Summary of Significant Accounting Policies and Other Matters - Revenue Recognition, Remaining Performance Obligation (Details) $ in Millions	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Remaining performance obligation	$ 95
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Accounting Policies [Abstract]
Remaining performance obligation	$ 59
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Accounting Policies [Abstract]
Remaining performance obligation	$ 36
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction