Leases - Maturity Analysis of Finance and Operating Lease Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Finance Leases, After Adoption of 842:
2019 remaining	$ 7
2020	10
2021	10
2022	0
2023	0
Thereafter	0
Total lease payments	27
Less imputed interest	(3)
Present value of lease liabilities	24
Less current maturities	(9)
Present value of lease liabilities, less current maturities	15
Operating Leases, After Adoption of 842:
2019 remaining	18
2020	6
2021	2
2022	2
2023	2
Thereafter	7
Total lease payments	37
Less imputed interest	(3)
Present value of lease liabilities	34
Less current maturities	(19)
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