Leases - Maturity Analysis of Finance and Operating Lease Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Finance Leases, After Adoption of 842:
Remainder of 2019	$ 5
2020	10
2021	10
2022	0
2023	0
Thereafter	0
Total lease payments	25
Less imputed interest	(3)
Present value of lease liabilities	22
Less current maturities	(9)
Present value of lease liabilities, less current maturities	13
Operating Leases, After Adoption of 842:
Remainder of 2019	8
2020	8
2021	3
2022	2
2023	2
Thereafter	7
Total lease payments	30
Less imputed interest	(3)
Present value of lease liabilities	27
Less current maturities	(12)
Present value of lease liabilities, less current maturities	$ 15
Capital Leases, Before Adoption of 842:
2019		$ 10
2020		10
2021		10
Total minimum lease payments		30
Operating Leases, After Before of 842:
2019		3
2020		1
2021		0
Total minimum lease payments		$ 4