Fair Value Measurement - Supplemental Caption Data (Details 1a) (USD $) In Millions, unless otherwise specified			3 Months Ended
Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Available-for-sale Securities [Member]	Mar. 31, 2011 Available-for-sale Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Level Three Liabilities As Percentage Of Total Firm Liabilities At Fair Value	19.00%	21.00%
Realized gains and losses recorded in income on AFS securities			$ 96	$ 330
Unrealized gains and losses recorded in OCI on AFS securities			$ (85)	$ 156

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity).

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration