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Share-Based Payments (Summary of Stock Option and Performance Share Unit Pricing Assumptions) (Details)
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sign-on Grant Performance Share Unit Plans [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate 2.70%  
Expected dividend yield 1.53%  
Expected lives 1 year  
Expected volatility 29.20%  
Stock Options [Member] | Stock Option Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate 2.70% 2.00%
Expected dividend yield 2.11% 2.14%
Expected lives 5 years 5 years
Expected volatility 28.10% 27.80%
Performance Share Units [Member] | Senior Executive and Employee Performance Share Unit Plans [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate 1.90%  
Expected dividend yield 2.09%  
Expected lives 3 years  
Expected volatility 31.10%  
Average expected volatility of comparable companies 34.10%