Divestitures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Disposal Group, Including Discontinued Operation, Revenue	$ 10		$ 75
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(1)		39
Discontinued Operation, Tax Effect of Discontinued Operation	7		25
Operating Income (Loss), Net of Tax	(8)		14
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	37		0
Discontinued Operations, Net of Tax	29		14
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale Proceeds	76		0
Gain on Divestitures	(15)	[1]	0	[1]
North Sea Assets Sold [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale Proceeds	38
Interest in Cook Field - North Sea	13.00%
US Onshore Assets Sold [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale Proceeds	55
Net Book Value of Assets Sold	(28)
Goodwill Allocated to Assets Sold	(3)
Asset Retirement Obligations Associated with Assets Sold	5
Other Closing Adjustments	(14)	[2]
Gain on Divestitures	$ 15

[1] See Note 3. Divestitures

[2] Other closing adjustments also include adjustments related to onshore US property sales completed during 2012.