Revenues - Summary of Transaction Price and Allocation of Transaction Price to the Performance Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2025	Jun. 30, 2025	Dec. 31, 2024	Jan. 31, 2024
Disaggregation of Revenue [Line Items]
Premium from Third Stock Purchase Agreement Amendment			$ 87	$ 87
Option continuation payment received in the third quarter of 2024			100	100
Deferred revenue as of January 2024			335	335
Total transaction price	$ 78		319	$ 522
Total transaction price	256	$ 256	522
License and development services
Disaggregation of Revenue [Line Items]
Total transaction price	192		378
Development services
Disaggregation of Revenue [Line Items]
Total transaction price	17		33
Access rights and option continuation periods
Disaggregation of Revenue [Line Items]
Total transaction price	30		77
Rights to certain studies
Disaggregation of Revenue [Line Items]
Total transaction price	17		$ 34
Taiho Pharmaceutical Co., Ltd
Disaggregation of Revenue [Line Items]
Total transaction price	15
Taiho Pharmaceutical Co., Ltd | License
Disaggregation of Revenue [Line Items]
Total transaction price	7
Taiho Pharmaceutical Co., Ltd | R&D services
Disaggregation of Revenue [Line Items]
Total transaction price	$ 8