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Stock Options (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant-date fair value of all stock options that vested   $ 8 $ 18
Intrinsic value of all stock options exercised $ 172 $ 265 $ 297