Contingencies and commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating leases and other obligations
2019	$ 25
2020	22
2021	22
2022	20
2023	20
Thereafter	99
Total operating leases	208
Capital lease commitments
2019	7
2020	4
2021	2
Total capital leases	13
Total lease expenses	36	$ 37	$ 33
Capital lease obligations net	$ 10	$ 12