| **Investments (Fair Values And Unrealized Losses By Investment Category And By The Duration Of The Securities' Continuous Unrealized Loss Position) (Details) - USD ($) $ in Millions** | Dec. 31, 2016 | Dec. 31, 2015 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | $ 2,079       | $ 1,654       |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 71            | 119           |
| 12 months or more fair value                                                                                                                                                            | 191           | 284           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 11            | 37            |
| Total fair value                                                                                                                                                                        | 2,270         | 1,938         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 82            | 156           |
| Fixed Maturities                                                                                                                                                                        |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 1,972         | 1,349         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 62            | 68            |
| 12 months or more fair value                                                                                                                                                            | 191           | 284           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 11            | 37            |
| Total fair value                                                                                                                                                                        | 2,163         | 1,633         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 73            | 105           |
| Fixed Maturities | Corporate Securities                                                                                                                                                 |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 733           | 1,099         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 15            | 63            |
| 12 months or more fair value                                                                                                                                                            | 189           | 133           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 11            | 33            |
| Total fair value                                                                                                                                                                        | 922           | 1,232         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 26            | 96            |
| Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                                                    |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 989           | 47            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 42            | 1             |
| 12 months or more fair value                                                                                                                                                            | 0             | 22            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             | 0             |
| Total fair value                                                                                                                                                                        | 989           | 69            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 42            | 1             |
| Fixed Maturities | Commercial Mortgage Backed Securities                                                                                                                                |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 89            | 103           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 2             | 2             |
| 12 months or more fair value                                                                                                                                                            | 2             | 2             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             | 0             |
| Total fair value                                                                                                                                                                        | 91            | 105           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 2             | 2             |
| Fixed Maturities | Government-Sponsored Enterprises                                                                                                                                     |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 155           | 100           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 3             | 2             |
| 12 months or more fair value                                                                                                                                                            | 0             | 127           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             | 4             |
| Total fair value                                                                                                                                                                        | 155           | 227           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 3             | 6             |
| Fixed Maturities | United States Government                                                                                                                                             |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 6             |          |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 0             |          |
| 12 months or more fair value                                                                                                                                                            | 0             |          |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             |          |
| Total fair value                                                                                                                                                                        | 6             |          |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 0             |          |
| Equity Securities                                                                                                                                                                       |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 107           | 305           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 9             | 51            |
| 12 months or more fair value                                                                                                                                                            | 0             | 0             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             | 0             |
| Total fair value                                                                                                                                                                        | 107           | 305           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 9             | 51            |
| Equity Securities | Common Equities                                                                                                                                                     |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 103           | 270           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 9             | 51            |
| 12 months or more fair value                                                                                                                                                            | 0             | 0             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             | 0             |
| Total fair value                                                                                                                                                                        | 103           | 270           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 9             | 51            |
| Equity Securities | Nonredeemable Preferred Equities                                                                                                                                    |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 4             | 35            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 0             | 0             |
| 12 months or more fair value                                                                                                                                                            | 0             | 0             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             | 0             |
| Total fair value                                                                                                                                                                        | 4             | 35            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | $ 0           | $ 0           |

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Investments, Unrealized Loss Position [Line Items]
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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 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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