Derivative Financial Instruments - Gain or Loss Recorded on Our Non-Qualifying Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	$ 83	$ 208
Interest Rate Contracts [Member] \| Derivative related income (expense) [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	83	212
Currency contracts [Member] \| Derivative related income (expense) [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	$ 0	$ (4)

Net gain (loss) from the increase (decrease) in fair value of derivative instrument not designated as hedging instrument.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 45

-Subparagraph b(1)(b)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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