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Share Plans - Additional Information (Detail) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Mar. 31, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based Compensation $ 6.2   $ 6.4 $ 32.2 $ 28.7
2012 Stock and Incentive Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of stock options and restricted stock units issued under stock and incentive plan   1.4      
Restricted Stock Units (RSUs) [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based Compensation 2.9   3.6 14.4 14.2
Restricted Stock Units (RSUs) [Member] | 2012 Stock and Incentive Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of restricted stock units issued under stock and incentive plan   0.3      
Weighted-average fair value of restricted stock units granted   $ 58.93      
Equity Option [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based Compensation 1.9   1.8 8.3 9.0
Equity Option [Member] | 2012 Stock and Incentive Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross   0.9      
Weighted-average fair value of options granted   $ 12.57      
Performance Shares [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based Compensation $ 1.4   $ 1.0 $ 9.5 $ 5.5
Performance Shares [Member] | 2012 Stock and Incentive Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of restricted stock units issued under stock and incentive plan   0.2      
Weighted-average fair value of restricted stock units granted   $ 58.41