Income taxes - Uncertain tax positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, January 1	$ 89	$ 303	$ 286
Additions based on tax positions related to the current year	2	3	3
Additions for tax positions of prior years	7	35	63
Reductions for tax positions of prior years	(6)	(249)	(41)
Settlements with tax authorities	(23)	0	(8)
Expiration of the statute of limitations for assessing taxes	0	(3)	0
Balance, December 31	69	89	303
Interest income (expense) recognized in the year ended December 31	(5)	39	9
Interest payable as of December 31	$ 13	$ 8	$ 44