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Stock-Based Compensation - Summary (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total stock-based compensation expense $ 12 $ 13
Employee stock option    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total stock-based compensation expense 0 1
Restricted stock and unit awards    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total stock-based compensation expense $ 12 $ 12