Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Second Stock Purchase Agreement Gilead	Equity Award Programs	Common Stock	Common Stock Second Stock Purchase Agreement Gilead	Common Stock Equity Award Programs	Common stock and additional paid-in capital	Common stock and additional paid-in capital Second Stock Purchase Agreement Gilead	Common stock and additional paid-in capital Equity Award Programs	Accumulated deficit	Accumulated other comprehensive loss
Beginning balance, shares at Dec. 31, 2021				70.8
Beginning balance at Dec. 31, 2021	$ 842						$ 1,118			$ (275)	$ (1)
Issuance of common stock (in shares)						0.8
Issuance of common stock			$ 10						$ 10
Stock-based compensation	17						17
Other comprehensive gain (loss)	(4)										(4)
Net loss	(68)									(68)
Ending balance, shares at Mar. 31, 2022				71.6
Ending balance at Mar. 31, 2022	797						1,145			(343)	(5)
Beginning balance, shares at Dec. 31, 2021				70.8
Beginning balance at Dec. 31, 2021	842						1,118			(275)	(1)
Net loss	(200)
Ending balance, shares at Sep. 30, 2022				72.4
Ending balance at Sep. 30, 2022	699						1,183			(475)	(9)
Beginning balance, shares at Mar. 31, 2022				71.6
Beginning balance at Mar. 31, 2022	797						1,145			(343)	(5)
Issuance of common stock (in shares)						0.5
Issuance of common stock			4						4
Stock-based compensation	15						15
Other comprehensive gain (loss)	(2)										(2)
Net loss	(67)									(67)
Ending balance, shares at Jun. 30, 2022				72.1
Ending balance at Jun. 30, 2022	747						1,164			(410)	(7)
Issuance of common stock (in shares)						0.3
Issuance of common stock			3						3
Stock-based compensation	16						16
Other comprehensive gain (loss)	(2)										(2)
Net loss	(65)									(65)
Ending balance, shares at Sep. 30, 2022				72.4
Ending balance at Sep. 30, 2022	$ 699						1,183			(475)	(9)
Beginning balance, shares at Dec. 31, 2022	72.9			72.9
Beginning balance at Dec. 31, 2022	$ 657						1,206			(542)	(7)
Issuance of common stock (in shares)						0.2
Issuance of common stock			1						1
Stock-based compensation	19						19
Other comprehensive gain (loss)	3										3
Net loss	(80)									(80)
Ending balance, shares at Mar. 31, 2023				73.1
Ending balance at Mar. 31, 2023	$ 600						1,226			(622)	(4)
Beginning balance, shares at Dec. 31, 2022	72.9			72.9
Beginning balance at Dec. 31, 2022	$ 657						1,206			(542)	(7)
Net loss	$ (226)
Ending balance, shares at Sep. 30, 2023	74.8			74.8
Ending balance at Sep. 30, 2023	$ 520						1,291			(768)	(3)
Beginning balance, shares at Mar. 31, 2023				73.1
Beginning balance at Mar. 31, 2023	600						1,226			(622)	(4)
Issuance of common stock (in shares)					1.0	0.4
Issuance of common stock		$ 20	3					$ 20	3
Stock-based compensation	18						18
Net loss	(75)									(75)
Ending balance, shares at Jun. 30, 2023				74.5
Ending balance at Jun. 30, 2023	566						1,267			(697)	(4)
Issuance of common stock (in shares)				0.2		0.1
Issuance of common stock	5		$ 1				5		$ 1
Stock-based compensation	18						18
Other comprehensive gain (loss)	1										1
Net loss	$ (71)									(71)
Ending balance, shares at Sep. 30, 2023	74.8			74.8
Ending balance at Sep. 30, 2023	$ 520						$ 1,291			$ (768)	$ (3)