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Share-Based Compensation Share-Based Compensation (Schedule of Stock Option Valuation Assumptions) (Details)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Schedule of Stock Option Valuation Assumptions [Abstract]    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate 6.50% 5.30%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate 19.40% 19.80%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term 3 years 3 months 14 days 2 years 11 months 2 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate 2.39% 1.49%