Other 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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			$ 9,132,925				$ 9,132,925
Current period change	$ 114,461			$ 91,173			383,446	$ 508,828
Balance	9,591,292			8,983,258			9,591,292	8,983,258
URA(D) On Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	600,922		304,425	247,741		$ (179,392)	304,425	(179,392)
Current period change	52,027			93,190			348,524	521,919
Balance	652,949	$ 600,922		340,978	$ 247,741		652,949	340,978
URA(D) On Securities OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Current period change				47				(1,549)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(231,955)		(201,717)	(227,527)		(215,747)	(201,717)	(215,747)
Current period change	60,628			(3,426)			30,390	(15,206)
Balance	(171,327)	(231,955)		(230,953)	(227,527)		(171,327)	(230,953)
Benefit Plan Net Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(71,830)		(74,556)	(65,116)		(67,418)	(74,556)	(67,418)
Current period change	1,806			1,363			4,532	3,665
Balance	(70,024)	(71,830)		(63,753)	(65,116)		(70,024)	(63,753)
Accumulated Other Comprehensive Income (Loss), Net of Deferred Income Taxes [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	297,137	(269,751)	28,152	(44,902)	(216,111)	(462,557)	28,152	(462,557)
Current period change	114,461	566,888	(297,903)	91,174	171,209	246,446
Balance	$ 411,598	$ 297,137	$ (269,751)	$ 46,272	$ (44,902)	$ (216,111)	$ 411,598	$ 46,272