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Shareholders' Equity (Details) - Class A Common Stock [Member] - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2016
Jun. 04, 2015
Class of Stock [Line Items]      
Stock repurchased, shares 0.5 2.0  
Stock repurchased, value $ 52.3 $ 202.4  
Weighted average price per share $ 108.63 $ 100.61  
New Stock Repurchase Program [Member]      
Class of Stock [Line Items]      
Stock repurchase program, authorized     $ 1,000.0