|**Derivative Financial Instruments (Tables)**                                                                                    | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
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|**Summary of Derivative Instruments [Abstract]**                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Summary of recognized gains (losses) related to derivative financial instruments                                                 | Recognized Gains (Losses)Years ended December 31(In millions)201220112010Without hedge designationCurrency forwards$(2)$—$—Credit default swaps - purchased protection——(1)Total without hedge designation(2)—(1)Trading activitiesFutures sold, not yet purchased——(1)Total$(2)$—$(2)                                                                                                                                                                                                        
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|Years ended December 31                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(In millions)                                                                                                                    | 2012                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Without hedge designation                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Currency forwards                                                                                                                | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Credit default swaps - purchased protection                                                                                      | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Total without hedge designation                                                                                                  | (2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Trading activities                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Futures sold, not yet purchased                                                                                                  | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Total                                                                                                                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Summary of aggregate contractual or notional amounts and gross estimated fair values related to derivative financial instruments | Derivative Financial InstrumentsDecember 31, 2012Contractual/NotionalAmountEstimated Fair Value(In millions)Asset(Liability)Without hedge designationCredit default swaps - purchased protection$20$—$(1)Currency forwards59—(2)Equity warrants5——Total$84$—$(3)December 31, 2011Contractual/NotionalAmountEstimated Fair Value(In millions)Asset(Liability)Without hedge designationCredit default swaps - purchased protection$20$—$(1)Currency forwards221—Equity warrants4——Total$46$1$(1)
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|December 31, 2012                                                                                                                | Contractual/NotionalAmount                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|(In millions)                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Without hedge designation                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Credit default swaps - purchased protection                                                                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Currency forwards                                                                                                                | 59                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Equity warrants                                                                                                                  | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Total                                                                                                                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
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|                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|December 31, 2011                                                                                                                | Contractual/NotionalAmount                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|(In millions)                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Without hedge designation                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Credit default swaps - purchased protection                                                                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Currency forwards                                                                                                                | 22                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Equity warrants                                                                                                                  | 4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Total                                                                                                                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

X- DefinitionTabular disclosure of the location and amount of gains and losses reported in the statement of financial performance, or when applicable, the statement of financial position. For example,  (a) gains and losses recognized in the income statement on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges and (b) gains and losses initially recognized in other comprehensive income on derivative instruments designated and qualifying as cash flow hedges.+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 205G -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44C -Subparagraph b -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959+ Details**Name:**
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