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Summary of Nonvested Restricted Stock Unit Awards (Detail) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
WEIGHTED AVERAGE REMAINING VESTING TERM (YEARS)    
Nonvested 2 years 1 year 10 months 24 days
Restricted Stock Unit Awards    
NUMBER    
Beginning Balance (in shares) 3,222,219  
Granted (in shares) 1,301,693  
Vested (in shares) (923,050)  
Forfeited (in shares) (85,230)  
Ending Balance (in shares) 3,515,632 3,222,219
WEIGHTED AVERAGE GRANT-DATE FAIR VALUE PER UNIT    
Nonvested at beginning of year (in dollars per share) $ 59.50  
Granted (in dollars per share) 59.17  
Vested (in dollars per share) 50.02  
Forfeited (in dollars per share) 62.30  
Nonvested at end of year (in dollars per share) $ 61.80 $ 59.50