| Document and Entity Information | Sep. 07, 2021 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | Alight, Inc. / Delaware |
| Amendment Flag | false |
| Entity Central Index Key | 0001809104 |
| Document Type | 8-K |
| Document Period End Date | Sep. 7, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39299 |
| Entity Tax Identification Number | 86-1849232 |
| Entity Address, Address Line One | 4 Overlook Point |
| Entity Address, City or Town | Lincolnshire |
| Entity Address, Country | IL |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60069 |
| City Area Code | (224) |
| Local Phone Number | 737-7000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Class A Common Stock Par Value 0.0001 Per Share 2 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Class A Common Stock, par value $0.0001 per share |
| Trading Symbol | ALIT |
| Security Exchange Name | NYSE |
| Warrants To Purchase One Share Of Class A Common Stock 1 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Warrants to purchase one share of Class A Common Stock |
| Trading Symbol | ALIT.WS |
| Security Exchange Name | NYSE |
