Acquisitions And Divestitures (Summary of Divestiture Activity) (Details) $ in Millions		3 Months Ended		12 Months Ended
		Sep. 30, 2016 USD ($) MMBoe	Jun. 30, 2016 USD ($) MMBoe	Dec. 31, 2017 USD ($) MMBoe	Dec. 31, 2016 USD ($) MMBoe		Dec. 31, 2015 USD ($) MMBoe
Business Acquisition [Line Items]
Proceeds Received				$ 417	$ 3,113	[1]	$ 107	[1]
Gains on Sale				$ 217	$ 1,483	[1]	$ (7)	[1]
Proved Reserves (MMBoe) | MMBoe	[2]			6	157		7
US [Member]
Business Acquisition [Line Items]
Proved Reserves (MMBoe) | MMBoe	[2]			6	157		7
Non Core Assets [Member]
Business Acquisition [Line Items]
Proceeds Received				$ 415
Gains on Sale				$ 212
Non Core Assets [Member] | US [Member]
Business Acquisition [Line Items]
Proceeds Received		$ 1,653	$ 200		$ 1,853
Gains on Sale		$ 726	$ 83		$ 809
Proved Reserves (MMBoe) | MMBoe		146	11		157
Percentage of U.S. Proved Reserves		9.00%	1.00%		10.00%

[1] Prior year amounts have been recast due to change in accounting principle. See Note 2 in “Item 8. Financial Statements and Supplementary Data” of this report.

[2] Gas reserves are converted to Boe at the rate of six Mcf per Bbl of oil, based upon the approximate relative energy content of gas and oil. This rate is not necessarily indicative of the relationship of natural gas and oil prices. Bitumen and NGL reserves are converted to Boe on a one-to-one basis with oil.