| **Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions** | Dec. 31, 2015 | Dec. 31, 2014 |
|-----------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | $ 41,469      | $ 42,757      |
| Fair value of liabilities, measured on a recurring basis                                                              | (5)           | 3             |
| Corporate and other bonds [Member]                                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 17,760        | 18,889        |
| States, municipalities and political subdivisions [Member]                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 13,174        | 12,740        |
| Residential mortgage-backed [Member]                                                                                  |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 5,072         | 5,233         |
| Commercial mortgage-backed [Member]                                                                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 2,197         | 2,144         |
| Other asset-backed [Member]                                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 921           | 1,235         |
| Total asset-backed [Member]                                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 8,190         | 8,612         |
| U.S. Treasury and obligations of government-sponsored enterprises [Member]                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 67            | 31            |
| Foreign Government Debt Securities [Member]                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 346           | 454           |
| Redeemable preferred stock [Member]                                                                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 35            | 42            |
| Fixed maturity securities [Member]                                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 39,572        | 40,768        |
| Equity securities [Member]                                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 197           | 222           |
| Other invested assets [Member]                                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 44            | 41            |
| Short term investments [Member]                                                                                       |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 1,582         | 1,644         |
| Life settlement contracts, included in Other assets [Member]                                                          |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 74            | 82            |
| Embedded Derivative Financial Instruments [Member]                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of liabilities, measured on a recurring basis                                                              | (5)           | 3             |
| Level 1 [Member]                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 726           | 957           |
| Fair value of liabilities, measured on a recurring basis                                                              | 0             | 0             |
| Level 1 [Member] | Corporate and other bonds [Member]                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 32            |
| Level 1 [Member] | States, municipalities and political subdivisions [Member]                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 1 [Member] | Residential mortgage-backed [Member]                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 1 [Member] | Commercial mortgage-backed [Member]                                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 1 [Member] | Other asset-backed [Member]                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 1 [Member] | Total asset-backed [Member]                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 1 [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 66            | 28            |
| Level 1 [Member] | Foreign Government Debt Securities [Member]                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 41            |
| Level 1 [Member] | Redeemable preferred stock [Member]                                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 35            | 30            |
| Level 1 [Member] | Fixed maturity securities [Member]                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 101           | 131           |
| Level 1 [Member] | Equity securities [Member]                                                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 177           | 145           |
| Level 1 [Member] | Other invested assets [Member]                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 1 [Member] | Short term investments [Member]                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 448           | 681           |
| Level 1 [Member] | Life settlement contracts, included in Other assets [Member]                                       |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 1 [Member] | Embedded Derivative Financial Instruments [Member]                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of liabilities, measured on a recurring basis                                                              | 0             | 0             |
| Level 2 [Member]                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 40,270        | 40,519        |
| Fair value of liabilities, measured on a recurring basis                                                              | (5)           | 3             |
| Level 2 [Member] | Corporate and other bonds [Member]                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 17,592        | 18,695        |
| Level 2 [Member] | States, municipalities and political subdivisions [Member]                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 13,172        | 12,646        |
| Level 2 [Member] | Residential mortgage-backed [Member]                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 4,938         | 5,044         |
| Level 2 [Member] | Commercial mortgage-backed [Member]                                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 2,175         | 2,061         |
| Level 2 [Member] | Other asset-backed [Member]                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 868           | 580           |
| Level 2 [Member] | Total asset-backed [Member]                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 7,981         | 7,685         |
| Level 2 [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 1             | 3             |
| Level 2 [Member] | Foreign Government Debt Securities [Member]                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 346           | 413           |
| Level 2 [Member] | Redeemable preferred stock [Member]                                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 12            |
| Level 2 [Member] | Fixed maturity securities [Member]                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 39,092        | 39,454        |
| Level 2 [Member] | Equity securities [Member]                                                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 61            |
| Level 2 [Member] | Other invested assets [Member]                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 44            | 41            |
| Level 2 [Member] | Short term investments [Member]                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 1,134         | 963           |
| Level 2 [Member] | Life settlement contracts, included in Other assets [Member]                                       |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 2 [Member] | Embedded Derivative Financial Instruments [Member]                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of liabilities, measured on a recurring basis                                                              | (5)           | 3             |
| Level 3 [Member]                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 473           | 1,281         |
| Fair value of liabilities, measured on a recurring basis                                                              | 0             | 0             |
| Level 3 [Member] | Corporate and other bonds [Member]                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 168           | 162           |
| Level 3 [Member] | States, municipalities and political subdivisions [Member]                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 2             | 94            |
| Level 3 [Member] | Residential mortgage-backed [Member]                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 134           | 189           |
| Level 3 [Member] | Commercial mortgage-backed [Member]                                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 22            | 83            |
| Level 3 [Member] | Other asset-backed [Member]                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 53            | 655           |
| Level 3 [Member] | Total asset-backed [Member]                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 209           | 927           |
| Level 3 [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 3 [Member] | Foreign Government Debt Securities [Member]                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 3 [Member] | Redeemable preferred stock [Member]                                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 3 [Member] | Fixed maturity securities [Member]                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 379           | 1,183         |
| Level 3 [Member] | Equity securities [Member]                                                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 20            | 16            |
| Level 3 [Member] | Other invested assets [Member]                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 3 [Member] | Short term investments [Member]                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 0             | 0             |
| Level 3 [Member] | Life settlement contracts, included in Other assets [Member]                                       |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of assets, measured on a recurring basis                                                                   | 74            | 82            |
| Level 3 [Member] | Embedded Derivative Financial Instruments [Member]                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                      |          |          |
| Fair value of liabilities, measured on a recurring basis                                                              | $ 0           | $ 0           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.
+ References
No definition available.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
No definition available.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Aggregation of the liabilities reported on the balance sheet measured at fair value on a recurring basis by the entity.
+ References
No definition available.
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