Revenue Recognition - Performance Obligations (Details) $ in Millions	Jun. 30, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Remaining performance obligation amount	$ 502
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation amount	$ 169
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of remaining performance obligation, period	6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation amount	$ 104
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of remaining performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation amount	$ 229
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of remaining performance obligation, period