Revenue - Schedule of Remaining Performance Obligations (Details) $ in Millions	Sep. 30, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Remaining Performance Obligation	$ 1,185
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-07-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Remaining Performance Obligation	$ 124
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Remaining Performance Obligation	$ 392
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Remaining Performance Obligation	$ 669
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period