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Share-Based Compensation - Additional Information (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Total fair value of share-based compensation awards vested $ 59.4 $ 20.7 $ 27.4
Excess tax benefit recognized from share-based incentive plans 10.9 5.1  
Total compensation cost not yet recognized $ 63.5 $ 66.4  
Weighted average period for recognition (in years) 2 years