|**Derivative Financial Instruments (Tables)**                                                                                    | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|-------------------------------------------------------------------------------------------------------------------------------- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Summary of Derivative Instruments [Abstract]**                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Summary of aggregate contractual or notional amounts and gross estimated fair values related to derivative financial instruments | Derivative Financial InstrumentsSeptember 30, 2013Contractual/NotionalAmountEstimated Fair Value(In millions)Asset(Liability)Without hedge designationCredit default swaps - purchased protection$20$—$—Currency forwards27—(1)Equity warrants5——Total without hedge designation52—(1)Trading activitiesFutures sold, not yet purchased17——Total$69$—$(1)December 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)
|                                                                                                                                
|                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|September 30, 2013                                                                                                               | Contractual/NotionalAmount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(In millions)                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Without hedge designation                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Credit default swaps - purchased protection                                                                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Currency forwards                                                                                                                | 27                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Equity warrants                                                                                                                  | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Total without hedge designation                                                                                                  | 52                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Trading activities                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Futures sold, not yet purchased                                                                                                  | 17                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Total                                                                                                                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|                                                                                                                                
|                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|December 31, 2012                                                                                                                | Contractual/NotionalAmount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(In millions)                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Without hedge designation                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Credit default swaps - purchased protection                                                                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Currency forwards                                                                                                                | 59                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Equity warrants                                                                                                                  | 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Total                                                                                                                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

X- DefinitionTabular disclosure of the location and fair value amounts of derivative instruments (and nonderivative instruments that are designated and qualify as hedging instruments) reported in the statement of financial position.+ ReferencesReference 1: 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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44C -Subparagraph a -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.+ Details**Name:**
                    us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock**Namespace Prefix:**
                    us-gaap_**Data Type:**
                    nonnum:textBlockItemType**Balance Type:**
                    na**Period Type:**
                    duration X- Details**Name:**
                    us-gaap_SummaryOfDerivativeInstrumentsAbstract**Namespace Prefix:**
                    us-gaap_**Data Type:**
                    xbrli:stringItemType**Balance Type:**
                    na**Period Type:**
                    duration