Cover - shares	9 Months Ended
	Sep. 30, 2025	Oct. 30, 2025
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2025
Document Transition Report	false
Entity File Number	001-39299
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	86-1849232
Entity Address, Address Line One	320 South Canal Street,
Entity Address, Address Line Two	50th Floor, Suite 5000
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	(224)
Local Phone Number	737-7000
Title of 12(b) Security	Class A Common Stock, par value $0.0001 per share
Trading Symbol	ALIT
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Amendment Flag	false
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001809104
Current Fiscal Year End Date	--12-31
Entity Registrant Name	Alight, Inc. / Delaware
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		522,778,829
Class B-1 Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		4,955,297
Class B-2 Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		4,955,297
Class V Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		510,115