Revenues - Additional Information (Details) $ / shares in Units, $ in Millions	1 Months Ended			3 Months Ended	12 Months Ended
	Jul. 31, 2024 USD ($)	Jan. 31, 2024 USD ($)	May 31, 2023 program	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) $ / shares	Dec. 31, 2023 USD ($) program	Dec. 31, 2022 USD ($)	Mar. 31, 2024 USD ($)	Jan. 29, 2024 USD ($)	Jan. 28, 2024 USD ($)
Disaggregation of Revenue [Line Items]
Contract with customer, liability					$ 319	$ 398			$ 522
Contract with customer, liability, cumulative catch-up adjustment to revenue, change in measure of progress and change in estimate of transaction price		$ 107
Contract with customer, liability, cumulative catch-up adjustment to revenue, earnings per share, basic (in dollars per share) | $ / shares					$ 1.19
Option continuation payment received in the third quarter of 2024									100
Premium from Third Stock Purchase Agreement Amendment									87
Deferred revenue as of January 2024		335							335
Total revenues					$ 51	37	$ 38
Licensing revenue recognized					243	$ 108	112
Number of programs, eligible to receive regulatory and commercial milestone payments | program			4			4
Capitalized contract cost, amortization					3	$ 1	4
Cost sharing receivable					3
Amended Gilead Collaboration Agreement
Disaggregation of Revenue [Line Items]
Number of programs, eligible to receive regulatory and commercial milestone payments | program						2,000,000
Amended Gilead Collaboration Agreement | Related Party
Disaggregation of Revenue [Line Items]
Number of research programs | program						2
Domvanalimab - R&D services
Disaggregation of Revenue [Line Items]
Licensing revenue recognized					25
R&D and Commercialization Activities for Zimberelimab
Disaggregation of Revenue [Line Items]
Total revenues						$ 1	9
Access Rights and Option Continuation Periods
Disaggregation of Revenue [Line Items]
Contract with customer, liability					52	54
Total revenues					28	33	33
Third Gilead Collaboration Agreement Amendment, Third Stock Purchase Agreement Amendment and the Second Investor Rights Agreement Amendment
Disaggregation of Revenue [Line Items]
Capitalized contract cost, gross								$ 8
Third Stock Purchase Agreement Amendment
Disaggregation of Revenue [Line Items]
Capitalized contract cost, gross					5
Initial Gilead Collaboration Agreement and Subsequent Amendments
Disaggregation of Revenue [Line Items]
Capitalized contract cost, gross					3
Gilead
Disaggregation of Revenue [Line Items]
Contract with customer, liability									522
Gilead | Etrumadenant - License and R&D services
Disaggregation of Revenue [Line Items]
Contract with customer, liability					166	133			210	$ 129
Contract with customer liability revenue recognized excluding opening balance					250
Contract with customer, liability, cumulative catch-up adjustment to revenue, change in measure of progress		14
Total revenues					47	52	34
Gilead | Quemliclustat - License and R&D services
Disaggregation of Revenue [Line Items]
Contract with customer, liability					23	132			168	$ 130
Contract with customer liability revenue recognized excluding opening balance					200
Contract with customer, liability, cumulative catch-up adjustment to revenue, change in measure of progress		88
Total revenues					147	17	26
Gilead | Domvanalimab - R&D services
Disaggregation of Revenue [Line Items]
Contract with customer, liability					21	25			33
Total revenues					$ 13	5	$ 5
Contract with customer, liability, cumulative catch-up adjustment to revenue, change in estimate of transaction price		5
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		200			$ 300
Option continuation payment receivable upon sixth anniversary of agreement		$ 100			100
Deferred revenue related to access rights and option					51
Gilead | Rights to certain studies
Disaggregation of Revenue [Line Items]
Contract with customer, liability					34				$ 34
Gilead | Research and Development Activities for Inflammation Programs
Disaggregation of Revenue [Line Items]
Contract with customer, liability					23	31
Total revenues					8	$ 4
Gilead | Third Stock Purchase Agreement Amendment
Disaggregation of Revenue [Line Items]
Capitalized contract cost, gross					$ 5
Gilead | Revenue Benchmark | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percentage of revenues					94.00%	96.00%	96.00%
STAR-221 Development Activities | Taiho Collaboration Agreement
Disaggregation of Revenue [Line Items]
Contract with customer, liability						$ 35
Payment for option exercise						28
Taiho Pharmaceutical Co., Ltd | Taiho Agreement
Disaggregation of Revenue [Line Items]
Total revenues					$ 15	$ 5	$ 5
Payment for option exercise	$ 15			$ 15	$ 15