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Share-Based Compensation Plans - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Equity awards fair value $ 76.0 $ 80.0 $ 92.0
Outstanding stock option awards 500,000    
Outstanding stock option awards, exercisable 100,000    
Outstanding weighted average exercise price $ 51.67    
Outstanding exercisable weighted average exercise price $ 34.74    
Outstanding intrinsic value $ 8.0    
Outstanding exercisable intrinsic value $ 5.0    
Outstanding weighted average remaining contractual live 6 years 3 months 19 days    
Outstanding exercisable weighted average remaining contractual live 3 years 8 months 12 days    
RSUs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, other than options, awards granted 1,600,000 1,900,000 1,000,000
Liabilities related to share based payments $ 38.0    
Payment related to share-based liabilities $ 50.0 $ 69.0 $ 85.0
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, options, awards granted 36,000    
Share-Based Compensation, options term 10 years    
Percentage of premium of the grant date fair market value   25.00%  
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price $ 77.56 $ 56.19  
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, grant date fair value $ 0.7 $ 2.3  
Stock Options | Exercise Prices Equal to Fair Market Value      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, options, awards granted 36,000.0 100,000 0
Stock Options | Stock options with exercise prices at a 25% premium of the grant date fair market value      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, options, awards granted   300,000  
Time-Vested RSUs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, other than options, awards granted 1,000,000    
Share-Based Compensation, vesting period 3 years    
Number of days used to compute performance period average closing price of restricted stock units 20 days    
Performance-Based RSUs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation, other than options, awards granted 600,000    
Share-Based Compensation, vesting period 3 years    
Number of days used to compute performance period average closing price of restricted stock units 20 days    
Share-Based Compensation, vesting date Dec. 31, 2019