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Fair Value Measurement- Details of Certain Items Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale $ 285 [1] $ 279 [1]
Alt-A RMBS | 2006-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 117 [1] 111 [1]
Alt-A RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 109 [1] 107 [1]
Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 59 [1] 61 [1]
Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 616 [1] 728 [1]
Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 160 [1] 215 [1]
Prime RMBS | 2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 102 [1] 106 [1]
Prime RMBS | 2006
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 63 [1] 70 [1]
Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 291 [1] 337 [1]
Subprime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 436 [1] 452 [1]
Subprime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 111 [1] 108 [1]
Subprime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 325 [1] 344 [1]
Commercial MBS | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 2,747 [1] 2,839 [1]
Commercial MBS | 2005 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 618 [1] 640 [1]
Commercial MBS | 2009-2012 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 322 [1] 283 [1]
Commercial MBS | 2008 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 24 [1] 24 [1]
Commercial MBS | 2007 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 682 [1] 707 [1]
Commercial MBS | 2006 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 834 [1] 900 [1]
Commercial MBS | 2004 and earlier | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 267 [1] 285 [1]
Foreign covered bonds
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 3,390 [1] 3,718 [1]
Foreign covered bonds | Canada
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 869 [1] 925 [1]
Foreign covered bonds | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 624 [1] 866 [1]
Foreign covered bonds | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 732 [1] 756 [1]
Foreign covered bonds | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 282 [1] 360 [1]
Foreign covered bonds | Other
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 883 [1] 811 [1]
Sovereign Debt
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 10,088 [1] 9,424 [1]
Sovereign Debt | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 2,204 [1] 1,646 [1]
Sovereign Debt | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 4,487 [1] 4,771 [1]
Sovereign Debt | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 1,990 [1] 2,054 [1]
Sovereign Debt | Other
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 55 [1] 56 [1]
Sovereign Debt | France
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 1,352 [1] 897 [1]
Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 1,968 [1],[2] 1,970 [1],[2]
Alt-A RMBS | 2006-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 1,138 [1],[2] 1,128 [1],[2]
Alt-A RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 615 [1],[2] 622 [1],[2]
Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 215 [1],[2] 220 [1],[2]
Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 981 [1],[2] 1,010 [1],[2]
Prime RMBS | 2006-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 586 [1],[2] 601 [1],[2]
Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 366 [1],[2] 378 [1],[2]
Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 29 [1],[2] 31 [1],[2]
Sub Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 134 [1],[2] 130 [1],[2]
Sub Prime RMBS | 2005-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 98 [1],[2] 94 [1],[2]
Sub Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 36 [1],[2] 36 [1],[2]
Available-for-sale | European floating rate notes
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 2,874 [1] 3,145 [1]
Available-for-sale | European floating rate notes | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 63 [1] 68 [1]
Available-for-sale | European floating rate notes | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 1,657 [1] 1,873 [1]
Available-for-sale | European floating rate notes | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 812 [1] 841 [1]
Available-for-sale | European floating rate notes | Ireland
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 157 [1] 161 [1]
Available-for-sale | European floating rate notes | Italy
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale 116 [1] 125 [1]
Available-for-sale | European floating rate notes | Australia
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Available-for-sale $ 69 [1] $ 77 [1]
Ratings, AAA/AA- | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% 1.00%
Ratings, AAA/AA- | Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 3.00% 4.00%
Ratings, AAA/AA- | Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 5.00% 7.00%
Ratings, AAA/AA- | Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, AAA/AA- | Prime RMBS | 2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, AAA/AA- | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 9.00% 16.00%
Ratings, AAA/AA- | Subprime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 2.00% 3.00%
Ratings, AAA/AA- | Subprime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% 4.00%
Ratings, AAA/AA- | Subprime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 2.00% 3.00%
Ratings, AAA/AA- | Commercial MBS | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 88.00% 89.00%
Ratings, AAA/AA- | Commercial MBS | 2005 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 98.00% 98.00%
Ratings, AAA/AA- | Commercial MBS | 2009-2012 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 93.00% 97.00%
Ratings, AAA/AA- | Commercial MBS | 2008 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 59.00% 59.00%
Ratings, AAA/AA- | Commercial MBS | 2007 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 78.00% 78.00%
