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Share-Based Compensation - Summary of Share-Based Compensation (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]          
Share-based compensation $ 8.4 $ 7.0 $ 25.5 $ 22.2  
Tax benefit 3.2 $ 2.7 9.8 $ 8.5  
Compensation expense related to share-based compensation $ 79.3   $ 79.3   $ 56.8
Weighted average period over which compensation expense will be recognized     3 years