Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash flows from operating activities
Net loss	$ (80)	$ (68)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	19	17
Depreciation and amortization	2	1
Noncash lease expense	2	2
Amortization of premiums (discounts) on marketable securities	(4)	2
Other items, net	1	3
Changes in operating assets and liabilities:
Receivable from collaboration partners ($6 and $715 from a related party)	6	715
Other assets (($1) and ($1) from a related party)	(8)	(7)
Accounts payable	10	8
Deferred revenue (($25) and ($16) to a related party)	(25)	(18)
Other liabilities	(21)	(1)
Net cash provided by (used in) operating activities	(98)	654
Cash flows from investing activities
Purchases of marketable securities	(154)	(377)
Proceeds from maturities of marketable securities	284	94
Proceeds from sales of marketable securities	2	18
Purchases of property and equipment	(3)	(3)
Net cash provided by (used in) investing activities	129	(268)
Cash flow from financing activities
Proceeds from issuance of common stock pursuant to equity award plans	1	10
Proceeds from sale of future royalties		5
Net cash provided by financing activities	1	15
Net increase in cash, cash equivalents and restricted cash	32	401
Cash, cash equivalents and restricted cash at beginning of period	209	151
Cash, cash equivalents and restricted cash at end of period	241	552
Non-cash investing and financing activities:
Unpaid portion of property and equipment purchases included in accounts payable and accrued liabilities	$ 4	1
Unpaid acquisition of in-process research and development		$ 3