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Stock-Based Compensation Programs - Weighted average assumptions (Details) - Stock option and SSARs
1 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Weighted average assumptions used in estimation of fair values of options    
Expected dividend yield (as a percent) 1.03% 0.68%
Expected stock price volatility (as a percent) 21.98% 20.49%
Risk-free interest rate (as a percent) 2.47% 2.07%
Expected life of options 6 years 1 month 6 days 5 years 11 months 9 days