Property Transactions - Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations, Net of Tax	$ 0	$ 71		$ 62
North Sea Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and Gas Sales		37		208
Income Before Income Taxes		12	[1]	101	[1]
Income Tax Expense		6		55
Operating Income, Net of Tax		6		46
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax		$ 65		$ 16

[1] Income before income taxes for 2012 includes exploration expense of $27 million related to the Selkirk field which was determined uneconomic for joint development.