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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, 2019
Dec. 31, 2018
Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Dividend yield 5.30% 2.90% 2.70%
Expected volatility 30.00% 22.00% 19.00%
Risk-free interest rate 2.30% 1.60% 1.00%
Weighted-average fair value per share $ 5.81 $ 9.01 $ 9.46