Retirement, Other Postretirement Benefits, And Defined Contribution Plans Investments Held For Qualified Pension And Other Postretirement Plans Measured At Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Accumulated Benefit Obligation	$ 8,400,000	$ 7,800,000
Cash	2,316	1,407
Other pending transactions	(29,121)	(22,549)
Less: Other postretirement assets included in total investments	(76,033)	(66,572)
Defined Benefit Plan, Plan Assets, Amount	6,854,426	6,271,160
Qualified Pension Plans [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	6,957,264	6,358,874
Qualified Pension Plans [Member] | Preferred [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	15,756	10,379
Qualified Pension Plans [Member] | Common Stock [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,031,213	857,159
Qualified Pension Plans [Member] | Common Collective Trusts [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	2,958,767	2,698,697
Qualified Pension Plans [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	731,319	805,671
Qualified Pension Plans [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,029,370	762,577
Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	132,389
Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,128,107	1,008,371
Qualified Pension Plans [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	56,479	43,179
Qualified Pension Plans [Member] | Insurance Company General Account (Unallocated Contracts) [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	6,253	40,452
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other pending transactions	(21,931)	1,645
Plus: Other postretirement assets included in the investments of the qualified pension trust	76,033	66,572
Defined Benefit Plan, Plan Assets, Amount	737,866	686,262	$ 609,782
Other Postretirement Benefits Plan [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	683,764	618,045
Other Postretirement Benefits Plan [Member] | Common Collective Trusts [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	315,191	289,398
Other Postretirement Benefits Plan [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	144,102	139,227
Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	147,287	130,333
Other Postretirement Benefits Plan [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	16,965	1,877
Other Postretirement Benefits Plan [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	60,219	57,210
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,128,925	1,053,842
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Preferred [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	15,756	10,379
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Common Stock [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,031,213	857,159
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Common Collective Trusts [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	132,389
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	81,800	53,842
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	156	73
Fair Value Inputs Level 1 [Member] | Qualified Pension Plans [Member] | Insurance Company General Account (Unallocated Contracts) [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefits Plan [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	63,463	51,807
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefits Plan [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	46,498	49,930
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefits Plan [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	16,965	1,877
Fair Value Inputs Level 1 [Member] | Other Postretirement Benefits Plan [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,826,341	1,654,709
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Preferred [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Common Stock [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Common Collective Trusts [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	731,319	805,671
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,029,370	762,577
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	3,076	2,903
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	56,323	43,106
Fair Value Inputs Level 2 [Member] | Qualified Pension Plans [Member] | Insurance Company General Account (Unallocated Contracts) [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	6,253	40,452
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefits Plan [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	305,110	276,840
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefits Plan [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	97,604	89,297
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	147,287	130,333
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefits Plan [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 2 [Member] | Other Postretirement Benefits Plan [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	60,219	57,210
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Preferred [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Common Stock [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Common Collective Trusts [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Qualified Pension Plans [Member] | Insurance Company General Account (Unallocated Contracts) [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefits Plan [Member] | Defined Benefit Plan Total Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefits Plan [Member] | U.S. Government securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefits Plan [Member] | Registered Investment Companies [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	0	0
Fair Value Inputs Level 3 [Member] | Other Postretirement Benefits Plan [Member] | Other [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 0	$ 0