Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Cash flows from operating activities
Net loss	$ (155)	$ (135)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	37	32
Depreciation and amortization	4	3
Noncash lease expense	4	4
Amortization of premiums (discounts) on marketable securities	(8)	2
Other items, net	1	4
Changes in operating assets and liabilities:
Receivable from collaboration partners ($7 and $709 from a related party)	4	709
Other assets (($3) and ($1) from a related party)	(1)	3
Accounts payable	(9)	12
Deferred revenue (($19) and ($42) to a related party)	(19)	(45)
Other liabilities	(13)
Net cash provided by (used in) operating activities	(155)	589
Cash flows from investing activities
Purchases of marketable securities	(393)	(763)
Proceeds from maturities of marketable securities	542	263
Proceeds from sales of marketable securities	14	27
Purchases of property and equipment	(8)	(4)
Purchases of in-process research and development		(6)
Net cash provided by (used in) investing activities	155	(483)
Cash flow from financing activities
Proceeds from issuance of common stock to a related party	20
Proceeds from issuance of common stock pursuant to equity award plans	4	14
Proceeds from sale of future royalties		5
Net cash provided by financing activities	24	19
Net increase in cash, cash equivalents and restricted cash	24	125
Cash, cash equivalents and restricted cash at beginning of period	209	151
Cash, cash equivalents and restricted cash at end of period	233	276
Non-cash investing and financing activities:
Unpaid portion of property and equipment purchases included in accounts payable and accrued liabilities	$ 8	$ 1