Acquisitions And Divestitures (Summary of Gain Computation) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Divestitures of property and equipment			$ 3,118	$ 107	$ 5,120
Asset retirement obligation assumed by purchasers			324	$ 89
Allocated goodwill			197
Gains on asset sales	$ 540	$ 1,400	$ 1,893		$ 1,072
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
Allocated oil and gas property basis sold		355
Allocated goodwill		197
Total assets sold		552
Gains on asset sales		$ 1,351