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Share-Based Payments (Summary of Stock Option and Performance Share Unit Pricing Assumptions) (Details)
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Sign-on Grant Performance Share Unit Plans [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate 1.70% 1.00%
Expected dividend yield 2.37% 2.69%
Expected volatility 28.60% 27.90%
Stock Options [Member] | Stock Option Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate 2.10% 1.20%
Expected dividend yield 2.05% 2.68%
Expected lives 5 years 5 years
Expected volatility 27.90% 26.50%
Performance Share Units, Liability Classified Awards [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 1.40% 1.20%
Expected dividend yield 1.92% 2.49%
Expected lives 3 years 3 years
Expected volatility 28.20% 29.90%
Average expected volatility of comparable companies 37.00% 37.00%