Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Detail)

v3.8.0.1
Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
SARs [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Awards Outstanding, Beginning Balance 11,998  
Granted, Awards 1,362  
Exercised, Awards (3,394)  
Forfeited, Awards (369)  
Awards Outstanding, Ending Balance 9,597 11,998
Exercisable Awards, Ending Balance 5,438  
Weighted Average Exercise Price Outstanding, Beginning Balance $ 41.52  
Granted, Weighted Average Exercise Price 57.33  
Exercised, Weighted Average Exercise Price 31.86  
Forfeited, Weighted Average Exercise Price 53.59  
Weighted Average Exercise Price Outstanding, Ending Balance 46.72 $ 41.52
Exercisable, Weighted Average Exercise Price, Ending Balance $ 46.30  
Weighted Average Remaining Contractual Term Outstanding 6 years 2 months 12 days 6 years
Exercisable Weighted Average Remaining Contractual Term 4 years 9 months 18 days  
Aggregate Intrinsic Value Outstanding $ 212.0 $ 148.7
Exercisable, Aggregate Intrinsic Value $ 126.9  
Incentive Plan and Independent Directors Stock Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding and nonvested as of December 31, 2016, Shares 26  
Granted, Shares 162  
Vested, Shares (25)  
Outstanding and nonvested as of December 31, 2017, Shares 163 26
Outstanding and nonvested as of December 31, 2016, Weighted Average Grant Date Fair Value $ 62.35  
Granted, Weighted Average Grant Date Fair Value 68.74  
Vested, Weighted Average Grant Date Fair Value 62.40  
Outstanding and nonvested as of December 31, 2017, Weighted Average Grant Date Fair Value $ 68.69 $ 62.35