Revenue Recognition Remaining Performance Obligations (Details) $ in Millions	Sep. 30, 2018 USD ($)
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 867
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 144
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 234
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
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
Revenue Recognition and Deferred Revenue [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 182
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year