Business Segment Information - Financial Segment Information (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
Sep. 30, 2014 United States [Member]	Sep. 30, 2013 United States [Member]	Sep. 30, 2014 United States [Member]	Sep. 30, 2014 North Sea [Member]	Jun. 30, 2014 North Sea [Member]	Sep. 30, 2014 North Sea [Member]
Segment Reporting Information [Line Items]
Write-down of the carrying value of Oil and Gas properties	$ 1,500	$ 552	$ 1,500	$ 17	$ 203	$ 220

The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 10

-Paragraph c

-Subparagraph 4(ii)

-Article 4

Name:	us-gaap_UnamortizedCostsCapitalizedLessRelatedDeferredIncomeTaxesExceedCeilingLimitationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration