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Equity - Share Repurchase Plan, Preferred Stock (Details)
$ / shares in Units, $ in Millions
 12 Months Ended
Oct. 23, 2018
shares
Dec. 31, 2020
USD ($)
item
$ / shares
shares
Dec. 31, 2019
USD ($)
item
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Share Repurchase Plan        
Increase in authorized number of shares to be repurchased 5,000,000.0      
Repurchase of common shares (in shares)   3,700,000 600,000 6,100,000
Average costs per share | $ / shares   $ 91.80 $ 84.33 $ 79.94
Value of shares repurchased | $   $ 337.3 $ 50.0 $ 484.9
Remaining number of common stock authorized for repurchase under stock repurchase program (in shares)   2,800,000    
Percent of outstanding stock authorized for repurchase   4.00%    
Preferred Stock        
Preferred stock, authorized shares   5,000,000 5,000,000  
Preferred stock, par value (in dollars per share) | $ / shares   $ 0.001 $ 0.001  
Preferred stock, issued shares   0 0  
Preferred stock, outstanding shares   0 0  
Minimum number of series in which preferred shares may be issued | item   1 1