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Employee Stock-based Compensation Plans Summary of Stock Option Activity (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Shares Under Option    
Outstanding at beginning of period (in shares) 6,509  
Granted (in shares) 10  
Exercised (in shares) (746)  
Canceled (in shares) (153)  
Forfeited (in shares) (247)  
Outstanding at end of period (in shares) 5,373 6,509
Fully vested and expected to vest at period end (in shares) 5,373  
Exercisable at period end (in shares) 4,220  
Weighted-Average Exercise Price per Share    
Outstanding at beginning of period (in usd per share) $ 36.22  
Granted (in usd per share) 29.04  
Exercised (in usd per share) 25.28  
Canceled (in usd per share) 46.56  
Forfeited (in usd per share) 32.97  
Outstanding at end of period (in usd per share) 37.63 $ 36.22
Fully vested and expected to vest at period end (in usd per share) 37.63  
Exercisable at period end (in usd per share) $ 39.60  
Weighted-Average Remaining Contractual Term    
Weighted-average remaining contractual term (in years) 4 years 6 months 5 years 3 months 18 days
Fully vested and expected to vest at period end (in years) 4 years 6 months  
Exercisable at period end (in years) 3 years 4 months 24 days  
Aggregate Intrinsic Value    
Aggregate Intrinsic Value $ 30 $ 8
Fully vested and expected to vest at period end 30  
Exercisable at period end $ 21