Supplemental Oil And Gas Disclosures (Results Of Operations For Oil And Gas Producing Activities Disclosure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Sales	$ 1,413	$ 2,074	$ 2,862
Production (lifting) costs	(839)	(989)	(776)
Depreciation, depletion and amortization	(371)	(1,028)	(884)
Impairment of natural gas and oil properties	(2,321)	(6,950)
Results of operations - income before income taxes	(2,118)	(6,893)	1,202
Provision (benefit) for income taxes		(2,619)	457
Results of operations	(2,118)	$ (4,274)	$ 745
Prior to Recognition of Valuation Allowance [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Provision (benefit) for income taxes	$ 805