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Revenue - (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Concentration Risk [Line Items]      
Remaining performance obligation $ 23    
Contract liability 57 $ 62  
Revenue recognized $ 52 $ 60  
Customer Concentration Risk | Revenue Benchmark      
Concentration Risk [Line Items]      
Concentration risk percentage 12.00% 14.00% 15.00%