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Stock Option Activity (Parenthetical) (Detail) - 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]      
Cash received from options exercised $ 257 $ 221 $ 148
Actual tax benefit realized for the tax deductions from the option exercises $ 31 $ 31 $ 58