Fair Value Measurement - Changes in Level 3, Supplemental Caption Data (Details 2a) (USD $) In Millions, unless otherwise specified			3 Months Ended
Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Available-for-sale Securities	Mar. 31, 2012 Available-for-sale Securities
Fair Value, Option, Quantitative Disclosures
Level Three Liabilities As Percentage Of Total Firm Liabilities At Fair Value	19.00%	19.00%
Realized gains and losses recorded in income on AFS securities			$ (18)	$ 96
Unrealized gains and losses recorded in OCI on AFS securities			$ 14	$ (85)

Level 3 liabilities as a percentage of total firm liabilities at fair value.

No definition available.

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- Definition

Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

+ Details

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- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1a)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

+ Details

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