Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2013
Debt Instrument
Issue of senior notes to third party investors	$ 1,300,000,000
Beginning Amount
Debt Instrument
Global Bank Note Program	20,000,000,000
Ending Amount
Debt Instrument
Global Bank Note Program	25,000,000,000
Parent company \| Senior Debt Obligations \| Fixed Rate 1.45 Percent Notes Due 2018
Debt Instrument
Issue of senior notes to third party investors	600,000,000
Maturity date	February 28, 2018
Parent company \| Senior Debt Obligations \| Fixed Rate Point .90 Percent Notes Due 2016
Debt Instrument
Issue of senior notes to third party investors	400,000,000
Maturity date	February 26, 2016
Parent company \| Senior Debt Obligations \| Floating Rate Notes Due 2016 \| Three Month LIBOR
Debt Instrument
Issue of senior notes to third party investors	$ 300,000,000
Maturity date	February 26, 2016
Debt Instrument, Interest Rate Terms	3-month LIBOR plus 41 basis points

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration