Acquisitions and Dispositions (Details) (USD $)	3 Months Ended			6 Months Ended			9 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011	Sep. 30, 2011	Dec. 31, 2011
Current Assets [Abstract]
Accounts Receivable, Net	$ 19,000,000			$ 19,000,000
Other Current Assets	11,000,000			11,000,000
Total Current Assets	30,000,000			30,000,000
Property, Plant, and Equipment, Net	294,000,000			294,000,000
Total Assets Held for Sale	324,000,000			324,000,000
Current Liabilities [Abstract]
Accounts Payable - Trade	9,000,000			9,000,000
Asset Retirement Obligations	89,000,000			89,000,000
Deferred Tax Liability	136,000,000			136,000,000
Total Liabilities Associated with Assets Held for Sale	234,000,000			234,000,000				0
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Oil and Gas Sales	65,000,000		112,000,000	140,000,000		225,000,000
Income before income taxes	39,000,000		69,000,000	79,000,000		137,000,000
Income tax expense	22,000,000		44,000,000	47,000,000		64,000,000
Discontinued Operations, Net of Tax	17,000,000		25,000,000	32,000,000		73,000,000
Marcellus Shale Joint Venture [Abstract]
Equity Method Investment, Ownership Percentage							50.00%
Undeveloped acres purchased							628,000
Business Acquisition, Cost of Acquired Entity, Purchase Price							1,300,000,000
Payments On Venture To Explore And Develop Oil And Gas Properties				610,000,000
Remaining annual installments to purchase joint venture partnership				2
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
Period over which Carried Cost Obligation is expected to extend				8 years
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%
Expected Divestiture Proceeds	127,000,000			127,000,000
Expected Income Tax Benefit	103,000,000			103,000,000
Pending Sale of Onshore US Properties [Abstract]
Onshore US Subsequent Asset Sales Proceeds	937,000,000			937,000,000
Onshore US Subsequent Asset Sales Net Book Value	765,000,000			765,000,000
Total Purchase Price [Abstract]
Unproved Oil and Gas Properties	853,000,000			853,000,000
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	$ 1,308,000,000	[1]		$ 1,308,000,000	[1]

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