| **Investments (Securities in a gross unrealized loss position) (Details) (USD $)In Millions, unless otherwise specified** | Dec. 31, 2011 | Dec. 31, 2010 |
|---------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Total available-for-sale securities [Member]                                                                              |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | $ 4,275       | $ 7,327       |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 211           | 260           |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 1,923         | 3,414         |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 330           | 544           |
| Estimated Fair Value, Total                                                                                               | 6,198         | 10,741        |
| Gross Unrealized Losses, Total                                                                                            | 541           | 804           |
| Corporate and other bonds [Member]                                                                                        |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 2,552         | 1,719         |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 126           | 34            |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 159           | 405           |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 28            | 36            |
| Estimated Fair Value, Total                                                                                               | 2,711         | 2,124         |
| Gross Unrealized Losses, Total                                                                                            | 154           | 70            |
| States, municipalities and political subdivisions [Member]                                                                |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 67            | 3,339         |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 1             | 164           |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 721           | 745           |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 135           | 246           |
| Estimated Fair Value, Total                                                                                               | 788           | 4,084         |
| Gross Unrealized Losses, Total                                                                                            | 136           | 410           |
| Residential mortgage-backed [Member]                                                                                      |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 719           | 1,800         |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 36            | 52            |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 874           | 1,801         |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 147           | 213           |
| Estimated Fair Value, Total                                                                                               | 1,593         | 3,601         |
| Gross Unrealized Losses, Total                                                                                            | 183           | 265           |
| Commercial mortgage-backed [Member]                                                                                       |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 431           | 164           |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 39            | 3             |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 169           | 333           |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 20            | 38            |
| Estimated Fair Value, Total                                                                                               | 600           | 497           |
| Gross Unrealized Losses, Total                                                                                            | 59            | 41            |
| Other asset-backed [Member]                                                                                               |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 389           | 122           |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 4             | 1             |
| Estimated Fair Value, 12 Months or Longer                                                                                 |     | 60            |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |     | 7             |
| Estimated Fair Value, Total                                                                                               | 389           | 182           |
| Gross Unrealized Losses, Total                                                                                            | 4             | 8             |
| Total asset-backed [Member]                                                                                               |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 1,539         | 2,086         |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 79            | 56            |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 1,043         | 2,194         |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 167           | 258           |
| Estimated Fair Value, Total                                                                                               | 2,582         | 4,280         |
| Gross Unrealized Losses, Total                                                                                            | 246           | 314           |
| US Treasury and Government [Member]                                                                                       |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 |          | 8             |
| Gross Unrealized Losses, Less than 12 Months                                                                              |          | 1             |
| Estimated Fair Value, 12 Months or Longer                                                                                 |          |     |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |          |     |
| Estimated Fair Value, Total                                                                                               |          | 8             |
| Gross Unrealized Losses, Total                                                                                            |          | 1             |
| Total fixed maturity securities available-for-sale [Member]                                                               |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 4,158         | 7,152         |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 206           | 255           |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 1,923         | 3,344         |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 330           | 540           |
| Estimated Fair Value, Total                                                                                               | 6,081         | 10,496        |
| Gross Unrealized Losses, Total                                                                                            | 536           | 795           |
| Preferred stock [Member]                                                                                                  |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 117           | 175           |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 5             | 5             |
| Estimated Fair Value, 12 Months or Longer                                                                                 |     | 70            |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |     | 4             |
| Estimated Fair Value, Total                                                                                               | 117           | 245           |
| Gross Unrealized Losses, Total                                                                                            | 5             | 9             |
| Total equity securities available-for-sale [Member]                                                                       |          |          |
| **Available-for-sale Securities, Continuous Unrealized Loss Position**                                                    |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 117           | 175           |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 5             | 5             |
| Estimated Fair Value, 12 Months or Longer                                                                                 |     | 70            |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |     | 4             |
| Estimated Fair Value, Total                                                                                               | 117           | 245           |
| Gross Unrealized Losses, Total                                                                                            | $ 5           | $ 9           |

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| - Definition
This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for those securities which are categorized neither as held-to-maturity nor trading securities.
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No definition available.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the excess of amortized cost basis over fair value of securities in a loss position and which are categorized neither as held-to-maturity nor trading securities.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for those securities which are categorized neither as held-to-maturity nor trading securities.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.
+ References
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