Revenues - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	May 31, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				$ 32	$ 33	$ 86	$ 78
Contract with customer, liability	$ 429			429		429
Total allocated transaction price						35
Deferred revenue recognized				28	33	79	78
Gilead Collaboration Agreement
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax						1
Contract with customer, liability								$ 452
R&D Activities for Domvanalimab
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				1		3	2
Contract with customer, liability	27			27		27
Deferred revenue recognized						34
R&D and Commercialization Activities for Zimberelimab
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				0	8	1	9
Deferred revenue recognized						11
Access Rights and Option Continuation Periods
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				8	8	25	25
Contract with customer, liability	62			62		62
Gilead
Disaggregation of Revenue [Line Items]
Capitalized contract cost, amortization						1	1
Cost sharing receivable	3			3		3
Gilead | Prepaid Expenses and Other Current Assets
Disaggregation of Revenue [Line Items]
Capitalized contract cost, net, current	1			1		1
Gilead | Other Noncurrent Assets
Disaggregation of Revenue [Line Items]
Capitalized contract cost, net, noncurrent	2			2		2
Gilead | Gilead Collaboration Agreement
Disaggregation of Revenue [Line Items]
Upfront cash payment		$ 35
Total allocated transaction price			$ 35
Deferred revenue recognized						$ 121
Current and future programs exclusive access period						10 years
Contingent milestone payments receivable	300			300		$ 300
Option continuation payment receivable upon sixth anniversary of agreement	100			100		$ 100
Performance obligation period						4 years
Gilead | R&D Activities for Inflammation Programs
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				2		$ 3
Contract with customer, liability	32			32		32
Gilead | Etrumadenant License and research and Development Services Agreement
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				21	3	39	21
Contract with customer, liability	146			146		146
Deferred revenue recognized						219
Gilead | Quemliclustat, License and R&D services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				(4)	$ 12	11	$ 16
Contract with customer, liability	138			$ 138		138
Deferred revenue recognized						$ 176
Gilead | Revenue Benchmark | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percentage of revenues				88.00%	94.00%	95.00%	94.00%
STAR-221 Development Activities | Taiho Collaboration Agreement
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax				$ 4		$ 4
Contract with customer, liability	24			$ 24		$ 24
Revenue recognized	$ 28