Weighted Average Assumptions Relate to All Pension Plans of Company, Except for Certain Multi-Employer and Defined Contribution Plans (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Discount rate	2.20%	2.90%
Rate of increase in future compensation levels	3.70%	3.80%
Assumed long-term rate of return on plan assets	6.20%	6.30%