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Share-Based Compensation - Stock Options, Schedule of Assumptions for Fair Value of Options Granted (Details) - Stock Options
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 2.00% 2.00% 1.90%
Weighted average expected life in years 5 years 10 months 5 years 10 months 5 years 10 months
Expected volatility 25.10% 26.00% 27.20%
Dividend yield 1.90% 2.00% 2.20%