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Schedule of Valuation Assumptions for All Awards Issued (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate     1.10%
Dividend yield [1]     2.30%
Expected life in years 0 years 0 years 3 years 4 months 24 days
Expected volatility     24.00%
Performance Shares and Restricted Stock Units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield [2]   2.20%  
[1] The dividend yield assumption is used for both SOs and the RSUs granted in 2015.
[2] Dividend equivalent rights applied to LTI program starting 2017.