
Common stock repurchase, authorized amount | $									$ 281
Number of shares repurchased (in shares)			6,580,136				13,881,417
Common stock dividends declared (in usd per share) | $ / shares			$ 0.04	$ 0.04	$ 0.04
Class A Common Stock | Subsequent Events
Class Of Stock [Line Items]
Common stock dividends declared (in usd per share) | $ / shares	$ 0.04
Class B Common Stock
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			9,900,000				9,900,000			10,000,000.0
Issuance of common units (in shares)		14,999,998
Number of common stock instruments | series			2				2
Common stock, shares issued (in shares)			9,900,000				9,900,000			10,000,000.0
Common stock, shares authorized (in shares)			20,000,000.0				20,000,000.0			20,000,000.0
Common stock, par value (in dollars per share) | $ / shares			$ 0.0001				$ 0.0001			$ 0.0001
Class B-1 Common Stock
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			4,955,297				4,955,297
Common stock, shares issued (in shares)			4,955,297				4,955,297
Common stock shares conversion ratio							1
Common stock shares convertible stock price trigger (in dollars per share) | $ / shares							$ 12.50
Common stock shares convertible threshold trading days							20 days
Common stock shares convertible threshold consecutive trading days							30 days
Common stock shares convertible stock valuation price on diluted basis (in dollars per share) | $ / shares							$ 12.50
Class B-1 Common Units | Alight Holdings
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			2,544,702				2,544,702
Common stock, shares issued (in shares)			2,544,702				2,544,702
Common stock shares conversion ratio							1
Common stock shares convertible stock price trigger (in dollars per share) | $ / shares							$ 12.50
Common stock shares convertible threshold trading days							20 days
Common stock shares convertible threshold consecutive trading days							30 days
Common stock shares convertible stock valuation price on diluted basis (in dollars per share) | $ / shares							$ 12.50
Class B-2 Common Stock
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			4,955,297				4,955,297
Common stock, shares issued (in shares)			4,955,297				4,955,297
Common stock shares conversion ratio							1
Common stock shares convertible stock price trigger (in dollars per share) | $ / shares							$ 15.00
Common stock shares convertible threshold trading days							20 days
Common stock shares convertible threshold consecutive trading days							30 days
Common stock shares convertible stock valuation price on diluted basis (in dollars per share) | $ / shares							$ 15.00
Class B-2 Common Units | Alight Holdings
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			2,544,702				2,544,702
Common stock, shares issued (in shares)			2,544,702				2,544,702
Common stock shares conversion ratio							1
Common stock shares convertible stock price trigger (in dollars per share) | $ / shares							$ 15.00
Common stock shares convertible threshold trading days							20 days
Common stock shares convertible threshold consecutive trading days							30 days
Common stock shares convertible stock valuation price on diluted basis (in dollars per share) | $ / shares							$ 15.00
Class B-3 Common Stock
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			0				0
Common stock, shares issued (in shares)			0				0
Common stock, shares authorized (in shares)			10,000,000				10,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.0001				$ 0.0001
Class V Common Stock
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			510,115	510,115		560,433	510,115	560,433		510,237	554,568	28,962,218
Common shares, votes per share | Vote			1				1
Common stock, shares issued (in shares)			500,000				500,000			500,000
Common stock shares conversion ratio							1
Common stock, shares authorized (in shares)			175,000,000.0				175,000,000.0			175,000,000.0
Common stock, par value (in dollars per share) | $ / shares			$ 0.0001				$ 0.0001			$ 0.0001
Shares issued (in shares)							510,115
Class Z Common Stock
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			0	0		0	0	0		0	578,099	3,420,215
Common stock, shares issued (in shares)		8,671,507	0.0				0.0			0.0
Common stock, shares authorized (in shares)			12,900,000				12,900,000			12,900,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.0001				$ 0.0001			$ 0.0001
Class Z Common Units
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			0				0
Class A Units
Class Of Stock [Line Items]
Common stock, shares outstanding (in shares)			523,150,303				523,150,303
Held by non controlling interest (in shares)							510,115