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Equity-Based Compensation Plans Assumption Used in Monte Carlo Model to Estimate Fair Value of Performance Shares Awards (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value $ 61.95    
Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value $ 18.82 $ 14.42 $ 20.82
Risk free rate 2.05%    
Measurement period 6 years    
Volatility 30.00%    
Performance shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Closing price of stock on date of grant $ 56.75    
Risk free rate 1.42%    
Measurement period 3 years    
Volatility 35.00%