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Investments (Narrative) (Details) (USD $) | Mar. 31, 2012 Y | Dec. 31, 2011 Y
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Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Fair value of securities on deposit with various regulatory authorities | $ 11,000,000 | $ 11,000,000
Fair value of securities pledged as collateral | 1,600,000,000 | 1,900,000,000
Cash pledged as collateral under investment agreements | 487,000,000 | 224,000,000
Gross unrealized losses, portfolio | 500,000,000 | 849,000,000
Gross unrealized losses, available for sale securities | 278,000,000 | 478,000,000
Rate of book value securities exceeded market value | 5.00% | 5.00%
Number of securities, unrealized loss position for continuous twelve-month period or longer | 240 | 290
Weighted average contractual maturity period of securities, unrealized loss position, years | 21 | 21
Fair value | 2,092,000,000 | 2,387,000,000
Gross unrealized losses | 278,000,000 | 478,000,000
Aggregate Unrealized Losses [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
12 months or longer, unrealized losses | 467,000,000 | 782,000,000
Variable Interest Entity [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Carrying value of available-for-sale | 856,000,000 | 432,000,000
Unrecognized gross losses | 222,000,000 | 371,000,000
Unrecognized gross gains |  | 17,000,000
Book Value Greater Than Market Value By More Than 5% [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Number of securities, unrealized loss position for continuous twelve-month period or longer | 149 | 218
Asset-Backed Securities [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Investments rated AAA | 20.00% |
Fair value | 330,000,000 |
Gross unrealized losses | (125,000,000) |
Securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 149,000,000 |
Percentage of securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 45.00% |
Asset-Backed Securities [Member] | MBIA Corp [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Benefit of guarantees provided | 149,000,000 |
Mortgage-Backed Securities [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Percentage of investments rated investment grade | 63.00% |
Investments rated AAA | 21.00% |
Fair value | 360,000,000 |
Gross unrealized losses | 91,000,000 |
Securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 250,000,000 |
Percentage of securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 69.00% |
Mortgage-Backed Securities [Member] | MBIA Corp [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Benefit of guarantees provided | 11,000,000 |
Corporate Obligations [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Percentage of investments rated investment grade | 95.00% |
Investments rated AAA | 14.00% |
Fair value | 495,000,000 |
Gross unrealized losses | 37,000,000 |
Securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 21,000,000 |
Percentage of securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 4.00% |
Corporate Obligations [Member] | MBIA Corp [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Benefit of guarantees provided | 4,000,000 |
3rd Party Guarantors [Member] | Asset-Backed Securities [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Benefit of guarantees provided | 58,000,000 |
3rd Party Guarantors [Member] | Mortgage-Backed Securities [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Benefit of guarantees provided | 230,000,000 |
3rd Party Guarantors [Member] | Corporate Obligations [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Benefit of guarantees provided | 24,000,000 |
Asset / Liability Products [Member] | Asset-Backed Securities [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Fair value | 154,000,000 |
Gross unrealized losses | $ 77,000,000 |

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