Income Taxes (Schedule Of Deferred Tax Assets And Deferred Tax Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Line Items]
Net operating loss carryforward	$ 996	$ 882
Credit carryforwards	101	111
Deferred interest carryforward	43	0
Asset retirement obligations	41	40
Incentive plans	40	48
Net deferred hedge losses	0	11
South Texas Divestiture	75	0
Lease deferred tax assets	191	0
Other	47	51
Total deferred tax assets	1,534	1,143
Oil and gas properties, principally due to differences in basis, depletion and the deduction of intangible drilling costs for tax purposes	(2,628)	(2,248)
Other property and equipment, principally due to the deduction of bonus depreciation for tax purposes	(189)	(47)
Net deferred hedge gains	(4)	0
South Texas Divestiture	(35)	0
Lease deferred tax liabilities	(61)	0
Other	(6)	0
Deferred tax liabilities	(2,923)	(2,295)
Net deferred tax liability	(1,389)	(1,152)
Unrecognized tax benefits	39	$ 141	$ 124	$ 112
U.S. Federal Tax Credit Carryforward [Member] | U.S.
Valuation Allowance [Line Items]
Credit carryforwards	12
Research Tax Credit Carryforward [Member] | U.S.
Valuation Allowance [Line Items]
Credit carryforwards	88
Research Tax Credit Carryforward [Member] | Texas
Valuation Allowance [Line Items]
Credit carryforwards	1
Domestic Tax Authority [Member]
Valuation Allowance [Line Items]
Net operating loss carryforward	5,000
COLORADO
Valuation Allowance [Line Items]
Net operating loss carryforward	$ 177