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Share-Based Compensation (Assumptions) (Details) - Options - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-Based Compensation      
Unrecognized compensation cost $ 640.9    
Weighted-average period over which unrecognized compensation cost is expected to be recognized 2 years    
Weighted-average grant date fair value of the stock options issued (in dollars per share) $ 38.83 $ 27.92 $ 20.22
Assumptions used in the estimation of fair value of options granted      
Weighted average expected volatility 34.00% 33.00% 31.00%
Expected dividend yield 0.00% 0.00% 0.00%
Period of settlement of publicly traded options 6 months    
Minimum      
Assumptions used in the estimation of fair value of options granted      
Risk-free interest rate 1.17% 1.51% 0.68%
Expected volatility 31.00% 28.00% 27.00%
Expected term (years) 5 years 7 days 5 years 7 days 5 years 10 days
Maximum      
Assumptions used in the estimation of fair value of options granted      
Risk-free interest rate 1.72% 1.90% 1.70%
Expected volatility 38.00% 37.00% 35.00%
Expected term (years) 5 years 15 days 5 years 22 days 5 years 6 months