Share-Based Compensation Share-Based Compensation (Schedule of Stock Option Valuation Assumptions) (Details) |
12 Months Ended | ||
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Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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Schedule of Stock Option Valuation Assumptions [Abstract] | |||
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate | 5.30% | 6.20% | 4.70% |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate | 19.80% | 19.10% | 17.80% |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term | 2 years 11 months 2 days | 2 years 11 months 4 days | 2 years 9 months 25 days |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate | 1.49% | 0.91% | 0.98% |