Ratings, AAA/AA- | Commercial MBS | 2006 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 85.00% 85.00%
Ratings, AAA/AA- | Commercial MBS | 2004 and earlier | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 96.00% 100.00%
Ratings, AAA/AA- | Foreign covered bonds
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Foreign covered bonds | Canada
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Foreign covered bonds | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 98.00% 98.00%
Ratings, AAA/AA- | Foreign covered bonds | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Foreign covered bonds | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Foreign covered bonds | Other
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Sovereign Debt
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Sovereign Debt | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Sovereign Debt | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Sovereign Debt | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Sovereign Debt | Other
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Sovereign Debt | France
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% [2] 1.00% [2]
Ratings, AAA/AA- | Alt-A RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% 4.00% [2]
Ratings, AAA/AA- | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00% [2]
Ratings, AAA/AA- | Sub Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% [2] 2.00% [2]
Ratings, AAA/AA- | Sub Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% [2] 5.00% [2]
Ratings, AAA/AA- | Available-for-sale | European floating rate notes
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 80.00% 77.00%
Ratings, AAA/AA- | Available-for-sale | European floating rate notes | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, AAA/AA- | Available-for-sale | European floating rate notes | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 84.00% 79.00%
Ratings, AAA/AA- | Available-for-sale | European floating rate notes | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, AAA/AA- | Available-for-sale | European floating rate notes | Ireland
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 16.00% 15.00%
Ratings, AAA/AA- | Available-for-sale | European floating rate notes | Italy
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, AAA/AA- | Available-for-sale | European floating rate notes | Australia
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 94.00% 94.00%
Ratings, A+/A- | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 2.00% 2.00%
Ratings, A+/A- | Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 9.00% 9.00%
Ratings, A+/A- | Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 31.00% 29.00%
Ratings, A+/A- | Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 43.00% 33.00%
Ratings, A+/A- | Prime RMBS | 2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, A+/A- | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 42.00% 42.00%
Ratings, A+/A- | Subprime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 5.00% 5.00%
Ratings, A+/A- | Subprime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 8.00% 8.00%
Ratings, A+/A- | Subprime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 5.00% 4.00%
Ratings, A+/A- | Commercial MBS | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 10.00% 9.00%
Ratings, A+/A- | Commercial MBS | 2005 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% 1.00%
Ratings, A+/A- | Commercial MBS | 2009-2012 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 7.00% 3.00%
Ratings, A+/A- | Commercial MBS | 2008 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 41.00% 41.00%
Ratings, A+/A- | Commercial MBS | 2007 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 16.00% 16.00%
Ratings, A+/A- | Commercial MBS | 2006 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 15.00% 14.00%
Ratings, A+/A- | Commercial MBS | 2004 and earlier | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 4.00% 0.00%
Ratings, A+/A- | Foreign covered bonds | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 2.00% 2.00%
Ratings, A+/A- | Foreign covered bonds | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% 0.00%
Ratings, A+/A- | Foreign covered bonds | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00%  
Ratings, A+/A- | Sovereign Debt | Other
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, A+/A- | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% [2]  
Ratings, A+/A- | Alt-A RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 4.00%  
Ratings, A+/A- | Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% [2] 2.00% [2]
Ratings, A+/A- | Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% [2] 1.00% [2]
Ratings, A+/A- | Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% [2] 1.00% [2]
Ratings, A+/A- | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 7.00% [2] 8.00% [2]
Ratings, A+/A- | Sub Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% 0.00% [2]
Ratings, A+/A- | Sub Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 5.00% [2] 0.00% [2]
Ratings, A+/A- | Available-for-sale | European floating rate notes
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 13.00% 15.00%
Ratings, A+/A- | Available-for-sale | European floating rate notes | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 3.00% 9.00%
Ratings, A+/A- | Available-for-sale | European floating rate notes | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 16.00% 19.00%
Ratings, A+/A- | Available-for-sale | European floating rate notes | Netherlands
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, A+/A- | Available-for-sale | European floating rate notes | Ireland
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, A+/A- | Available-for-sale | European floating rate notes | Italy
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, A+/A- | Available-for-sale | European floating rate notes | Australia
