Income taxes - Uncertain tax positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, January 1	$ 85	$ 82	$ 82
Additions based on tax positions related to the current year	2	3	3
Additions for tax positions of prior years	0	0	0
Reductions for tax positions of prior years	0	0	(3)
Balance, December 31	87	85	82
Interest income (expense) recognized in the year ended December 31	9	(5)	(9)
Interest payable as of December 31	$ 22	$ 15	$ 10