Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2015
Commitment And Contingencies [Line Items]
Accrued liability for legal contingencies	$ 23,000,000
Undiscounted reserve for environmental remediation	63,000,000
Minimum [Member] \| Apollo Exploration Lawsuit [Member]
Commitment And Contingencies [Line Items]
Plaintiffs alleged damages	$ 1,100,000,000

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration