Acquisitions And Divestitures (Summary of Gain Computation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Business Acquisition [Line Items]
Divestitures of property and equipment	$ 1,680	$ 27	$ 1,889	$ 35
Asset retirement obligation assumed by purchasers			310	$ 48
Gains on asset sales	1,351		1,351
Oil and Gas Properties [Member]
Business Acquisition [Line Items]
Divestitures of property and equipment	1,653
Asset retirement obligation assumed by purchasers	250
Total consideration received	1,903		1,903
Allocated oil and gas property basis sold	355		355
Allocated goodwill	197
Total assets sold	552		$ 552
Gains on asset sales	$ 1,351