Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities
Net loss	$ (226)	$ (200)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense	55	48
Depreciation and amortization	5	5
Noncash lease expense	6	6
Amortization of premiums (discounts) on marketable securities	(13)	2
Other items, net	2	3
Changes in operating assets and liabilities:
Receivable from collaboration partners ($17 and $718 from a related party)	15	716
Other assets (($4) and ($2) from a related party)	(12)	(4)
Accounts payable	(3)	0
Deferred revenue (($47) and ($73) to a related party)	(51)	(78)
Other liabilities	4	10
Net cash provided by (used in) operating activities	(218)	508
Cash flows from investing activities
Purchases of marketable securities	(673)	(1,085)
Proceeds from maturities of marketable securities	837	491
Proceeds from sales of marketable securities	20	143
Purchases of property and equipment	(18)	(6)
Purchases of in-process research and development	0	(6)
Collaboration reimbursements of in-process research and development	0	3
Net cash provided by (used in) investing activities	166	(460)
Cash flows from financing activities
Proceeds from issuance of common stock ($20 and $— from a related party)	25	0
Proceeds from issuance of common stock pursuant to equity award plans	5	17
Proceeds from sale of future royalties	0	5
Net cash provided by financing activities	30	22
Net increase (decrease) in cash, cash equivalents and restricted cash	(22)	70
Cash, cash equivalents and restricted cash at beginning of period	209	151
Cash, cash equivalents and restricted cash at end of period	187	221
Non-cash investing and financing activities:
Unpaid portion of property and equipment purchases included in Accounts payable and Other current liabilities	$ 6	$ 1