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Share-Based Compensation Plans Time-based Vesting Option Activity Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend payment (dollars per share) $ 0.55 $ 0.40 $ 0.40
Time Based Vesting Option      
Weighted-average assumptions used to estimate fair value:      
Expected dividend yield 0.70%    
Expected stock price volatility 28.90%    
Risk-free interest rate 1.70%    
Contractual term in years 4 years 6 months    
Market price (in dollars per share) $ 78.70    
Weighted-average fair value estimate at grant date $ 0.1    
Weighted-average fair value estimate per share (in dollars per share) $ 21.09    
Performance-based Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend payment (dollars per share) $ 0.40    
Performance period for achieving stock price hurdles 3 years    
Weighted-average assumptions used to estimate fair value:      
Expected dividend yield 0.80% 1.30%  
Expected stock price volatility 29.30% 30.90%  
Risk-free interest rate 1.80% 1.10%  
Contractual term in years 4 years 6 months 4 years 6 months  
Market price (in dollars per share) $ 78.70    
Weighted-average fair value estimate at grant date $ 3.6 $ 3.5  
Weighted-average fair value estimate per share (in dollars per share) $ 11.97 $ 6.01