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Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value of securities on deposit with various regulatory authorities | $ 11 |  | $ 11 |
Fair value of securities pledged as collateral | 1,900 |  | 2,400 |
Unrecognized gross gains | 17 |  |  |
Gross unrealized losses, portfolio | 849 |  | 1,100 |
Percentage of book value securities exceeded market value | 5.00% |  | 5.00% |
Number of securities, unrealized loss position for continuous 12-month period or longer | 290 |  | 412 |
Weighted average contractual maturity period of securities, years, unrealized loss position | 21 |  | 20 |
Fair value | 2,387 |  | 6,954 |
Total, Unrealized losses | 478 |  | 804 |
Aggregate Unrealized Losses [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
12 months or longer, unrealized losses | 782 |  | 941 |
Non Variable Interest Entities [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Other-than-temporary impairments | 101 |  | 64 | 361
Variable Interest Entities [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrecognized gross losses | 371 |  | 279 |
Other-than-temporary impairments |  |  |  | 106
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 12-month period or longer | 218 |  | 321 |
Asset-Backed Securities [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Percentage of investments rated investment grade | 54.00% |  |  |
Investment grade rated with AAA | 12.00% |  |  |
Fair value | 639 |  |  |
Total, Unrealized losses | 215 |  |  |
Securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 258 |  |  |
Securities rated below investment grade percentage without giving effect to the benefit of guarantees provided by financial guarantors | 40.00% |  |  |
Asset-Backed Securities [Member] | MBIA Corp. [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value | 338 | [1] |  |
Total, Unrealized losses | 78 | [1] |  |
Benefit of Guarantees Provided | 338 |  |  |
Mortgage-Backed Securities [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Percentage of investments rated investment grade | 65.00% |  |  |
Investment grade rated with AAA | 23.00% |  |  |
Fair value | 401 |  |  |
Total, Unrealized losses | 119 |  |  |
Securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 262 |  |  |
Securities rated below investment grade percentage without giving effect to the benefit of guarantees provided by financial guarantors | 65.00% |  |  |
Mortgage-Backed Securities [Member] | MBIA Corp. [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value | 18 | [1] |  |
Total, Unrealized losses | 5 | [1] |  |
Benefit of Guarantees Provided | 18 |  |  |
Corporate Obligations [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Percentage of investments rated investment grade | 80.00% |  |  |
Investment grade rated with AAA | 10.00% |  |  |
Fair value | 717 |  |  |
Total, Unrealized losses | 106 |  |  |
Securities rated below investment grade without giving effect to the benefit of guarantees provided by financial guarantors | 33 |  |  |
Securities rated below investment grade percentage without giving effect to the benefit of guarantees provided by financial guarantors | 5.00% |  |  |
Corporate Obligations [Member] | MBIA Corp. [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value | 97 | [1] |  |
Total, Unrealized losses | 17 | [1] |  |
Securities Pledged as Collateral [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Money market securities pledged as collateral under investment agreements | 224 |  | 113 |
3rd Party Guarantors [Member] | Asset-Backed Securities [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Benefit of Guarantees Provided | 111 |  |  |
3rd Party Guarantors [Member] | Mortgage-Backed Securities [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Benefit of Guarantees Provided | 239 |  |  |
3rd Party Guarantors [Member] | Corporate Obligations [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Benefit of Guarantees Provided | 74 |  |  |
National [Member] | Corporate Obligations [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Benefit of Guarantees Provided | 97 |  |  |
Asset/Liability Products [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Other-than-temporary impairments | 31 |  | 59 | 352
Asset/Liability Products [Member] | Asset-Backed Securities [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value | 397 |  |  |
Total, Unrealized losses | $ 120 |  |  |
[1] | Includes investments insured by MBIA Corp. and National.

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