Fair Values of Assets and Liabilities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Fair Value Inputs Assets Quantitative Information [Abstract]
Fair value measurement transfers from one level to another	$ 0	$ 0
Mortgage loans held for sale measured at fair value gain (loss)	(175)	19
Assumed minimum credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts	0.00%
Assumed maximum credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts	99.00%
Assumed average credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts	8.00%
Carrying value of unfunded commitments and standby letters of credit	421		415
Carrying value of other guarantees	$ 436		$ 452

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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- Details

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- Definition

Fair value measurement transfers from one level to another.

+ References

No definition available.

+ Details

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- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 30

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

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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.

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