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Share-Based Compensation (Restricted Share Units and Stock Option Fair Value) (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option fair value (in dollars per share) $ 7.01 $ 5.78 $ 5.89
Stock Option Valuation Assumptions:      
Dividend yield 1.70% 1.80% 1.70%
Expected volatility 20.10% 23.00% 23.00%
Risk-free interest rate 2.20% 1.50% 1.60%
Expected option life (in years) 6 years 1 month 6 years 1 month 6 years
Restricted share units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average fair value of RSUs (in dollars per share) $ 37.77 $ 30.02 $ 29.41