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Summary of Significant Accounting Policies - Performance Obligation (Details) - USD ($)
$ in Millions
Mar. 31, 2021
Dec. 31, 2020
Accounting Policies [Abstract]    
Remaining performance obligation $ 4,130 $ 3,990
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   71.20%
Recognition period for remaining performance obligation   12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Percent of remaining performance obligation expected to be recognized 76.70%  
Recognition period for remaining performance obligation 12 months