Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues:
Total revenues	$ 258	$ 117	$ 112
Operating expenses:
Research and development (Includes $39, $110 and $132 of net recoveries from a related party)	448	340	288
General and administrative (Includes ($2), $— and $1 of net recoveries from (payments to) a related party)	120	117	104
Impairment of long-lived assets (see Note 14, Leases)	20	0	0
Total operating expenses	588	457	392
Loss from operations	(330)	(340)	(280)
Non-operating income (expense):
Interest and other income, net	52	41	16
Interest expense	(4)	(2)	(2)
Total non-operating income, net	48	39	14
Loss before income taxes	(282)	(301)	(266)
Income tax expense	(1)	(6)	(1)
Net loss	$ (283)	$ (307)	$ (267)
Net loss per share, basic (in dollars per share)	$ (3.14)	$ (4.15)	$ (3.71)
Net loss per share, diluted (in dollars per share)	$ (3.14)	$ (4.15)	$ (3.71)
Shares used to compute net loss per share, basic (in shares)	90.1	74.0	72.0
Shares used to compute net loss per share, diluted (in shares)	90.1	74.0	72.0
License and Development Services Revenue
Revenues:
Total revenues	$ 222	$ 80	$ 74
Other Collaboration Revenue
Revenues:
Total revenues	$ 36	$ 37	$ 38