XML 76 R58.htm IDEA: XBRL DOCUMENT v3.8.0.1
Share-Based Compensation Plans - Estimated Fair Value of Share Awards (Details) - Stock option
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Average risk-free interest rate (as a percent) 2.00% 1.40% 1.60%
Expected dividend yield (as a percent) 2.00% 2.10% 1.50%
Expected volatility (as a percent) 31.00% 33.00% 32.00%
Expected term (years) 6 years 6 years 6 years