Divestitures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Oil and Gas Sales	$ 12	$ 65		$ 21		$ 140
Income Before Income Taxes	5	39		4		79
Income Tax Expense	3	22		10		47
Operating Income (Loss), Net of Tax	2	17		(6)		32
Gain on Sale, Net of Tax	17	0		55		0
Discontinued Operations, Net of Tax	19	17		49		32
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Proceeds				114		10
Gain on Divestitures	0	(9)	[1]	(12)	[1]	(9)	[1]
North Sea Assets Sold [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Proceeds				54
US Onshore Assets Sold [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Proceeds				60
Net Book Value of Assets Sold				(53)
Goodwill Allocated to Assets Sold				(4)
Asset Retirement Obligations Associated with Assets Sold				5
Other Closing Adjustments				4
Gain on Divestitures				$ 12

[1] See Note 3. Divestitures