Commitments and Contingencies - Environmental Matters (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Portion of environmental remediation costs recorded in other current liabilities	$ 10	$ 12
Portion of environmental remediation costs recorded in deferred credits and other liabilities	29	28
Environmental remediation accrual, discounted basis	$ 39	$ 40
Weighted average discount rate	1.70%	2.90%
Expected payments of environmental remediation costs, 2019	$ 8
Expected payments of environmental remediation costs, 2020	6
Expected payments of environmental remediation costs, 2021	3
Expected payments of environmental remediation costs, 2022	2
Expected payments of environmental remediation costs, 2023	2
Expected payments of environmental remediation costs, thereafter	$ 17