| **Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions**        | Sep. 30, 2015 | Dec. 31, 2014 |
|-----------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | $ 5,570       | $ 2,855       |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 201           | 70            |
| Estimated Fair Value, 12 Months or Longer                                                                 | 637           | 707           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 52            | 29            |
| Estimated Fair Value, Total                                                                               | 6,207         | 3,562         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 253           | 99            |
| Corporate and other bonds [Member]                                                                        |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 3,744         | 1,330         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 177           | 46            |
| Estimated Fair Value, 12 Months or Longer                                                                 | 188           | 277           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 30            | 15            |
| Estimated Fair Value, Total                                                                               | 3,932         | 1,607         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 207           | 61            |
| States, municipalities and political subdivisions [Member]                                                |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 655           | 335           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 11            | 5             |
| Estimated Fair Value, 12 Months or Longer                                                                 | 131           | 127           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 6             | 3             |
| Estimated Fair Value, Total                                                                               | 786           | 462           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 17            | 8             |
| Residential mortgage-backed [Member]                                                                      |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 308           | 293           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 3             | 5             |
| Estimated Fair Value, 12 Months or Longer                                                                 | 211           | 189           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 10            | 8             |
| Estimated Fair Value, Total                                                                               | 519           | 482           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 13            | 13            |
| Commercial mortgage-backed [Member]                                                                       |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 479           | 264           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 6             | 2             |
| Estimated Fair Value, 12 Months or Longer                                                                 | 81            | 99            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 3             | 3             |
| Estimated Fair Value, Total                                                                               | 560           | 363           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 9             | 5             |
| Other asset-backed [Member]                                                                               |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 354           | 607           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 4             | 10            |
| Estimated Fair Value, 12 Months or Longer                                                                 | 9             | 7             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0             | 0             |
| Estimated Fair Value, Total                                                                               | 363           | 614           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 4             | 10            |
| Total asset-backed [Member]                                                                               |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 1,141         | 1,164         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 13            | 17            |
| Estimated Fair Value, 12 Months or Longer                                                                 | 301           | 295           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 13            | 11            |
| Estimated Fair Value, Total                                                                               | 1,442         | 1,459         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 26            | 28            |
| 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                                                                 | 1             | 3             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0             | 0             |
| Estimated Fair Value, 12 Months or Longer                                                                 | 0             | 4             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0             | 0             |
| Estimated Fair Value, Total                                                                               | 1             | 7             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 0             | 0             |
| Foreign Government Debt Securities [Member]                                                               |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 23            | 3             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0             | 0             |
| Estimated Fair Value, 12 Months or Longer                                                                 | 3             | 3             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 1             | 0             |
| Estimated Fair Value, Total                                                                               | 26            | 6             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 1             | 0             |
| Redeemable preferred stock [Member]                                                                       |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 3             | 3             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0             | 0             |
| Estimated Fair Value, 12 Months or Longer                                                                 | 0             | 0             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0             | 0             |
| Estimated Fair Value, Total                                                                               | 3             | 3             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 0             | 0             |
| Total fixed maturity securities available-for-sale [Member]                                               |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 5,567         | 2,838         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 201           | 68            |
| Estimated Fair Value, 12 Months or Longer                                                                 | 623           | 706           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 50            | 29            |
| Estimated Fair Value, Total                                                                               | 6,190         | 3,544         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | 251           | 97            |
| Preferred stock [Member]                                                                                  |          |          |
| **Schedule of Available-for-sale Securities [Line Items]**                                                |          |          |
| Estimated Fair Value, Less than 12 Months                                                                 | 3             | 17            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0             | 2             |
| Estimated Fair Value, 12 Months or Longer                                                                 | 14            | 1             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 2             | 0             |
| Estimated Fair Value, Total                                                                               | 17            | 18            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                      | $ 2           | $ 2           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.
+ 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
Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous 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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| - 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.
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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No definition available.
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