Derivative Financial Instruments - Gain or Loss Recorded on Our Non-Qualifying Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	$ (95)	$ (95)
Interest Rate Contracts [Member] \| Derivative related income (expense) [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	$ (95)	$ (95)

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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=35706170&loc=SL5624171-113959

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration