License and Collaborations - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended			6 Months Ended		12 Months Ended
	Jul. 31, 2024	Jan. 31, 2024	Mar. 31, 2025	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2020	Dec. 31, 2017	Dec. 31, 2023
License And Collaboration Agreements [Line Items]
Revenue recognized from amounts in deferred revenue at the beginning of the period				$ 39	$ 28	$ 180	$ 53
Total revenues				39	29	184	54
Receivable from collaboration partners ($14 and $20 from a related party)				28		28				$ 38
Other noncurrent assets ($— and $6 from a related party)				75		75				106
Other current liabilities				71		71				76
Other noncurrent liabilities				138		138				142
Research and development (Includes $14, $34, $30 and $67 of net recoveries from a related party)				115	84	224	165
Taiho Collaboration Agreement
License And Collaboration Agreements [Line Items]
Total revenues				3		7
Receivable from collaboration partners ($14 and $20 from a related party)				14		14				18
AstraZeneca Agreement
License And Collaboration Agreements [Line Items]
Milestone payments								$ 24
Development cost recorded within research and development expenses				4	3	6	5
Other current liabilities				6		6
Other noncurrent liabilities				12		12				11
Gilead Collaboration Agreement
License And Collaboration Agreements [Line Items]
Other noncurrent assets ($— and $6 from a related party)										$ 6
Development cost recorded within research and development expenses						6
Exelixis Collaboration
License And Collaboration Agreements [Line Items]
Research and development (Includes $14, $34, $30 and $67 of net recoveries from a related party)				2		3
Taiho Pharmaceutical Co., Ltd | Taiho Agreement
License And Collaboration Agreements [Line Items]
Option period									5 years
Non refundable and non creditable cash payments									$ 35
Royalties payable term									10 years
Total revenues				3		7
Reimbursement of research and development expense				4	$ 2	7	2
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Subsequent Event
License And Collaboration Agreements [Line Items]
Payment for option exercise	$ 15
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
Revenue recognized from amounts in deferred revenue at the beginning of the period						16
STAR-121 Development Activities | Taiho Collaboration Agreement | Forecast
License And Collaboration Agreements [Line Items]
Revenue recognized from amounts in deferred revenue at the beginning of the period			$ 10
WuXi Biologics License Agreement | anti-CD39 | Research and Development
License And Collaboration Agreements [Line Items]
Development milestone expense				$ 0		0	$ 1
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]
Additional clinical, regulatory and commercialization milestone payments						$ 88