Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell - Additional Information (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets Sold under Agreements to Repurchase [Line Items]
Collateral Requirements Minimum Percentage Collateral To Fair Value Of Securities Purchased Under Repurchase Agreements	95.00%
Collateral Requirements Maximum Percentage Collateral To Fair Value Of Securities Purchased Under Repurchase Agreements	110.00%
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	$ 1,100	$ 806
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 246	$ 247

Collateral Requirements Maximum Percentage Collateral To Fair Value Of Securities Purchased Under Repurchase Agreements

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- Definition

Collateral Requirements, Minimum Percentage, Collateral To Fair Value Of Securities Purchased Under Repurchase Agreements

+ References

No definition available.

+ Details

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- Definition

This is the fair value as of the date of each statement of financial position presented of the collateral that is permitted, by contact or custom, to be sold or re-pledged.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 17

-Subparagraph a(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

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- Definition

Fair value as of the balance sheet date of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used (generally under repurchase agreements, securities lending agreements or to cover short sales).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

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