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Share-Based Compensation (Valuation Assumptions) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Options [Member] | Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate   1.80% 1.60%
Dividend yield   5.20% 5.20%
Historical volatility factor   24.00% 23.60%
Weighted-average expected life   7 years 6 years
First Portion [Member] | 2016 Grant [Member] | 2008 plan [Member] | Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 1.01%    
Historical volatility factor 19.00%    
First Portion [Member] | 2015 Grant [Member] | 2008 plan [Member] | Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate   0.99%  
Historical volatility factor   17.00%  
First Portion [Member] | 2014 Grant [Member] | 2008 plan [Member] | Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate     0.68%
Historical volatility factor     24.00%