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Stock-Based Compensation (Performance Share Awards Activity) (Details) - Performance shares - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Performance Shares      
Balance at beginning of period (in shares) 1,226,031    
Grants (in shares) 383,813    
Forfeitures (in shares) (43,768)    
Payouts (in shares) (438,639)    
Balance at end of period (in shares) 1,127,437 1,226,031  
Weighted Average Grant Date Fair Value      
Balance at beginning of period (in dollars per share) $ 107.35    
Grants (in dollars per share) 129.68 $ 115.85 $ 105.64
Forfeitures (in dollars per share) 116.94    
Payouts (in dollars per share) 99.22    
Balance at end of period (in dollars per share) $ 117.06 $ 107.35