Commitments and Contingencies (Details)	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2015 USD ($) $ / MMBTU MMBTU / d	Dec. 31, 2014 USD ($)
Other Commitments [Line Items]
Rental Expense for office buildings and oil and gas operations equipment		$ 50,000,000	$ 84,000,000	$ 69,000,000
Consent Decree
Other Commitments [Line Items]
Civil penalty			4,950,000
Mitigation projects				$ 4,500,000
Supplemental environmental projects			$ 4,000,000
CONSOL Carried Cost Obligation
Other Commitments [Line Items]
Ownership interest in equity method investments (in hundredths)	50.00%		50.00%
Maximum amount to be paid each calendar year for funding of future drilling and completion costs			$ 400,000,000
Remaining obligation of joint venture's future drilling and completion costs	$ 1,600,000,000		$ 1,600,000,000
Natural gas price agreed upon benchmark, average | $ / MMBTU			4.00
Marcellus Shale Firm Transportation Agreement
Other Commitments [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d			320
Long-term Purchase Commitment, Amount			$ 1,500,000,000
Long Term Purchase Commitment, Time Period, Term			15 years
Pending Litigation | Unfavorable Regulatory Action
Other Commitments [Line Items]
Reduced penalty	$ 247,625
Maximum reduction to penalty	80.00%