License and Collaborations - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Sep. 30, 2024	Mar. 31, 2024	Dec. 31, 2022	Dec. 31, 2020	Dec. 31, 2017	Dec. 31, 2024	Dec. 31, 2023
License And Collaboration Agreements [Line Items]
Total revenues		$ 8		$ 10
Receivable from collaboration partners, current		15						$ 20
Other noncurrent assets		71						73
Other current liabilities		98						123
Other noncurrent liabilities		166						157
Taiho Collaboration Agreement
License And Collaboration Agreements [Line Items]
Milestone payments		12	$ 19
Receivable from collaboration partners, current		10						14
Other liabilities		49						36
Taiho Collaboration Agreement | Forecast
License And Collaboration Agreements [Line Items]
Milestone payments	$ 7
AstraZeneca Agreement
License And Collaboration Agreements [Line Items]
Milestone payments						$ 24
Development cost recorded within research and development expenses		4		3
Other current liabilities		16
Other noncurrent liabilities								$ 26
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
Royalties payable term							10 years
Total revenues				4
Reimbursement of research and development expense		9		3
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]
Milestone payments					$ 28
STAR-121 Development Activities | Taiho Collaboration Agreement
License And Collaboration Agreements [Line Items]
Milestone payments		10		16	$ 26
WuXi Biologics License Agreement | anti-PD-1
License And Collaboration Agreements [Line Items]
Development milestone expense		0		0
WuXi Biologics License Agreement | anti-CD39
License And Collaboration Agreements [Line Items]
Development milestone expense		0		0
WuXi Biologics License Agreement | Maximum | anti-PD-1
License And Collaboration Agreements [Line Items]
Clinical regulatory milestone payments		50
Clinical, regulatory and 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]
Development milestone expense		0		$ 0
Additional clinical, regulatory and commercialization milestone payments		$ 88