Fair Values of Assets and Liabilities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value measurement transfers from one level to another	$ 0	$ 0	$ 0
Mortgage loans held for sale measured at fair value gain losses	287	15	(125)
Carrying value of unfunded commitments and standby letters of credit	415	381
Carrying value of other guarantees	$ 452	$ 359
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assumed minimum credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts	0.00%
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assumed maximum credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts	90.00%
Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assumed average credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts	7.00%

Assumed average credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts.

No definition available.

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- Definition

Assumed maximum credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts.

+ References

No definition available.

+ Details

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- Definition

Assumed minimum credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts.

+ References

No definition available.

+ Details

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- Definition

Carrying value of unfunded commitments and standby letters of credit.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Fair value measurement transfers from one level to another.

+ References

No definition available.

+ Details

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- Definition

Mortgage loans held for sale measured at fair value gain losses.

+ References

No definition available.

+ Details

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- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9

-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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph c

-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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