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Stock-Based Compensation - Annual Activity Of Stock Options (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Aggregate Intrinsic Value - Exercised $ 1 $ 8 $ 21