License and Collaborations - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended		12 Months Ended
	Jan. 31, 2025	Oct. 31, 2024	Jul. 31, 2024	Sep. 30, 2024	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020	Dec. 31, 2017
License and Collaboration Agreements [Line Items]
Licensing revenue recognized						$ 243	$ 108	$ 112
Total revenues						51	37	38
Receivable from collaboration partners, current						20	38
Other noncurrent assets						73	106
Other current liabilities						123	76
Other noncurrent liabilities						157	142
Taiho Collaboration Agreement
License and Collaboration Agreements [Line Items]
Milestone payments		$ 19
Receivable from collaboration partners, current						14	18
Other liabilities						36
AstraZeneca Agreement
License and Collaboration Agreements [Line Items]
Milestone payments									$ 24
Other liabilities						26
Development cost recorded within research and development expenses						14	6	4
Other noncurrent liabilities							11
Gilead Collaboration Agreement
License and Collaboration Agreements [Line Items]
Other noncurrent assets							6
Development cost recorded within research and development expenses						6
Taiho Pharmaceutical Co., Ltd | Taiho Agreement
License and Collaboration Agreements [Line Items]
Option period										5 years
Non refundable and non creditable cash payments										$ 35
Payment for option exercise			$ 15	$ 15		15
Royalties payable term										10 years
Total revenues						15	5	5
Reimbursement of research and development expense						28	8
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Minimum
License and Collaboration Agreements [Line Items]
Payment for option exercise										$ 3
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Maximum
License and Collaboration Agreements [Line Items]
Payment for option exercise										15
Additional clinical and regulatory milestone payments receivable										130
Contingent milestone payments receivable										$ 145
STAR-221 Development Activities | Taiho Collaboration Agreement
License and Collaboration Agreements [Line Items]
Payment for option exercise							28
STAR-121 Development Activities | Taiho Collaboration Agreement
License and Collaboration Agreements [Line Items]
Payment for option exercise					$ 26
Licensing revenue recognized					$ 16
STAR-121 Development Activities | Taiho Collaboration Agreement | Subsequent Event
License and Collaboration Agreements [Line Items]
Licensing revenue recognized	$ 10
WuXi Biologics License Agreement | anti-CD39 | Research and Development
License and Collaboration Agreements [Line Items]
Milestone payments							$ 1	2
WuXi Biologics License Agreement | Maximum | anti-PD-1
License and Collaboration Agreements [Line Items]
Clinical regulatory milestone payments						50
Commercialization milestone payments						375
WuXi Biologics License Agreement | Maximum | anti-CD39
License and Collaboration Agreements [Line Items]
Additional clinical, regulatory and commercialization milestone payments						14
Abmuno License Agreement
License and Collaboration Agreements [Line Items]
Additional clinical, regulatory and commercialization milestone payments						$ 88
Abmuno License Agreement | Research and Development
License and Collaboration Agreements [Line Items]
Development milestone expense								$ 5