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Description of Business and Significant Accounting Policies - Narrative (Details)
$ in Millions
1 Months Ended 9 Months Ended
Apr. 30, 2020
Sep. 30, 2020
USD ($)
segment
Dec. 31, 2019
USD ($)
Product Information [Line Items]      
Number of reportable segments | segment   1  
Eligible period for one-time fee reduction program 2 years    
Unsatisfied performance obligations   $ 104  
Advance collections of unbilled revenues   71  
Prepayments offsetting accrued health insurance costs   $ 46 $ 39
Non-US | Revenue | Foreign Sales      
Product Information [Line Items]      
Percent of concentration risk (less than)   1.00%  
Health Care      
Product Information [Line Items]      
Prepayments offsetting accrued health insurance costs   $ 59 $ 52