Leases - Operating Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 12	$ 24
Amortization of right-of-use assets	4	9
Interest on lease liabilities	2	4
Total finance lease cost	6	13
Total lease cost	18	37
Short-term lease costs	2	6
Vehicles
Lessee, Lease, Description [Line Items]
Operating lease costs	8	15
Amortization of right-of-use assets	4	8
Interest on lease liabilities	1	2
Total finance lease cost	5	10
Total lease cost	13	25
Buildings
Lessee, Lease, Description [Line Items]
Operating lease costs	1	3
Amortization of right-of-use assets	0	0
Interest on lease liabilities	1	2
Total finance lease cost	1	2
Total lease cost	2	5
Other
Lessee, Lease, Description [Line Items]
Operating lease costs	3	6
Amortization of right-of-use assets	0	1
Interest on lease liabilities	0	0
Total finance lease cost	0	1
Total lease cost	$ 3	$ 7