Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Flows From Operating Activities [Abstract]
Net Income	$ 1,027	$ 453	$ 725
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities [Abstract]
Depreciation, Depletion and Amortization	1,403	965	883
Asset Impairments	104	759	144
Dry Hole Cost	182	105	58
Deferred Income Taxes	109	(81)	71
Dividends (Income) from Equity Method Investees, Net	7	30	21
Unrealized (Gain) Loss on Commodity Derivative Instruments	(109)	22	(70)
Gain on Divestitures	(72)	(25)	(113)
Stock Based Compensation	65	58	54
Other Adjustments for Noncash Items Included in Income	83	40	15
Changes in Operating Assets and Liabilities [Abstract]
(Increase) in Accounts Receivable	(130)	(249)	(86)
(Increase) Decrease in Other Current Assets	(45)	7	18
Increase in Accounts Payable	237	3	234
Increase in Current Income Taxes Payable	64	37	31
Increase in Other Current Liabilities	18	38	3
Other Operating Assets and Liabilities, Net	(10)	8	(42)
Net Cash Provided by Operating Activities	2,933	2,170	1,946
Cash Flows from Investing Activities [Abstract]
Additions to Property, Plant and Equipment	(3,650)	(2,594)	(1,885)
Marcellus Shale Asset Acquisition	0	(527)	0
DJ Basin Asset Acquisition	0	0	(458)
Additions to Equity Method Investments	(41)	(69)	0
Proceeds from Divestitures	1,160	77	564
Other	4	0	0
Net Cash Used in Investing Activities	(2,527)	(3,113)	(1,779)
Cash Flows from Financing Activities [Abstract]
Exercise of Stock Options	56	38	47
Excess Tax Benefits from Stock-Based Awards	25	15	25
Dividends Paid, Common Stock	(164)	(143)	(127)
Purchase of Treasury Stock	(13)	(17)	(13)
Proceeds from Credit Facilities	150	520	760
Repayment of Credit Facilities	(150)	(870)	(792)
Repayment of CONSOL Installment Loan	(328)	0	0
Proceeds from Issuance of Senior Long-Term Debt, Net	0	1,828	0
Settlement of Interest Rate Derivative Instrument	0	(40)	0
Repayment of Capital Lease Obligation	(45)	(3)	0
Other	(5)	(11)	0
Net Cash Provided By (Used in) Financing Activities	(474)	1,317	(100)
Increase (Decrease) in Cash and Cash Equivalents	(68)	374	67
Cash and Cash Equivalents at Beginning of Period	1,455	1,081	1,014
Cash and Cash Equivalents at End of Period	$ 1,387	$ 1,455	$ 1,081