Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Capital loss carryforwards	$ 547
Investment in subsidiary	441
Deferred tax assets, net operating loss carryforwards	238	$ 306
Deferred tax assets, accrued liabilities	125	35
Deferred tax assets, asset retirement obligations	94	123
Deferred tax assets, pension benefit obligations	43	39
Other	96	66
Total deferred tax assets before valuation allowance	1,584	569
Less: valuation allowance	(1,355)	(106)
Net deferred tax assets	229	463
Deferred tax liabilities, property and equipment	(213)	(800)
Deferred tax liabilities, other		(4)
Total deferred tax liabilities	(213)	(804)
Net deferred tax asset (liability)	$ 16
Net deferred tax asset (liability)		$ (341)