Restructuring and Integration - Summary of Restructuring Costs (Details) - USD ($)
$ in Millions
 6 Months Ended
Dec. 31, 2021
Jun. 30, 2021
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs $ 5  
Inception to Date 105  
Estimated Remaining Costs 35  
Estimated Total Cost [1] 140  
Alight Holdings    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs   $ 9
Employer Solutions    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs 4  
Inception to Date 91  
Estimated Remaining Costs 30  
Estimated Total Cost [1] 121  
Employer Solutions | Alight Holdings    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs   8
Employer Solutions | Severance and Related Benefits    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs 1  
Inception to Date 46  
Estimated Remaining Costs 13  
Estimated Total Cost [1] 59  
Employer Solutions | Severance and Related Benefits | Alight Holdings    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs   6
Employer Solutions | Other Restructuring Costs    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs [2] 3  
Inception to Date [2] 45  
Estimated Remaining Costs [2] 17  
Estimated Total Cost [1],[2] 62  
Employer Solutions | Other Restructuring Costs | Alight Holdings    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs [2]   2
Professional Services    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs 1  
Inception to Date 14  
Estimated Remaining Costs 5  
Estimated Total Cost [1] 19  
Professional Services | Alight Holdings    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs   1
Professional Services | Severance and Related Benefits    
Restructuring Cost And Reserve [Line Items]    
Inception to Date 8  
Estimated Remaining Costs 2  
Estimated Total Cost [1] 10  
Professional Services | Severance and Related Benefits | Alight Holdings    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs   $ 1
Professional Services | Other Restructuring Costs    
Restructuring Cost And Reserve [Line Items]    
Restructuring Costs [2] 1  
Inception to Date [2] 6  
Estimated Remaining Costs [2] 3  
Estimated Total Cost [1],[2] $ 9  
[1] Actual costs, when incurred, may vary due to changes in the assumptions built into the Plan. Significant assumptions that may change when plans are finalized and implemented include, but are not limited to, changes in severance calculations, changes in the assumptions underlying sublease loss calculations due to changing market conditions, and changes in the overall analysis that might cause the Company to add or cancel component initiatives.
[2] Other costs associated with the Plan primarily include consulting and legal fees and lease consolidation.