Retirement Benefits Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Qualified Pension Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost			$ 13,444		$ 24,337
Defined Benefit Plan, Interest Cost			11,191		25,180
Qualified Pension Benefits [Member] | Parent Company [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	$ 6,733	$ 6,172	13,444	$ 12,169
Defined Benefit Plan, Interest Cost	5,613	6,292	11,191	12,590
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(12,039)	(12,449)	(24,120)	(24,951)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(476)	(292)	(952)	(787)
Defined Benefit Plan, Amortization of Gain (Loss)	3,072	2,099	5,901	4,080
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	2,903	1,822	5,464	3,101
Qualified Pension Benefits [Member] | Subsidiaries [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	6,733	6,172	13,444	12,169
Defined Benefit Plan, Interest Cost	5,613	6,292	11,191	12,590
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(12,040)	(12,451)	(24,121)	(24,955)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(378)	(393)	(756)	(787)
Defined Benefit Plan, Amortization of Gain (Loss)	5,620	4,866	10,931	9,522
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	5,548	4,486	10,689	8,539
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost			229		756
Defined Benefit Plan, Interest Cost			586		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	229	404
Defined Benefit Plan, Interest Cost	293	362	586	740
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	87	87	174	174
Defined Benefit Plan, Amortization of Gain (Loss)	588	512	1,175	1,098
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	1,083	1,137	2,164	2,416
Supplemental Employee Retirement Plan [Member] | Subsidiaries [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	115	176	229	404
Defined Benefit Plan, Interest Cost	293	362	586	740
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	87	87	174	174
Defined Benefit Plan, Amortization of Gain (Loss)	635	575	1,271	1,234
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	1,130	1,200	2,260	2,552
Other Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost			82		190
Defined Benefit Plan, Interest Cost			154		$ 368
Other Benefit [Member] | Parent Company [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	41	46	82	95
Defined Benefit Plan, Interest Cost	77	93	154	184
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(91)	(98)	(183)	(195)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	2	0	3	0
Defined Benefit Plan, Amortization of Gain (Loss)	(10)	(19)	(20)	(41)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	19	22	36	43
Other Benefit [Member] | Subsidiaries [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Service Cost	41	46	82	95
Defined Benefit Plan, Interest Cost	77	93	154	184
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(91)	(98)	(183)	(195)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	2	0	3	0
Defined Benefit Plan, Amortization of Gain (Loss)	(14)	(33)	(28)	(69)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ 15	$ 8	$ 28	$ 15