Impact of Changes in Fair Value of Interest Rate Swaps and Underlying Hedged Items on Results of Operations (Detail) (Interest expense [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest expense [Member]
Derivatives, Fair Value [Line Items]
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments		$ 25	$ (1)	$ 37
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge		$ (25)	$ 1	$ (37)

Amount of unrealized gain (loss) included in earnings related to the fair value of the hedged item in an interest rate fair value hedge, offset by the gain (loss) on the hedging instrument to the extent that the fair value hedge is determined to be effective.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (a)

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

Name:	us-gaap_IncreaseDecreaseInFairValueOfHedgedItemInInterestRateFairValueHedge1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration