Retirement, Other Postretirement Benefits, And Defined Contribution Plans Actuarial Assumptions Used In Determining Net Periodic And Other Postretirement Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Non-Qualified Pension Plans [Member]
Defined Benefit Plan, Accumulated Benefit Obligation	$ 161,300	$ 143,400
Qualified Pension Plans [Member]
Defined Benefit Plan, Accumulated Benefit Obligation	$ 8,400,000	$ 7,800,000
Net Periodic Pension And Other Postretirement Benefit Costs [Member]
Weighted-average rate of increase in future compensation levels		3.98%	3.98%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.75%	4.75%	4.75%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Pre-65 Retirees [Member]
Assumed health care cost trend rate	6.13%	6.59%	6.95%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2027	2027	2027
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Post - 65 Retirees [Member]
Assumed health care cost trend rate	6.25%	7.15%	7.25%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2027	2026	2027
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Non-Qualified Pension Plans [Member] | Service Cost [Member]
Weighted-average discount rate	2.71%	3.94%	3.35%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Non-Qualified Pension Plans [Member] | Interest Cost [Member]
Weighted-average discount rate	2.25%	3.46%	2.76%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Qualified Pension Plans [Member] | Service Cost [Member]
Weighted-average discount rate	3.42%	4.57%	3.89%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Qualified Pension Plans [Member] | Interest Cost [Member]
Weighted-average discount rate	2.99%	4.15%	3.44%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Other Postretirement Benefits Plan [Member] | Service Cost [Member]
Weighted-average discount rate	3.27%	4.62%	3.88%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Other Postretirement Benefits Plan [Member] | Interest Cost [Member]
Weighted-average discount rate	2.41%	4.01%	3.33%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Minimum [Member]
Weighted-average rate of increase in future compensation levels	0.0398%
Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Maximum [Member]
Weighted-average rate of increase in future compensation levels	0.044%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member]
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.75%	4.75%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Pre-65 Retirees [Member]
Assumed health care cost trend rate	5.87%	6.13%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2030	2027
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Post - 65 Retirees [Member]
Assumed health care cost trend rate	6.31%	6.25%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2028	2027
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Non-Qualified Pension Plans [Member]
Weighted-average discount rate	1.61%	2.72%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Qualified Pension Plans [Member]
Blended weighted-average discount rate	0.00028%	0.00034%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Other Postretirement Benefits Plan [Member]
Weighted-average discount rate	2.62%	3.26%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Minimum [Member]
Weighted-average rate of increase in future compensation levels	0.0004%	0.00044%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Minimum [Member] | Qualified Pension Plans [Member]
Weighted-average discount rate	0.00026%	0.00033%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Maximum [Member]
Weighted-average rate of increase in future compensation levels	0.00044%	0.0004%
Pension Postretirement Benefit Obligations And Other Postretirement Accumulated Postretirement Benefit Obligations [Member] | Maximum [Member] | Qualified Pension Plans [Member]
Weighted-average discount rate	0.00028%	0.00034%
Pension Assets [Member] | Net Periodic Pension And Other Postretirement Benefit Costs [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	7.00%	7.25%	7.50%
Other Postretirement Non Taxable Assets [Member] | Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Minimum [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	0.0625%	0.00065%	0.065%
Other Postretirement Non Taxable Assets [Member] | Net Periodic Pension And Other Postretirement Benefit Costs [Member] | Maximum [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	0.07%	0.0725%	0.075%
Taxable [Member] | Net Periodic Pension And Other Postretirement Benefit Costs [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	5.25%	5.50%	5.50%