Retirement and Employee Benefit Plans (Schedule of Assumptions Used - Benefit Obligations) (Details)	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.50%	3.50%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.10%	3.70%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.80%	3.50%