Debt (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Debt Instrument [Line Items]
Debt	$ 4,111,000,000		$ 4,123,000,000
Unamortized Discount	(14,000,000)		(15,000,000)
Total Debt, Net of Discount	4,097,000,000		4,108,000,000
Long-term Debt Due After One Year	3,723,000,000		3,736,000,000
Credit Facility due October 14, 2016 [Member]
Debt Instrument [Line Items]
Debt	0	[1]	0	[1]
Interest Rate (percentage in hundredths)	0.00%		0.00%
Debt instrument, maturity date	Oct. 14, 2016		Oct. 14, 2016
Revolving Credit Facility Maximum Borrowing Capacity	4,000,000,000
CONSOL Installment Payment, due September 30, 2013
Debt Instrument [Line Items]
Debt	328,000,000		328,000,000
Interest Rate (percentage in hundredths)	1.79%	[2]	1.79%	[2]
Debt instrument, maturity date	Sep. 30, 2013		Sep. 30, 2013
Long-Term Debt and Capital Lease Obligations, Current, net of discount	(325,000,000)		(324,000,000)
FPSO Lease Obligation
Debt Instrument [Line Items]
Debt	299,000,000		311,000,000
Interest Rate (percentage in hundredths)	0.00%		0.00%
Long-Term Debt and Capital Lease Obligations, Current, net of discount	(49,000,000)		(48,000,000)
5 1/4% Senior Notes, due April 15, 2014
Debt Instrument [Line Items]
Debt	200,000,000		200,000,000
Interest Rate (percentage in hundredths)	5.25%		5.25%
Debt instrument, maturity date	Apr. 15, 2014		Apr. 15, 2014
8 1/4% Senior Notes, due March 1, 2019
Debt Instrument [Line Items]
Debt	1,000,000,000		1,000,000,000
Interest Rate (percentage in hundredths)	8.25%		8.25%
Debt instrument, maturity date	Mar. 01, 2019		Mar. 01, 2019
4.15% Senior Notes, due December 15, 2021
Debt Instrument [Line Items]
Debt	1,000,000,000		1,000,000,000
Interest Rate (percentage in hundredths)	4.15%		4.15%
Debt instrument, maturity date	Dec. 15, 2021		Dec. 15, 2021
7¼% Senior Notes, due October 15, 2023
Debt Instrument [Line Items]
Debt	100,000,000		100,000,000
Interest Rate (percentage in hundredths)	7.25%		7.25%
Debt instrument, maturity date	Oct. 15, 2023		Oct. 15, 2023
8% Senior Notes, due April 1, 2027
Debt Instrument [Line Items]
Debt	250,000,000		250,000,000
Interest Rate (percentage in hundredths)	8.00%		8.00%
Debt instrument, maturity date	Apr. 01, 2027		Apr. 01, 2027
6% Senior Notes, due March 1, 2041
Debt Instrument [Line Items]
Debt	850,000,000		850,000,000
Interest Rate (percentage in hundredths)	6.00%		6.00%
Debt instrument, maturity date	Mar. 01, 2041		Mar. 01, 2041
7 1/4% Senior Debentures, due August 1, 2097
Debt Instrument [Line Items]
Debt	$ 84,000,000		$ 84,000,000
Interest Rate (percentage in hundredths)	7.25%		7.25%
Debt instrument, maturity date	Aug. 01, 2097		Aug. 01, 2097

[1] Our Credit Agreement provides for a $4.0 billion unsecured revolving Credit Facility. The Credit Facility is available for general corporate purposes.

[2] Imputed rate based on the prevailing market rates for similar debt instruments at the date of assessment.