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Stockholders' Equity - Additional Information (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares available for grant (in shares) 12,000,000  
Aggregate intrinsic value of stock options outstanding $ 35 $ 41
Stock repurchased during period (in shares) 594,799  
Stock repurchased during period $ 30  
Amount available for further repurchases under stock repurchase program $ 106  
PRSAs | Tranche 1    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting percentage 50.00%