Accounting for Suspended Exploratory Wells (Details) (USD $)	Mar. 31, 2013
Accounting for Suspended Exploratory Wells [Abstract]
Capitalized cost of exploratory wells	$ 2,900,000,000
Change in capitalized cost of suspended wells from the prior year end	$ 220,000,000

The amount of capitalized exploratory well costs that is pending the determination of proved reserves. This does not include amounts that were capitalized and subsequently expensed in the same annual period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS19-1

-Paragraph 10

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_CapitalizedExploratoryWellCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant