Schedule of Interest Income and Interest Expense (Parenthetical) (Detail) (Variable Interest Entity, Not Primary Beneficiary, USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Variable Interest Entity, Not Primary Beneficiary
Amounts Related To Interest [Line Items]
Interest expense and interest income excluded, amount	$ (15)	$ (13)	$ (35)	$ (39)

The amount of income (loss) from operations derived by the reporting entity during the period from the Variable Interest Entity (VIE).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph d

-URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5747-111685

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS140-4/FIN46(R)-8

-Paragraph C8

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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_VariableInterestEntityActivityBetweenVIEAndEntityOperatingIncomeOrLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration