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Share-Based Compensation - Summary of Share-Based Compensation (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Share-based compensation $ 8.0us-gaap_AllocatedShareBasedCompensationExpense $ 6.5us-gaap_AllocatedShareBasedCompensationExpense  
Tax benefit 3.1us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 2.5us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense  
Share-based Compensation [Abstract]      
Compensation expense related to share-based compensation $ 95.9us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized   $ 56.8us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Weighted average period over which compensation expense will be recognized 3 years