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Stock-based Compensation Plans - Weighted-Average Assumptions (Detail) - Employee Stock Option - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Dividend yield 2.60% 2.30% 2.70%
Expected volatility 26.00% 27.00% 30.00%
Risk-free interest rate 2.60% 2.40% 1.70%
Expected option life in years 7 years 7 years 7 years
Weighted-average fair value per share $ 17.37 $ 20.85 $ 17.45