Retirement Plans (Weighted-Average Actuarial Assumptions Used To Determine Benefit Obligations) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit obligations	3.26%	4.23%
Compensation increase - benefit obligations	4.10%	4.19%
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit obligations	3.13%	4.17%
Health care cost trend rate (employees under 65) - benefit obligations	5.64%	5.87%
Ultimate health care cost trend rate - benefit obligations	4.50%	4.50%
Year ultimate trend reached - benefit obligations	2038	2038