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Revenues - Additional Information (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Apr. 30, 2026 | Dec. 31, 2021 | Mar. 31, 2026 | Dec. 31, 2025 | Jun. 30, 2025 | Mar. 31, 2025 | Dec. 31, 2020 | Dec. 31, 2023
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Contract with customer, liability |  |  | $ 79 | $ 78 |  |  |  |
Total transaction price |  |  |  |  | $ 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 |  |  | 17 |  |  | $ 28 |  |
License and development services |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total transaction price |  |  |  |  | $ 192 |  |  |
Total revenues |  |  | 12 |  |  | 20 |  |
Access right and option continuation periods |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total revenues |  |  | 3 |  |  | 6 |  |
Gilead Collaboration | Other | Over time |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total revenues |  |  | 2 |  |  | 0 |  |
Gilead Collaboration | License and development services | Over time |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total revenues |  |  | 8 |  |  | 20 |  |
Taiho Collaboration | License and development services | Over time |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total revenues |  |  | 2 |  |  |  |  |
Gilead | R&D services |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total revenues |  |  | 8 |  |  | 20 |  |
Gilead | Access right and option continuation periods |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
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 | Access right and option continuation periods | Subsequent event |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total revenues | $ 18 |  |  |  |  |  |  |
Gilead | Rights to certain studies |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Contract with customer, liability |  |  | 14 |  |  |  |  |
Gilead | R&D Activities for Inflammation Programs |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Total revenues |  |  | $ 2 |  |  | $ 2 |  |
Gilead | Revenue Benchmark | Customer Concentration Risk |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Percentage of revenues |  |  | 88.00% |  |  | 100.00% |  |
STAR-221 Development Activities | Taiho Collaboration Agreement |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |
Contract with customer, liability |  |  |  |  |  |  |  | $ 35
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 |  |  |  |

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