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Share-Based Compensation - Summary of Share-Based Compensation (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Share-based compensation $ 10.7 $ 9.4  
Tax benefit 2.7 $ 3.6  
Compensation expense related to share-based compensation $ 89.7   $ 63.5
Weighted average period over which compensation expense will be recognized 2 years