Comprehensive Income (Loss) (Components Of Accumulated Other Comprehensive Income (Loss), Net Of Tax, In The Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 6,414,313				$ 6,414,313
Net increase (decrease) during the period	$ (60,621)			$ 52,187			(98,804)	$ 131,171
Ending balance	6,757,778			6,155,666			6,757,778	6,155,666
URA(D) On Securities [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance	254,645		313,161	222,068		$ 124,612	313,161	124,612
Net increase (decrease) during the period	(41,322)			35,967			(99,838)	133,422
Ending balance	213,323	$ 254,645		258,034	$ 222,068		213,323	258,034
Foreign Currency Translation Adjustments [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance	44,974		28,727	(6,931)		14,267	28,727	14,267
Net increase (decrease) during the period	(20,862)			14,414			(4,615)	(6,783)
Ending balance	24,112	44,974		7,483	(6,931)		24,112	7,483
Benefit Plan Net Gain (Loss) [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance	(69,784)		(73,870)	(71,829)		(74,556)	(73,870)	(74,556)
Net increase (decrease) during the period	1,562			1,806			5,649	4,532
Ending balance	(68,221)	(69,784)		(70,023)	(71,829)		(68,221)	(70,023)
Accumulated Other Comprehensive Income (Loss), Net Of Deferred Income Taxes [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance	229,835	163,955	268,018	143,308	(114,027)	64,324	268,018	64,324
Net increase (decrease) during the period	(60,621)	65,880	(104,063)	52,187	257,335	(178,351)
Ending balance	$ 169,214	$ 229,835	$ 163,955	$ 195,495	$ 143,308	$ (114,027)	$ 169,214	$ 195,495