Summary of Significant Accounting Policies - Performance Obligation (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Remaining performance obligation	$ 5,180	$ 5,300
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Percent of remaining performance obligation expected to be recognized		59.50%
Recognition period for remaining performance obligation		12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Percent of remaining performance obligation expected to be recognized	61.00%
Recognition period for remaining performance obligation	12 months