Retirement Plans - Actuarial Assumptions Used for Pension Plans & Postretirement Medical Plan (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plans
Benefit Obligations:
Discount rate	2.90%	3.90%	3.30%
Rate of compensation increase	3.80%	3.80%	4.50%
Net Periodic Benefit Cost:
Discount rate, Service cost	3.90%	3.90%	3.70%
Discount rate, Interest cost	3.40%	3.30%	3.70%
Expected return on plan assets	7.10%	7.20%	7.30%
Rate of compensation increase	3.80%	4.50%	4.60%
Postretirement Medical Plan
Benefit Obligations:
Discount rate	2.80%	3.90%	3.20%
Initial health care trend rate	6.50%	6.90%	7.30%
Ultimate trend rate	4.50%	4.50%	4.50%
Year in which ultimate trend rate is reached	2038	2038	2038