Acquisitions and Divestitures - Additional Information - 2014 Activity - Canada Divestiture (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	1 Months Ended	0 Months Ended
	Jun. 30, 2014	Dec. 31, 2014	Apr. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of oil and gas assets		$ 1,300
Effective date of sale	May 01, 2014	Oct. 01, 2014
Natural Gas [Member] | Canada [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of oil and gas assets			$ 374
Natural gas properties sold			328,400
Effective date of sale			Jan. 01, 2014
Natural Gas Liquids [Member] | Wapiti Canada [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Working interest percentage			100.00%