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Stock-Based Compensation - Options (Details) (Stock Options [Member], USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Stock Options [Member]
        
Number of shares        
Beginning Balance (in shares)     2.8  
Granted (in shares)     0.2  
Forfeited (in shares)     0  
Exercised (in shares)     (0.2)  
Ending balance (in shares) 2.8   2.8  
Options exercisable (in shares) 2.3   2.3  
Weighted average grant date fair value        
Beginning balance (dollars per share)     $ 21.73  
Granted (dollars per share)     $ 51.91  
Forfeited (dollars per share)     $ 50.67  
Exercised (dollars per share)     $ 20.18  
Ending balance (dollars per share) $ 24.07   $ 24.07  
Options exercisable (dollars per share) $ 19.18   $ 19.18  
Ending balance weighted average remaining contractual term (in years)     5 years 4 months 13 days  
Options exercisable weighted average remaining contractual term (in years)     4 years 7 months 10 days  
Ending balance aggregate intrinsic value $ 88.1   $ 88.1  
Options exercisable aggregate intrinsic value 86.1   86.1  
Total intrinsic value of options exercised $ 0.4 $ 1.1 $ 6.5 $ 13.4