Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues:
Total revenues	$ 117	$ 112	$ 383
Operating expenses:
Research and development (Net of recoveries of $110, $132 and $25 from a related party)	340	288	257
General and administrative (Net of recoveries of $—, $1 and $— from a related party)	117	104	72
Total operating expenses	457	392	329
Income (loss) from operations	(340)	(280)	54
Non-operating income (expense):
Interest and other income, net	41	16	1
Effective interest on liability for sale of future royalties	(2)	(2)	0
Total non-operating income, net	39	14	1
Income (loss) before income taxes	(301)	(266)	55
Income tax expense	(6)	(1)	(2)
Net income (loss)	$ (307)	$ (267)	$ 53
Net income (loss) per share, basic (in dollars per share)	$ (4.15)	$ (3.71)	$ 0.76
Net income (loss) per share, diluted (in dollars per share)	$ (4.15)	$ (3.71)	$ 0.71
Shares used to compute net income (loss) per share, basic (in shares)	74.0	72.0	69.3
Shares used to compute net income (loss) per share, diluted (in shares)	74.0	72.0	74.0
License and Development Services Revenue
Revenues:
Total revenues	$ 80	$ 74	$ 345
Other Collaboration Revenue
Revenues:
Total revenues	$ 37	$ 38	$ 38