Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Equity award programs	Purchase Agreement Gilead	Common Stock	Common Stock Equity award programs	Common Stock Purchase Agreement Gilead	Common stock and additional paid-in-capital	Common stock and additional paid-in-capital Equity award programs	Common stock and additional paid-in-capital Purchase Agreement Gilead	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2019	$ 164						$ 369			$ (205)
Balance, shares at Dec. 31, 2019				44,200,000
Issuance of common stock	326	$ 6	$ 107				326	$ 6	$ 107
Issuance of common stock, shares			6,000,000.0	12,700,000	800,000	6,000,000.0
Stock-based compensation	22						22
Net income (loss)	(123)									(123)
Balance at Dec. 31, 2020	502						830			(328)
Balance, shares at Dec. 31, 2020				63,700,000
Issuance of common stock		13	$ 220					13	$ 220
Issuance of common stock, shares					1,400,000	5,700,000
Stock-based compensation	55						55
Other comprehensive income (loss)	(1)										$ (1)
Net income (loss)	53									53
Balance at Dec. 31, 2021	$ 842						1,118			(275)	(1)
Balance, shares at Dec. 31, 2021	70,800,000			70,800,000
Issuance of common stock		$ 23						$ 23
Issuance of common stock, shares					2,100,000
Stock-based compensation	$ 65						65
Other comprehensive income (loss)	(6)										(6)
Net income (loss)	(267)									(267)
Balance at Dec. 31, 2022	$ 657						$ 1,206			$ (542)	$ (7)
Balance, shares at Dec. 31, 2022	72,900,000			72,900,000