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Share-Based Payments - Weighted-average Assumptions (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock Options [Member]      
Schedule of Weighted Average Assumptions Used to Determine Fair Value of Stock Options      
Expected volatility (percent) 30.50% 37.20% 39.50%
Risk-free interest rate (percent) 2.10% 1.60% 1.90%
Expected life (years) 7 years 8 months 7 years 6 months 7 years 8 months 12 days
Dividend yield (percent) 2.20% 2.10% 2.10%
Stock Appreciation Rights (SARs) [Member]      
Schedule of Weighted Average Assumptions Used to Determine Fair Value of Stock Options      
Expected volatility (percent) 28.70% 25.90%  
Risk-free interest rate (percent) 1.90% 1.90%  
Expected life (years) 2 years 1 month 5 years 3 months  
Dividend yield (percent) 0.00% 0.00%