Supplemental Oil And Gas Disclosures (Cost Incurred In Oil And Gas Property Acquisition, Exploration, And Development Activities Disclosure) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) $ / ft³	Dec. 31, 2015 USD ($) $ / ft³	Dec. 31, 2014 USD ($) $ / ft³
Supplemental Oil And Gas Disclosures [Abstract]
Proved property acquisition costs		$ 81	$ 1,455
Unproved property acquisition costs	$ 171	692	3,934
Exploration costs	17	50	232
Development costs	433	1,417	1,600
Capitalized costs incurred	$ 621	$ 2,240	$ 7,221
Full cost pool amortization per Mcfe | $ / ft³	0.38	1.00	1.10