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Assumptions Used To Determine Compensation Expense for Management Stock Purchase Program (Detail) - Management Stock Purchase Plan - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.50% 0.60% 0.60%
Risk-free interest rate 0.39% 0.16% 0.07%
Expected life in years 7 months 6 days 7 months 6 days 7 months 6 days
Expected volatility 18.00% 17.00% 20.00%
Fair value $ 83.23 $ 60.47 $ 51.82