Employee Benefits - Weighted Average Assumptions Used In Determining Benefit Obligations (Detail)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.60%	3.30%	4.40%	3.70%
Pension
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.60%	3.30%
Rate of compensation increases	3.00%	3.00%
Health Care and Life
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.50%	3.20%