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Stock-Based Compensation (Summary Of Share Based Compensation Shares Authorized Under Stock Option Plans By Exercise Price Range) (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price $ 0    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross $ 0    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number 0   57
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price $ 0   $ 0.79
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price $ 0    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value $ 1 $ 7  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period 0    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (57)    
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price $ 0.79    
Options outstanding, intrinsic value $ 0   $ 1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term     1 month 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures 0    
Proceeds from Stock Options Exercised   $ 2