Retirement Benefits Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Qualified Pension Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost			$ 20,166		$ 24,337
Defined Benefit Plan, Interest Cost			16,786		25,180
Qualified Pension Benefits [Member] | Parent Company [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	$ 6,722	$ 6,084	20,166	$ 18,253
Defined Benefit Plan, Interest Cost	5,595	6,295	16,786	18,885
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(12,060)	(12,476)	(36,179)	(37,427)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(476)	(393)	(1,428)	(1,180)
Defined Benefit Plan, Amortization of Gain (Loss)	2,951	2,040	8,852	6,120
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	2,732	1,550	8,197	4,651
Qualified Pension Benefits [Member] | Subsidiaries [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	6,722	6,084	20,166	18,253
Defined Benefit Plan, Interest Cost	5,595	6,295	16,786	18,885
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(12,061)	(12,478)	(36,182)	(37,433)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(378)	(393)	(1,135)	(1,180)
Defined Benefit Plan, Amortization of Gain (Loss)	5,465	4,761	16,396	14,283
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	5,343	4,269	16,031	12,808
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost			344		756
Defined Benefit Plan, Interest Cost			879		1,464
Supplemental Employee Retirement Plan [Member] | Parent Company [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	115	176	344	580
Defined Benefit Plan, Interest Cost	293	362	879	1,102
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	87	87	262	262
Defined Benefit Plan, Amortization of Gain (Loss)	588	512	1,763	1,610
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	1,083	1,137	3,248	3,554
Supplemental Employee Retirement Plan [Member] | Subsidiaries [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	115	176	344	580
Defined Benefit Plan, Interest Cost	293	362	879	1,102
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	87	87	262	262
Defined Benefit Plan, Amortization of Gain (Loss)	635	575	1,906	1,810
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	1,130	1,200	3,391	3,754
Other Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost			117		190
Defined Benefit Plan, Interest Cost			226		$ 368
Other Benefit [Member] | Parent Company [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	34	47	117	142
Defined Benefit Plan, Interest Cost	72	92	226	276
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(84)	(97)	(266)	(292)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	2	0	5	0
Defined Benefit Plan, Amortization of Gain (Loss)	(10)	(20)	(30)	(61)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	14	22	52	65
Other Benefit [Member] | Subsidiaries [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	34	47	117	142
Defined Benefit Plan, Interest Cost	72	92	226	276
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(84)	(97)	(266)	(292)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	2	0	5	0
Defined Benefit Plan, Amortization of Gain (Loss)	(11)	(34)	(40)	(103)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ 13	$ 8	$ 42	$ 23