Organization and Business (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended					0 Months Ended
	Jun. 30, 2013 item	Oct. 02, 2012 10.75% senior unsecured notes	May 31, 2013 9.25% senior unsecured notes	Oct. 02, 2012 Eagle Property Acquisition	Oct. 02, 2012 Eagle Property Acquisition 10.75% senior unsecured notes	Oct. 02, 2012 Eagle Property Acquisition Series A Preferred Stock	May 31, 2013 Anadarko Basin Acquisition 9.25% senior unsecured notes Panther Energy Company, LLC and its partners
Acquisition information
Purchase price, cash				$ 325			$ 618
Purchase price, preferred shares						325,000
Liquidation value (in dollars per share)						$ 1,000
Aggregate principal amount borrowed		$ 600	$ 700	$ 600	$ 600		$ 700
Interest rate (as a percent)		10.75%	9.25%		10.75%		9.25%
Segment information
Number of reportable segments	1