Acquisitions and Divestitures - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			1 Months Ended	3 Months Ended		3 Months Ended
	Sep. 30, 2012	Mar. 31, 2011 Eagle Ford And Pearsall Barnett Mercellus And Haynesville And Bossier [Member]	Apr. 30, 2012 Exxon Mobil Corporation acre Mcfe	Mar. 31, 2011 Fayetteville Shale Mcfe acre mi	Sep. 30, 2012 Permian Basin	Apr. 30, 2012 Permian Basin Mcfe	Sep. 30, 2012 Utica [Member]	Aug. 01, 2012 Utica [Member] acre	Jun. 30, 2011 Bronco Drilling Company Incorporated [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Purchase Price									$ 339
Business acquisition per share price									$ 11.00
Proceeds from Sale of Property, Plant, and Equipment	4				376		358
Current Net Production (Unit)			25,000	415,000		35,000
Net Acres Sold								72,000
Area of property sold, acres			60,000	487,000
Area of property sold, price			572
Proceeds from sale of leasehold		474		4,650
Additional assets sold, miles of pipeline				420
Portion of proceeds allocated to divestiture				350
Gain for divestiture of Fayetteville Shale midstream assets				$ 7
Maximum working interest percentage allowed	2.50%
Number of Joint Ventures	7