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Employee Stock-based Compensation Plans Stock-Based Compensation Expense (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Stock options $ 9 $ 9 $ 12
Restricted shares 56 51 41
Employee share repurchase program 3 2 3
Total stock-based compensation before income taxes 68 62 56
Tax benefit (21) (13) (17)
Total stock-based compensation, net of tax $ 47 $ 49 $ 39