Income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income taxes
U.S.	$ (69)	$ 77	$ (806)
Non-U.S			(117)
(Loss) income before taxes	(69)	77	(923)
Current tax (benefit) expense
U.S.	(5)	5
Total	(5)	5
Deferred tax benefit
U.S.	(17)		(2)
Non-U.S.			(46)
Total	(17)		(48)
Income tax (benefit) expense	$ (22)	$ 5	$ (48)