Oil and Natural Gas Property Transactions - Narrative (Details)	6 Months Ended		60 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2013 Resource_Plays Joint_Venture
Business Acquisition [Line Items]
Proceeds from divestitures of proved and unproved properties	$ 14,000,000	$ 248,000,000
Corporate Joint Venture [Member]
Business Acquisition [Line Items]
Proceeds from divestitures of proved and unproved properties		240,000,000
Number of Joint Ventures | Joint_Venture			8
Number of Resource Plays | Resource_Plays			8
Proceeds from Divestiture of Interest in Joint Venture	8,000,000,000
Total Drilling Carries	9,000,000,000
Oil And Gas Benefit From Drilling Carries	51,000,000	357,000,000
Corporate Joint Venture [Member] | Minimum [Member]
Business Acquisition [Line Items]
Interest Sold			20.00%
Corporate Joint Venture [Member] | Maximum [Member]
Business Acquisition [Line Items]
Interest Sold			50.00%
JV Marcellus, Barnett, Utica, Eagle Ford, Mid-Continent [Member]
Business Acquisition [Line Items]
Proceeds from Divestiture of Interest in Joint Venture	19,000,000	$ 8,000,000
Corporate VPP [Member]
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Other Assets	$ 0