Business segment - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting, Asset Reconciling Item [Line Items]
Total revenues	$ 247	$ 258	$ 117
Adjusted for expense (income):
Impairment of long-lived assets	0	20	0
Interest income, net	8	4	2
Income tax expense	0	1	6
Net loss	(353)	(283)	(307)
Reportable segment
Segment Reporting, Asset Reconciling Item [Line Items]
Total revenues	247	258	117
Adjusted for expense (income):
Late-stage development programs	274	252	168
Early-stage development and preclinical programs	141	132	128
Compensation and personnel costs	245	250	223
Depreciation and amortization	10	10	8
Impairment of long-lived assets	0	20	0
Interest income, net	(33)	(48)	(39)
Income tax expense	0	1	6
Other segment items	90	89	92
Partnership reimbursements	(127)	(165)	(162)
Net loss	$ (353)	$ (283)	$ (307)