Pension and Other Postretirement Benefits - Schedule of Weighted Average Assumptions Used to Determine Benefit Obligations and Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.41%	3.12%
Rate of compensation increase	1.77%	3.25%
Discount rate	3.02%	3.89%	3.59%
Expected long-term rate of return on plan assets	6.28%	6.59%	6.89%
Rate of compensation increase	3.25%	3.26%	3.28%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.41%	3.12%
Discount rate	2.84%	3.94%	3.18%