| **Investments (Securities in a gross unrealized loss position) (Details) (USD $)In Millions, unless otherwise specified** | Sep. 30, 2012 | Dec. 31, 2011 |
|---------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Total available-for-sale securities [Member]                                                                              |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | $ 1,241       | $ 4,275       |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 26            | 211           |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 1,149         | 1,923         |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 159           | 330           |
| Estimated Fair Value, Total                                                                                               | 2,390         | 6,198         |
| Gross Unrealized Losses, Total                                                                                            | 185           | 541           |
| Corporate and other bonds [Member]                                                                                        |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 600           | 2,552         |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 18            | 126           |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 210           | 159           |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 14            | 28            |
| Estimated Fair Value, Total                                                                                               | 810           | 2,711         |
| Gross Unrealized Losses, Total                                                                                            | 32            | 154           |
| States, municipalities and political subdivisions [Member]                                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 84            | 67            |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 1             | 1             |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 227           | 721           |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 52            | 135           |
| Estimated Fair Value, Total                                                                                               | 311           | 788           |
| Gross Unrealized Losses, Total                                                                                            | 53            | 136           |
| Residential mortgage-backed [Member]                                                                                      |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 327           | 719           |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 3             | 36            |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 580           | 874           |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 78            | 147           |
| Estimated Fair Value, Total                                                                                               | 907           | 1,593         |
| Gross Unrealized Losses, Total                                                                                            | 81            | 183           |
| Commercial mortgage-backed [Member]                                                                                       |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 142           | 431           |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 2             | 39            |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 132           | 169           |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 15            | 20            |
| Estimated Fair Value, Total                                                                                               | 274           | 600           |
| Gross Unrealized Losses, Total                                                                                            | 17            | 59            |
| Other asset-backed [Member]                                                                                               |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 66            | 389           |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 1             | 4             |
| Estimated Fair Value, 12 Months or Longer                                                                                 |     |     |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |     |     |
| Estimated Fair Value, Total                                                                                               | 66            | 389           |
| Gross Unrealized Losses, Total                                                                                            | 1             | 4             |
| Total asset-backed [Member]                                                                                               |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 535           | 1,539         |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 6             | 79            |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 712           | 1,043         |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 93            | 167           |
| Estimated Fair Value, Total                                                                                               | 1,247         | 2,582         |
| Gross Unrealized Losses, Total                                                                                            | 99            | 246           |
| US Treasury and Government [Member]                                                                                       |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 | 22            |          |
| 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                                                                                               | 22            |          |
| Gross Unrealized Losses, Total                                                                                            | 1             |          |
| Total fixed maturity securities available-for-sale [Member]                                                               |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 |          | 4,158         |
| Gross Unrealized Losses, Less than 12 Months                                                                              |          | 206           |
| Estimated Fair Value, 12 Months or Longer                                                                                 |          | 1,923         |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |          | 330           |
| Estimated Fair Value, Total                                                                                               |          | 6,081         |
| Gross Unrealized Losses, Total                                                                                            |          | 536           |
| Preferred stock [Member]                                                                                                  |          |          |
| Estimated Fair Value, Less than 12 Months                                                                                 |          | 117           |
| Gross Unrealized Losses, Less than 12 Months                                                                              |          | 5             |
| Estimated Fair Value, 12 Months or Longer                                                                                 |          |     |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |          |     |
| Estimated Fair Value, Total                                                                                               |          | 117           |
| Gross Unrealized Losses, Total                                                                                            |          | $ 5           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
+ References
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
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27337-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 03-1 -Paragraph 21 -Subparagraph a(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 17 -Subparagraph a(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563
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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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