v3.26.1
Revenues - Additional Information (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Apr. 30, 2026
Dec. 31, 2021
Jun. 30, 2026
Dec. 31, 2025
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2023
Dec. 31, 2020
Disaggregation of Revenue [Line Items]                  
Contract with customer, liability     $ 56 $ 78   $ 56      
Total transaction price         $ 256   $ 256    
Contract with customer, liability, cumulative catch-up adjustment to revenue, change in measure of progress and change in estimate of transaction price         143        
Deferred revenue, non-refundable payment   $ 725              
Total revenues     41   160 58 188    
License and development services                  
Disaggregation of Revenue [Line Items]                  
Total transaction price         192   192    
Total revenues     16   152 28 172    
Access right and option continuation periods                  
Disaggregation of Revenue [Line Items]                  
Total revenues     21   5 24 11    
Gilead Collaboration | License and development services | Over time                  
Disaggregation of Revenue [Line Items]                  
Total revenues     8   152 15 172    
Taiho Collaboration Agreement                  
Disaggregation of Revenue [Line Items]                  
Milestone payments     30            
Taiho Collaboration | License and development services | Over time                  
Disaggregation of Revenue [Line Items]                  
Total revenues     4   0 6 0    
Taiho Collaboration | Other | Over time                  
Disaggregation of Revenue [Line Items]                  
Total revenues     6     8      
Casdatifan Collaboration | License and development services | Over time                  
Disaggregation of Revenue [Line Items]                  
Total revenues     2     2      
Gilead | R&D services                  
Disaggregation of Revenue [Line Items]                  
Total revenues     8   152 15 172    
Gilead | Access right and option continuation periods                  
Disaggregation of Revenue [Line Items]                  
Total revenues $ 18                
Current and future programs exclusive access period                 10 years
Contingent milestone payments receivable                 $ 300
Option continuation payment receivable upon sixth anniversary of agreement                 $ 100
Gilead | Rights to certain studies                  
Disaggregation of Revenue [Line Items]                  
Contract with customer, liability     14     14      
Gilead | R&D Activities for Inflammation Programs                  
Disaggregation of Revenue [Line Items]                  
Total revenues     $ 4   $ 3 $ 6 $ 5    
Gilead | Revenue Benchmark | Customer Concentration Risk                  
Disaggregation of Revenue [Line Items]                  
Percentage of revenues     80.00%   100.00% 83.00% 100.00%    
STAR-221 Development Activities | Taiho Collaboration Agreement                  
Disaggregation of Revenue [Line Items]                  
Contract with customer, liability               $ 35  
Milestone payments               $ 28  
Taiho Pharmaceutical Co., Ltd                  
Disaggregation of Revenue [Line Items]                  
Total transaction price       15          
Taiho Pharmaceutical Co., Ltd | Taiho Agreement                  
Disaggregation of Revenue [Line Items]                  
Contract with customer, liability       7          
Payment for option exercise       $ 15