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Employee Benefits - Assumptions Used to Estimate Fair Value of SARs Using Black-Scholes Option Valuation Model (Detail) - Cash-Settled Stock Appreciation Rights - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted average fair value per SAR (dollars per share) $ 29.02 $ 37.63
Weighted-average volatility 22.08% 21.24%
Weighted-average risk-free interest rate 1.29% 0.81%
Dividend yield 0.00% 0.00%