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Employee Benefits - Weighted Average Assumptions Used in Determining Net Periodic Benefit Cost for Pension (Detail) - Pension Benefits
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]      
Discount rate 3.00% 4.10% 3.40%
Expected rate of return on plan assets 6.50% 6.80% 7.00%