|**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)201120102009Without hedge designationInterest rate swaps$—$—$61Credit default swaps - purchased protection—(1)(47)Credit default swaps - sold protection——3Total return swaps——(2)Futures sold, not yet purchased——21Options written——15Total without hedge designation—(1)51Trading activitiesFutures sold, not yet purchased—(1)(2)Total$—$(2)$49                                                                                                                     
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|Years ended December 31                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|(In millions)                                                                                                                    | 2011                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Without hedge designation                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Interest rate swaps                                                                                                              | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Credit default swaps - purchased protection                                                                                      | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Credit default swaps - sold protection                                                                                           | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Total return swaps                                                                                                               | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Futures sold, not yet purchased                                                                                                  | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Options written                                                                                                                  | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Total without hedge designation                                                                                                  | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|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, 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)December 31, 2010Contractual/NotionalAmountEstimated Fair Value(In millions)Asset(Liability)Without hedge designationCredit default swaps - purchased protection$20$—$(2)Credit default swaps - sold protection81—Currency forwards18——Equity warrants3——Total$49$1$(2)
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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                                                                                                                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
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|                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|December 31, 2010                                                                                                                | Contractual/NotionalAmount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|(In millions)                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Without hedge designation                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Credit default swaps - purchased protection                                                                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Credit default swaps - sold protection                                                                                           | 8                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Currency forwards                                                                                                                | 18                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Equity warrants                                                                                                                  | 3                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|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 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 4C -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624171-113959Reference 3: 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=6935481&loc=SL5618551-113959Reference 4: 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.+ Details**Name:**
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