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Stock-based Compensation Plans - Discounted Stock Purchase Plan Assumptions and Resulting Weighted Average Fair Value (Detail) - DSPP - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Dividend yield 2.30% 1.60% 1.70%
Expected volatility 27.00% 19.00% 24.00%
Risk free interest rate 0.20% 0.10% 0.10%
Weighted-average fair value per share $ 12.45 $ 12.67 $ 9.91