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Stock-Based Compensation Plans (Details 5) - Performance awards - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]      
Dividend yield (as a percent) 3.20% 3.30% 3.00%
Estimated volatility, minimum (as a percent) 15.30% 15.20% 12.00%
Estimated volatility, maximum (as a percent) 19.70% 22.80% 17.30%
Risk-free interest rate, minimum (as a percent) 0.69% 0.44% 0.07%
Risk-free interest rate, maximum (as a percent) 1.61% 0.88% 1.09%
Estimated performance award value based on total shareholder return measure (in dollars per share) $ 175.86 $ 131.24 $ 139.18
Historical volatility (as a percent) 50.00% 50.00% 50.00%
Implied volatility (as a percent) 50.00% 50.00% 50.00%
Market closing price (in dollars per share) $ 179.07 $ 161.66 $ 166.23