Derivative Financial Instruments - Derivatives Related to Fair Value Option Debt Financial Position (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Total Asset fair value hedges	$ 0	$ 7
Total liability fair value hedges	0	0
Interest rate swaps [Member] \| Derivative financial assets [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps, Derivative financial assets at fair value	0	7
Interest rate swaps [Member] \| Derivative Related Liabilities [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps, Derivative related liabilities at fair value	0	0
Currency swaps [Member] \| Derivative financial assets [Member]
Derivatives, Fair Value [Line Items]
Currency swaps, Derivative finacial assets at fair value	0	0
Currency swaps [Member] \| Derivative Related Liabilities [Member]
Derivatives, Fair Value [Line Items]
Currency swaps, Derivative related liabilities at fair value	0	0
Debt option [Member]
Derivatives, Fair Value [Line Items]
Total Asset fair value hedges	924	1,147
Total liability fair value hedges
Debt option [Member] \| Interest rate swaps [Member] \| Derivative financial assets [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps, Derivative financial assets at fair value	412	469
Debt option [Member] \| Interest rate swaps [Member] \| Derivative Related Liabilities [Member]
Derivatives, Fair Value [Line Items]
Interest rate swaps, Derivative related liabilities at fair value
Debt option [Member] \| Currency swaps [Member] \| Derivative financial assets [Member]
Derivatives, Fair Value [Line Items]
Currency swaps, Derivative finacial assets at fair value	512	678
Debt option [Member] \| Currency swaps [Member] \| Derivative Related Liabilities [Member]
Derivatives, Fair Value [Line Items]
Currency swaps, Derivative related liabilities at fair value

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Fair value of all derivative assets designated as fair value hedging instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

+ Details

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- Definition

Fair value of all derivative liabilities designated as fair value hedging instruments.

+ References

+ Details

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- Definition

Fair value as of the balance sheet date of all derivative assets designated as foreign currency fair value hedging instruments.

+ References

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- Definition

Fair value as of the balance sheet date of all derivative liabilities designated as foreign currency fair value hedging instruments.

+ References

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- Definition

Fair value as of the balance sheet date of all derivative assets designated as interest rate fair value hedging instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 17

-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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- Definition

Fair value as of the balance sheet date of all derivative liabilities designated as interest rate fair value hedging instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 17

-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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