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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, 2020
Dec. 31, 2019
Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Dividend yield 4.00% 5.30% 2.90%
Expected volatility 43.00% 30.00% 22.00%
Risk-free interest rate 0.88% 2.30% 1.60%
Weighted-average fair value per share $ 5.38 $ 5.81 $ 9.01