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Stock-Based Compensation - Summary of stock-based compensation expense (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Income tax benefit related to stock-based compensation expense $ (5) $ (4) $ (4)
Stock-based compensation expense, net of income taxes 8 6 7
Stock-based compensation expense related to modification of awards 4    
Salaries and related expenses | Equity Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 5 9 9
Salaries and related expenses | Liability Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 1 1 2
Exit and disposal costs | Liability Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 7 $ 0 $ 0