| **Investments (Securities in a gross unrealized loss position) (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | $ 9,256         | $ 1,819 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 388             | 27 |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 544             | 866 |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 144             | 128 |
| Estimated Fair Value, Total                                                                                               | 9,800           | 2,685 |
| Gross Unrealized Losses, Total                                                                                            | 532             | 155 |
| Corporate and other bonds [Member]                                                                                        |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 3,592           | 846 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 129             | 13 |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 72              | 108 |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 6               | 8 |
| Estimated Fair Value, Total                                                                                               | 3,664           | 954 |
| Gross Unrealized Losses, Total                                                                                            | 135             | 21 |
| States, municipalities and political subdivisions [Member]                                                                |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 3,251           | 254 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 197             | 5 |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 129             | 165 |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 75              | 39 |
| Estimated Fair Value, Total                                                                                               | 3,380           | 419 |
| Gross Unrealized Losses, Total                                                                                            | 272             | 44 |
| Residential mortgage-backed [Member]                                                                                      |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 1,293           | 583 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 29              | 5 |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 343             | 452 |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 63              | 66 |
| Estimated Fair Value, Total                                                                                               | 1,636           | 1,035 |
| Gross Unrealized Losses, Total                                                                                            | 92              | 71 |
| Commercial mortgage-backed [Member]                                                                                       |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 640             | 85 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 22              | 2 |
| Estimated Fair Value, 12 Months or Longer                                                                                 |       | 141 |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |       | 15 |
| Estimated Fair Value, Total                                                                                               | 640             | 226 |
| Gross Unrealized Losses, Total                                                                                            | 22              | 17 |
| Other asset-backed [Member]                                                                                               |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 269             |   |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 3               |   |
| Estimated Fair Value, 12 Months or Longer                                                                                 |       |   |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |       |   |
| Estimated Fair Value, Total                                                                                               | 269             |   |
| Gross Unrealized Losses, Total                                                                                            | 3               |   |
| Total asset-backed [Member]                                                                                               |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 2,202           | 668 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 54              | 7 |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 343             | 593 |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 63              | 81 |
| Estimated Fair Value, Total                                                                                               | 2,545           | 1,261 |
| Gross Unrealized Losses, Total                                                                                            | 117             | 88 |
| U.S. Treasury and obligations of government-sponsored enterprises [Member]                                                |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 13              | 23 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 1               | 1 |
| Estimated Fair Value, 12 Months or Longer                                                                                 |       |    |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |       |    |
| Estimated Fair Value, Total                                                                                               | 13              | 23 |
| Gross Unrealized Losses, Total                                                                                            | 1               | 1 |
| Foreign Government Debt Securities [Member]                                                                               |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 111             |   |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 3               |   |
| Estimated Fair Value, 12 Months or Longer                                                                                 |       |   |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |       |   |
| Estimated Fair Value, Total                                                                                               | 111             |   |
| Gross Unrealized Losses, Total                                                                                            | 3               |   |
| Redeemable preferred stock [Member]                                                                                       |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 |            | 28 |
| 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                                                                                               |            | 28 |
| Gross Unrealized Losses, Total                                                                                            |            | 1 |
| Total fixed maturity securities available-for-sale [Member]                                                               |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 9,169           | 1,819 |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 384             | 27 |
| Estimated Fair Value, 12 Months or Longer                                                                                 | 544             | 866 |
| Gross Unrealized Losses, 12 Months or Longer                                                                              | 144             | 128 |
| Estimated Fair Value, Total                                                                                               | 9,713           | 2,685 |
| Gross Unrealized Losses, Total                                                                                            | 528             | 155 |
| Preferred stock [Member]                                                                                                  |            |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                |            |   |
| Estimated Fair Value, Less than 12 Months                                                                                 | 87              |   |
| Gross Unrealized Losses, Less than 12 Months                                                                              | 4               |   |
| Estimated Fair Value, 12 Months or Longer                                                                                 |       |   |
| Gross Unrealized Losses, 12 Months or Longer                                                                              |       |   |
| Estimated Fair Value, Total                                                                                               | 87              |   |
| Gross Unrealized Losses, Total                                                                                            | $ 4             |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrealized loss on securities classified as available-for-sale.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
Amount of unrealized loss on investments in available-for-sale securities that have been in a 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 less than twelve months.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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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