Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended
	Nov. 30, 2010	Sep. 30, 2014	Dec. 31, 2013
Long-term Purchase Commitment [Line Items]
Total future drilling commitments at balance sheet date		$ 675
Drilling commitments due remainder of current year		66
Drilling commitments Year Two		246
Drilling Commitments Year Three		213
Drilling Commitments Year Four		122
Drilling Commitments Year Five		28
Future Drilling Commitments End Date		2018-07
Loss related to contingency damages	165
Legal proceedings recorded as a liability under other noncurrent liabilities		(2.9)	(1.7)
Pipeline Transportation Commitments [Member]
Long-term Purchase Commitment [Line Items]
Purchase commitment, end date		2025
Purchase commitment, total		1,000
Purchase commitment, due in remainder of current year		40
Purchase commitment, due second year		181
Purchase commitment, due third year		186
Purchase commitment, due fourth year		180
Purchase commitment, due fifth year		175
Purchase commitment, due after fifth year		241
Non-operational [Member]
Long-term Purchase Commitment [Line Items]
Crude oil non-op transportation commitment, total		260
Cost Sharing Commitment [Member]
Long-term Purchase Commitment [Line Items]
Purchase commitment, end date		2016
Purchase commitment, total		13
Purchase commitment, due in remainder of current year		3
Purchase commitment, due second year		8
Purchase commitment, due third year		$ 2