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 6.00% 6.00%
Ratings, BBB+/BBB- | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 5.00% 6.00%
Ratings, BBB+/BBB- | Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 25.00% 25.00%
Ratings, BBB+/BBB- | Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 11.00% 12.00%
Ratings, BBB+/BBB- | Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% 7.00%
Ratings, BBB+/BBB- | Prime RMBS | 2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 45.00% 45.00%
Ratings, BBB+/BBB- | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 8.00% 7.00%
Ratings, BBB+/BBB- | Subprime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 14.00% 13.00%
Ratings, BBB+/BBB- | Subprime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 37.00% 34.00%
Ratings, BBB+/BBB- | Subprime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 6.00% 6.00%
Ratings, BBB+/BBB- | Commercial MBS | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 2.00% 2.00%
Ratings, BBB+/BBB- | Commercial MBS | 2005 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% 1.00%
Ratings, BBB+/BBB- | Commercial MBS | 2007 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 6.00% 6.00%
Ratings, BBB+/BBB- | Commercial MBS | 2006 | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% 1.00%
Ratings, BBB+/BBB- | Commercial MBS | 2004 and earlier | Domestic
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, BBB+/BBB- | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 2.00% [2] 2.00% [2]
Ratings, BBB+/BBB- | Alt-A RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% [2] 1.00% [2]
Ratings, BBB+/BBB- | Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 13.00% [2] 12.00% [2]
Ratings, BBB+/BBB- | Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% [2] 1.00% [2]
Ratings, BBB+/BBB- | Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 1.00% [2] 2.00% [2]
Ratings, BBB+/BBB- | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 24.00% [2] 24.00% [2]
Ratings, BBB+/BBB- | Sub Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 10.00% [2] 10.00% [2]
Ratings, BBB+/BBB- | Sub Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 37.00% [2] 36.00% [2]
Ratings, BBB+/BBB- | Available-for-sale | European floating rate notes
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 0.00% 2.00%
Ratings, BBB+/BBB- | Available-for-sale | European floating rate notes | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, BBB+/BBB- | Available-for-sale | European floating rate notes | United Kingdom
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   2.00%
Ratings, BBB+/BBB- | Available-for-sale | European floating rate notes | Ireland
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent)   0.00%
Ratings, BB+ and lower | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 92.00% 91.00%
Ratings, BB+ and lower | Alt-A RMBS | 2006-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, BB+ and lower | Alt-A RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, BB+ and lower | Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 63.00% 62.00%
Ratings, BB+ and lower | Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 53.00% 52.00%
Ratings, BB+ and lower | Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 57.00% 60.00%
Ratings, BB+ and lower | Prime RMBS | 2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 55.00% 55.00%
Ratings, BB+ and lower | Prime RMBS | 2006
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% 100.00%
Ratings, BB+ and lower | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 41.00% 35.00%
Ratings, BB+ and lower | Subprime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 79.00% 79.00%
Ratings, BB+ and lower | Subprime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 55.00% 54.00%
Ratings, BB+ and lower | Subprime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 87.00% 87.00%
Ratings, BB+ and lower | Alt-A RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 97.00% [2] 97.00% [2]
Ratings, BB+ and lower | Alt-A RMBS | 2006-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% [2] 100.00% [2]
Ratings, BB+ and lower | Alt-A RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 95.00% [2] 95.00% [2]
Ratings, BB+ and lower | Alt-A RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 87.00% [2] 86.00% [2]
Ratings, BB+ and lower | Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 99.00% [2] 98.00% [2]
Ratings, BB+ and lower | Prime RMBS | 2006-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% [2] 100.00% [2]
Ratings, BB+ and lower | Prime RMBS | 2005
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 98.00% [2] 97.00% [2]
Ratings, BB+ and lower | Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 69.00% [2] 68.00% [2]
Ratings, BB+ and lower | Sub Prime RMBS
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 89.00% [2] 88.00% [2]
Ratings, BB+ and lower | Sub Prime RMBS | 2005-2007
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 100.00% [2] 100.00% [2]
Ratings, BB+ and lower | Sub Prime RMBS | 2004 and earlier
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 57.00% [2] 59.00% [2]
Ratings, BB+ and lower | Available-for-sale | European floating rate notes
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 7.00% 6.00%
Ratings, BB+ and lower | Available-for-sale | European floating rate notes | Germany
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 97.00% 91.00%
Ratings, BB+ and lower | Available-for-sale | European floating rate notes | Ireland
    
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]    
Percentage Of Fair Value (percent) 84.00% 85.00%
[1] At March 31, 2013 and Dec. 31, 2012, foreign covered bonds were included in Level 1 and Level 2 in the valuation hierarchy. All other assets in the table are Level 2 assets in the valuation hierarchy.
[2] Previously included in the Grantor Trust.