Revenues - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract payment period			15 days
Remaining performance obligations	$ 0		$ 0
Contract assets	0		0
Contract liability	0		0
Deferred contract costs	0		0
Impairment losses	$ 0	$ 0	$ 0	$ 0
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transit time			3 days
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transit time			8 days