Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended	51 Months Ended
	Mar. 31, 2019	Dec. 31, 2015	Mar. 31, 2019
Consent Decree
Other Commitments [Line Items]
Consent decree		$ 5	$ 84
Mitigation projects	$ 5
Supplemental environmental projects	$ 4
Consent Decree - Corrective Actions At Certain Tank Systems
Other Commitments [Line Items]
Consent decree			$ 78