Leases - Supplemental Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets
Operating lease assets	$ 111	$ 0
Finance lease assets	19
Total leased assets	130
Current
Operating	32
Finance	9
Non-current
Operating	86	$ 0
Finance	6
Total lease liabilities	$ 133
Weighted-average remaining lease term (years)
Operating leases	5 years 3 months 18 days
Finance leases	4 years 3 months 18 days
Weighted-average discount rate
Operating leases	7.52%
Finance leases	4.73%