Revenue - Unsatisfied Performance Obligations (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01 $ in Millions	Dec. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligation	$ 530
Unsatisfied performance obligation, period of recognition	3 years