Revisions To Financial Statements (Schedule Of Prior Period Financial Statements - Stockholder's Equity) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Balance		$ 9,132,925			$ 9,132,925
Net income (loss)	$ 190,880		$ 332,868		207,492	$ 687,419
Balance	9,286,299		8,836,817		9,286,299	8,836,817
Retained Earnings [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Balance	10,255,692	10,306,571	9,828,847	$ 9,531,433	10,306,571	9,531,433
Net income (loss)	190,880	16,612	332,868	354,551
Balance	$ 10,384,645	$ 10,255,692	10,104,716	9,828,847	$ 10,384,645	10,104,716
As Previously Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Net income (loss)			342,855			691,755
Balance			8,884,160			8,884,160
As Previously Reported [Member] | Retained Earnings [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Balance			9,866,203	9,574,440		9,574,440
Net income (loss)			342,855	348,900
Balance			10,152,059	9,866,203		10,152,059
Impact of Revisions [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Net income (loss)			(9,987)			(4,336)
Balance			(47,343)			(47,343)
Impact of Revisions [Member] | Retained Earnings [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Balance			(37,356)	(43,007)		(43,007)
Net income (loss)			(9,987)	5,651
Balance			$ (47,343)	$ (37,356)		$ (47,343)