License and Collaborations - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2017	Dec. 31, 2022
License And Collaboration Agreements [Line Items]
Total revenues	$ 32,000,000	$ 33,000,000	$ 86,000,000	$ 78,000,000
Other noncurrent liabilities	145,000,000		145,000,000			$ 140,000,000
Other noncurrent assets ($6 and $2 from a related party)	108,000,000		108,000,000			114,000,000
AstraZeneca Agreement
License And Collaboration Agreements [Line Items]
Development cost recorded within research and development expenses	1,000,000	1,000,000	6,000,000	3,000,000
Other noncurrent liabilities	11,000,000		11,000,000			5,000,000
Gilead Collaboration Agreement
License And Collaboration Agreements [Line Items]
Total revenues			1,000,000
Other noncurrent assets ($6 and $2 from a related party)	6,000,000		6,000,000			$ 2,000,000
Taiho Pharmaceutical Co., Ltd | Taiho Agreement
License And Collaboration Agreements [Line Items]
Option period					5 years
Non refundable and non creditable cash payments					$ 35,000,000
Payment for option exercise	$ 28,000,000
Royalties payable term	10 years
Total revenues	$ 4,000,000	2,000,000	4,000,000	5,000,000
Reimbursement of research and development expense	2,000,000		4,000,000
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Minimum
License And Collaboration Agreements [Line Items]
Payment for option exercise					3,000,000
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Maximum
License And Collaboration Agreements [Line Items]
Payment for option exercise					15,000,000
Additional clinical and regulatory milestone payments receivable					130,000,000
Contingent milestone payments receivable					$ 145,000,000
WuXi Biologics License Agreement | anti-CD39 | Research and Development
License And Collaboration Agreements [Line Items]
Development milestone expense	$ 0	$ 0	1,000,000	$ 2,000,000
WuXi Biologics License Agreement | Maximum | anti-PD-1
License And Collaboration Agreements [Line Items]
Clinical, regulatory and commercialization milestone payments			375,000,000
WuXi Biologics License Agreement | Maximum | anti-CD39
License And Collaboration Agreements [Line Items]
Additional clinical, regulatory and commercialization milestone payments			14,000,000
Abmuno License Agreement
License And Collaboration Agreements [Line Items]
Additional clinical, regulatory and commercialization milestone payments			$ 88,000,000