Revenues - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2025	Dec. 31, 2021	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2020	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Contract with customer, liability			$ 105		$ 105			$ 319
Deferred revenue, transaction price	$ 256		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
Contract with customer, liability, cumulative catch-up adjustment to revenue, earnings per share, diluted (in dollars per share)					$ 1.38
Contract with customer, liability, cumulative catch-up adjustment to revenue, earnings per share, basic (in dollars per share)					$ 1.38
Deferred revenue, non-refundable payment		$ 725
Total revenues			26	$ 48	$ 214	$ 232
Access rights and option continuation periods
Disaggregation of Revenue [Line Items]
Total revenues			3	5	14	22
Gilead | R&D services
Disaggregation of Revenue [Line Items]
Total revenues			20	23	192	179
Gilead | Access rights 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 | Rights to certain studies
Disaggregation of Revenue [Line Items]
Contract with customer, liability			17		17
Gilead | R&D Activities for Inflammation Programs
Disaggregation of Revenue [Line Items]
Total revenues			$ 3	$ 2	$ 8	$ 6
Gilead | Revenue Benchmark | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percentage of revenues			100.00%	63.00%	100.00%	89.00%
STAR-221 Development Activities | Taiho Collaboration Agreement
Disaggregation of Revenue [Line Items]
Contract with customer, liability									$ 35