Revenue - Additional Information (Details) - USD ($) $ in Millions			1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 01, 2024	Jul. 13, 2020	Jun. 30, 2023	Jan. 31, 2022	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue recognized from amounts in deferred revenue at the beginning of the period						$ 108	$ 112	$ 202
Revenue from contract with customer, excluding assessed tax						117	112	383
Receivable from collaboration partners, current					$ 38	38	39
Gilead Collaboration Agreement
Disaggregation of Revenue [Line Items]
Contract with customer, liability					398	398	452
Amended Gilead Collaboration Agreement
Disaggregation of Revenue [Line Items]
Upfront cash payment						725
Deferred revenue					165	165
Option continuation payment due upon second anniversary of agreement					100	100
Initial transaction price						890
Option payments received				$ 725
Domvanalimab R&D services
Disaggregation of Revenue [Line Items]
Deferred revenue					25	25
Revenue from contract with customer, excluding assessed tax						5	5	0
Quemliclustat, License and R&D services
Disaggregation of Revenue [Line Items]
Contract with customer, liability					0	0
Option payment upon achievement of certain development milestones						200
R&D and Commercialization Activities for Zimberelimab
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax						1	9	1
Deferred revenue related to development and commercialization services					10	10
Access Rights and Option Continuation Periods
Disaggregation of Revenue [Line Items]
Deferred revenue					54	54
Revenue from contract with customer, excluding assessed tax						33	33	31
Gilead | Gilead Collaboration Agreement
Disaggregation of Revenue [Line Items]
Contract with customer, liability					127	127
Upfront cash payment			$ 35
Deferred revenue					133	133
Option payment upon achievement of certain development milestones						275
Deferred revenue related to domvanalimab option					37	37
Revenue recognized from amounts in deferred revenue at the beginning of the period								329
Revenue from contract with customer, excluding assessed tax						$ 52	34	0
Option payment upon achievement of certain development milestones		$ 250
Current and future programs exclusive access period						10 years
Contingent milestone payments receivable					300	$ 300
Option continuation payment receivable upon sixth anniversary of agreement					100	100
Deferred revenue related to access rights and option					92	$ 92
Performance obligation period						4 years
Contractual obligation remaining amount not obligated to pay						$ 300
Gilead | Quemliclustat, License and R&D services
Disaggregation of Revenue [Line Items]
Deferred revenue					132	132
Revenue from contract with customer, excluding assessed tax						17	$ 26	$ 0
Gilead | Research and Development Activities for Inflammation Programs
Disaggregation of Revenue [Line Items]
Contract with customer, liability					31	31
Revenue from contract with customer, excluding assessed tax						$ 4
Gilead | Revenue Benchmark | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percentage of revenues						96.00%	96.00%	94.00%
STAR-221 Development Activities | Taiho Collaboration Agreement
Disaggregation of Revenue [Line Items]
Contract with customer, liability					23	$ 23
Revenue from contract with customer, excluding assessed tax					14	5
Licensing revenue recognized						28
Receivable from collaboration partners, current					$ 14	14
Taiho Pharmaceutical Co., Ltd | Taiho Agreement
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax						5	$ 5	$ 22
Payment for option exercise						$ 28
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Subsequent Event
Disaggregation of Revenue [Line Items]
Payment for option exercise	$ 26