Retirement and Employee Benefit Plans (Schedule of Assumptions Used - Net Periodic Benefit Cost) (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.50%	3.50%	3.50%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.70%	3.70%	4.35%
Expected return on plan assets	6.50%	7.00%	7.00%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.50%	4.35%	4.35%