Impairments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012 Rigs	Sep. 30, 2012
Impaired Long-Lived Assets Held and Used [Line Items]
Lease Termination Costs	$ 25
Drilling Rigs Sold	9
Proceeds from Sale of Property, Plant, and Equipment	4
Gain on sale of natural gas gathering system and related facilities	10
Asset Impairment Charges	6	20
Land and Building | Other Operations
Impaired Long-Lived Assets Held and Used [Line Items]
Other plant, property and equipment held for sale, impairment loss recognized	7	227
Pipelines
Impaired Long-Lived Assets Held and Used [Line Items]
Other plant, property and equipment held for sale, impairment loss recognized	9
Rig Leases
Impaired Long-Lived Assets Held and Used [Line Items]
Number Of Drilling Rigs Leased		22
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	53	53
Lease Termination Costs	$ 25