Income taxes - Uncertain tax positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, January 1	$ 82	$ 69	$ 89
Additions based on tax positions related to the current year	3	3	2
Additions for tax positions of prior years	0	10	7
Reductions for tax positions of prior years	(3)	0	(6)
Settlements with tax authorities	0	0	(23)
Expiration of the statute of limitations for assessing taxes	0	0	0
Balance, December 31	82	82	69
Interest expense recognized in the year ended December 31	(9)	(1)	(5)
Interest payable as of December 31	$ 10	$ 3	$ 13