Leases - Supplemental lease balance sheet information (Details) $ in Millions	Mar. 31, 2019 USD ($)
Leases
Non-current operating lease assets	$ 129
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Non-current operating lease assets
Finance	$ 9
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property, Plant and Equipment, Net
Total leased assets	$ 138
Current operating lease liabilities	$ 33
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current operating lease liabilities
Operating lease liability, non current	$ 137
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating lease liability, non current
Finance lease liability, current	$ 3
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current
Finance lease liability, non current	$ 3
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent
Total leased Liabilities	$ 176