Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Outstanding and nonvested as of December 31, 2017, Number of Shares     326,000    
Granted, Number of Shares     1,375,000    
Vested, Number of Shares     (42,000)    
Forfeited, Number of Shares     (41,000)    
Outstanding and nonvested as of September 30, 2018, Number of Shares 1,618,000   1,618,000   326,000
Outstanding and nonvested as of December 31, 2017, Weighted Average Grant Date Fair Value Per Share     $ 34.34    
Granted, Weighted Average Grant Date Fair Value Per Share     43.67    
Vested, Weighted Average Grant Date Fair Value Per Share     35.75    
Forfeited, Weighted Average Grant Date Fair Value Per Share     43.15    
Outstanding and nonvested as of September 30, 2018, Weighted Average Grant Date Fair Value Per Share $ 42.01   $ 42.01   $ 34.34
SARs [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of Awards Outstanding, Beginning Balance     19,193,000    
Granted, Number of Awards 0   0    
Exercised, Number of Awards     (9,919,000)    
Forfeited, Number of Awards     (303,000)    
Number of Awards Outstanding, Ending Balance 8,971,000   8,971,000   19,193,000
Number of Awards Exercisable, Ending Balance 5,654,000   5,654,000    
Weighted Average Exercise Price Per Award Outstanding, Beginning Balance     $ 23.36    
Exercised, Weighted Average Exercise Price Per Award     20.76    
Forfeited, Weighted Average Exercise Price Per Award     28.77    
Weighted Average Exercise Price Per Award Outstanding, Ending Balance $ 26.05   26.05   $ 23.36
Exercisable, Weighted Average Exercise Price Per Award, Ending Balance $ 23.90   $ 23.90    
Weighted Average Remaining Contractual Term Outstanding     6 years 1 month 6 days   6 years 2 months 12 days
Exercisable Weighted Average Remaining Contractual Term     5 years    
Aggregate Intrinsic Value Outstanding $ 255.7   $ 255.7   $ 212.0
Exercisable, Aggregate Intrinsic Value $ 173.3   $ 173.3    
Granted, Weighted Average Grant Date Fair Value Per Share   $ 15.66   $ 14.18