Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.16%	3.69%
Rate of increase in future compensation levels	4.50%	4.50%
Discount rate	3.69%	4.38%	3.76%
Rate of increase in future compensation levels	4.50%	4.50%	4.50%
Expected long-term rate of return on assets	6.75%	6.75%	6.75%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.48%	3.29%
Discount rate	3.29%	4.15%	3.47%