Acquisitions and Dispositions (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012 acre		Sep. 30, 2011	Sep. 30, 2012 acre		Sep. 30, 2011
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Oil and Gas Sales	$ 54,000,000		$ 45,000,000	$ 194,000,000		$ 271,000,000
Income before income taxes	38,000,000		23,000,000	117,000,000		161,000,000
Income tax expense	3,000,000		73,000,000	50,000,000		139,000,000
Operating Income (Loss), Net of Tax	35,000,000		(50,000,000)	67,000,000		22,000,000
Gain on Sale, Net of Tax	22,000,000		0	22,000,000		0
Discontinued Operations, Net of Tax	57,000,000		(50,000,000)	89,000,000		22,000,000
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash Proceeds				(1,161,000,000)		(77,000,000)
Gain on Asset Sale	157,000,000	[1]	0	167,000,000	[1]	26,000,000	[1]
Marcellus Shale Joint Venture [Abstract]
Equity Method Investment, Ownership Percentage			50.00%			50.00%
Undeveloped Acres Purchased (acres)	628,000			628,000
Payments to Acquire Interest in Joint Venture				938,000,000
Ratio of funding on share of future drilling and completion costs	one-third			one-third
Maximum amount to be paid each calendar year for funding of future drilling and completion costs				400,000,000
Funding of joint venture's future drilling and completion costs				2,100,000,000
Natural gas price agreed upon benchmark, average (per MMBtu)				4.00
Payable with imputed interest, discount	17,000,000			17,000,000
North Sea Divestiture [Abstract]
Interest in Dumbarton and Lochranza Fields	30.00%			30.00%
Total Purchase Price [Abstract]
Unproved Oil and Gas Properties	803,000,000			803,000,000
Proved Oil and Gas Properties	386,000,000			386,000,000
Investment in CONE Gathering LLC	69,000,000			69,000,000
Total Assets Acquired	1,258,000,000	[2]		1,258,000,000	[2]
North Sea Assets Sold [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash Proceeds				117,000,000
Net Book Value of Assets Sold				(256,000,000)
Goodwill Allocated to Assets Sold				0
Asset Retirement Obligation Associated with Assets Sold				55,000,000
Income Tax Benefit Recognized				106,000,000
Other Closing Adjustments				0
US Onshore Assets Sold [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash Proceeds				1,044,000,000
Net Book Value of Assets Sold				(838,000,000)
Goodwill Allocated to Assets Sold				(61,000,000)
Asset Retirement Obligation Associated with Assets Sold				20,000,000
Income Tax Benefit Recognized				0
Other Closing Adjustments				2,000,000
Gain on Asset Sale				$ 167,000,000

[1] See Note 3. Acquisitions and Divestitures.

[2] Total reflects impact of $17 million imputed interest on CONSOL installment payments.