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Investments (Fair Values And Gross Unrealized Losses By Credit Rating Category Of Mortgage Backed Securities) (Details) (USD $)
In Millions
Sep. 30, 2011
Dec. 31, 2010
Investment [Line Items]  
Total, Fair Value$ 2,549$ 6,954
Total, Unrealized Losses567804
Mortgage-Backed Securities [Member] | Aaa [Member] | Commercial Mortgage-Backed [Member]
  
Investment [Line Items]  
Total, Fair Value2 
Mortgage-Backed Securities [Member] | Aa [Member] | Commercial Mortgage-Backed [Member]
  
Investment [Line Items]  
Total, Fair Value1 
Mortgage-Backed Securities [Member] | A [Member] | Commercial Mortgage-Backed [Member]
  
Investment [Line Items]  
Total, Fair Value4 
Mortgage-Backed Securities [Member] | Baa [Member] | Commercial Mortgage-Backed [Member]
  
Investment [Line Items]  
Total, Fair Value25 
Total, Unrealized Losses(6) 
Mortgage-Backed Securities [Member] | Below Investment Grade [Member] | Commercial Mortgage-Backed [Member]
  
Investment [Line Items]  
Total, Fair Value2 
Total, Unrealized Losses(1) 
Mortgage-Backed Securities [Member] | Not Rated [Member] | Commercial Mortgage-Backed [Member]
  
Investment [Line Items]  
Total, Unrealized Losses  
Mortgage-Backed Securities [Member] | Commercial Mortgage-Backed [Member]
  
Investment [Line Items]  
Total, Fair Value34 
Total, Unrealized Losses(7) 
Mortgage-Backed Securities [Member] | Aaa [Member] | Residential Mortgage-Backed Securities [Member] | Collateralized [Member]
  
Investment [Line Items]  
Total, Fair Value66 
Total, Unrealized Losses(1) 
Mortgage-Backed Securities [Member] | Aaa [Member] | Residential Mortgage-Backed Securities [Member] | Home Equity [Member]
  
Investment [Line Items]  
Total, Fair Value3 
Mortgage-Backed Securities [Member] | Aaa [Member] | Residential Mortgage-Backed Securities [Member] | Pass-Through Securities [Member]
  
Investment [Line Items]  
Total, Fair Value22 
Mortgage-Backed Securities [Member] | Aa [Member] | Residential Mortgage-Backed Securities [Member] | Collateralized [Member]
  
Investment [Line Items]  
Total, Fair Value45 
Total, Unrealized Losses(10) 
Mortgage-Backed Securities [Member] | Aa [Member] | Residential Mortgage-Backed Securities [Member] | Home Equity [Member]
  
Investment [Line Items]  
Total, Fair Value81 
Total, Unrealized Losses(25) 
Mortgage-Backed Securities [Member] | Aa [Member] | Residential Mortgage-Backed Securities [Member] | Other RMBS [Member]
  
Investment [Line Items]  
Total, Fair Value17 
Total, Unrealized Losses(4) 
Mortgage-Backed Securities [Member] | A [Member] | Residential Mortgage-Backed Securities [Member] | Collateralized [Member]
  
Investment [Line Items]  
Total, Fair Value10 
Total, Unrealized Losses(1) 
Mortgage-Backed Securities [Member] | A [Member] | Residential Mortgage-Backed Securities [Member] | Home Equity [Member]
  
Investment [Line Items]  
Total, Fair Value1 
Mortgage-Backed Securities [Member] | Baa [Member] | Residential Mortgage-Backed Securities [Member] | Collateralized [Member]
  
Investment [Line Items]  
Total, Fair Value2 
Mortgage-Backed Securities [Member] | Below Investment Grade [Member] | Residential Mortgage-Backed Securities [Member] | Collateralized [Member]
  
Investment [Line Items]  
Total, Fair Value51 
Total, Unrealized Losses(26) 
Mortgage-Backed Securities [Member] | Below Investment Grade [Member] | Residential Mortgage-Backed Securities [Member] | Home Equity [Member]
  
Investment [Line Items]  
Total, Fair Value87 
Total, Unrealized Losses(43) 
Mortgage-Backed Securities [Member] | Below Investment Grade [Member] | Residential Mortgage-Backed Securities [Member] | Other RMBS [Member]
  
Investment [Line Items]  
Total, Fair Value8 
Total, Unrealized Losses(4) 
Mortgage-Backed Securities [Member] | Not Rated [Member] | Residential Mortgage-Backed Securities [Member] | Collateralized [Member]
  
Investment [Line Items]  
Total, Unrealized Losses  
Mortgage-Backed Securities [Member] | Not Rated [Member] | Residential Mortgage-Backed Securities [Member] | Home Equity [Member]
  
Investment [Line Items]  
Total, Fair Value23 
Total, Unrealized Losses  
Mortgage-Backed Securities [Member] | Not Rated [Member] | Residential Mortgage-Backed Securities [Member] | Pass-Through Securities [Member]
  
Investment [Line Items]  
Total, Unrealized Losses  
Mortgage-Backed Securities [Member] | Not Rated [Member] | Residential Mortgage-Backed Securities [Member] | Other RMBS [Member]
  
Investment [Line Items]  
Total, Unrealized Losses  
Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member] | Collateralized [Member]
  
Investment [Line Items]  
Total, Fair Value174 
Total, Unrealized Losses(38) 
Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member] | Home Equity [Member]
  
Investment [Line Items]  
Total, Fair Value195 
Total, Unrealized Losses(68) 
Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member] | Pass-Through Securities [Member]
  
Investment [Line Items]  
Total, Fair Value22 
Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member] | Other RMBS [Member]
  
Investment [Line Items]  
Total, Fair Value25 
Total, Unrealized Losses(8) 
Mortgage-Backed Securities [Member]
  
Investment [Line Items]  
Total, Fair Value450 
Total, Unrealized Losses(121) 
Mortgage-Backed Securities [Member] | MBIA [Member]
  
Investment [Line Items]  
Total, Fair Value18[1] 
Total, Unrealized Losses(5)[1] 
Mortgage-Backed Securities [Member] | Aaa [Member]
  
Investment [Line Items]  
Total, Fair Value93 
Total, Unrealized Losses(1) 
Mortgage-Backed Securities [Member] | Aa [Member]
  
Investment [Line Items]  
Total, Fair Value144 
Total, Unrealized Losses(39) 
Mortgage-Backed Securities [Member] | A [Member]
  
Investment [Line Items]  
Total, Fair Value15 
Total, Unrealized Losses(1) 
Mortgage-Backed Securities [Member] | Baa [Member]
  
Investment [Line Items]  
Total, Fair Value27 
Total, Unrealized Losses(6) 
Mortgage-Backed Securities [Member] | Below Investment Grade [Member]
  
Investment [Line Items]  
Total, Fair Value148 
Total, Unrealized Losses(74) 
Mortgage-Backed Securities [Member] | Not Rated [Member]
  
Investment [Line Items]  
Total, Fair Value23 
Total, Unrealized Losses  
[1]Includes investments insured by MBIA Corp. and National.