Acquisitions (Details) (USD $)	3 Months Ended								9 Months Ended	12 Months Ended				3 Months Ended	9 Months Ended	12 Months Ended			3 Months Ended		12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Sep. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Jun. 30, 2010 Dominion Acquisition Member	Sep. 30, 2010 Dominion Acquisition Member	Dec. 31, 2010 Dominion Acquisition Member	Apr. 30, 2010 Dominion Acquisition Member Tcfe A	Apr. 30, 2010 Dominion Acquisition Member Marcellus Shale A	Jun. 30, 2010 Cnx Gas Stock Acquisition [Member]	Jun. 30, 2010 Yukon Pocahontas Coal Company [Member]	Dec. 31, 2009 nisource [Member] A
Business Acquisition [Line Items]
Total Revenue and Other Income										$ 6,117,242,000	$ 5,236,021,000	$ 4,621,875,000				$ 133,850
Payments to Acquire Businesses, Net of Cash Acquired										0	3,470,212,000	0							966,811,000	30,000,000	8,275,000
Effective date of acquisition														April 30, 2010
Business Acquisition, Cost of Acquired Entity, Purchase Price																	3,470,212,000
Proved undeveloped reserves (Volume)	1,344,222,000				1,800,325,000					1,344,222,000	1,800,325,000	871,134,000	638,756,000				1
Gas and Oil Acreage, Unproved, Net	4,040,598,000									4,040,598,000							1,460,000				20,000
Gas and Oil Acreage, Undeveloped, Net	124,276,000									124,276,000								500,000
CNX Gas Acquisition Price Per Share																			$ 38.25
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage																			83.30%
Common Stock, Shares, Outstanding	227,056,000				226,162,000					227,056,000	226,162,000	181,086,000	180,550,000						151,000,000
Employee Service Share-based Compensation, Cash Flow Effect, Cash Used to Settle Awards																			24,223,000
Acquisition and Financing Fees										14,907,000	65,363,000	0			65,363,000
Payments to Acquire Royalty Interests in Mining Properties																				20,000,000
Basic Earnings Per Share, Pro Forma									$ 1.60
Net Income Attributable to CONSOL Energy Inc Shareholders	195,635,000	167,329,000	77,384,000	192,149,000	104,461,000	75,383,000	66,668,000	100,269,000		632,497,000	346,781,000	539,717,000				(5,364)
Business Acquisition, Pro Forma Information [Abstract]
Senior unsecured notes																	2,750,000,000
Shares of common stock issued in connection with acquisition transaction														44,275,000
Business Acquisition, Pro Forma Revenue															5,303,008,000
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax									465,740,000						414,205,000
Business Acquisition, Pro Forma Net Income (Loss)															$ 314,760,000
Basic Earnings Per Share															$ 1.39
Business Acquisition, Pro Forma Earnings Per Share, Diluted															$ 1.38