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Stock-Based Compensation (Narrative) (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 6 $ 7 $ 18 $ 18
Stock-based compensation expense (net of tax) $ 5 $ 5 $ 14 $ 14