| **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, 2017 | Dec. 31, 2016 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | $ 809         | $ 2,079       |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 20            | 71            |
| 12 months or more fair value                                                                                                                                                            | 682           | 191           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 18            | 11            |
| Total fair value                                                                                                                                                                        | 1,491         | 2,270         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 38            | 82            |
| Fixed Maturities                                                                                                                                                                        |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 580           | 1,972         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 6             | 62            |
| 12 months or more fair value                                                                                                                                                            | 682           | 191           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 18            | 11            |
| Total fair value                                                                                                                                                                        | 1,262         | 2,163         |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 24            | 73            |
| Fixed Maturities | Corporate Securities                                                                                                                                                 |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 330           | 733           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 4             | 15            |
| 12 months or more fair value                                                                                                                                                            | 252           | 189           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 9             | 11            |
| Total fair value                                                                                                                                                                        | 582           | 922           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 13            | 26            |
| Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                                                    |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 88            | 989           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 1             | 42            |
| 12 months or more fair value                                                                                                                                                            | 264           | 0             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 5             | 0             |
| Total fair value                                                                                                                                                                        | 352           | 989           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 6             | 42            |
| Fixed Maturities | Commercial Mortgage Backed Securities                                                                                                                                |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 33            | 89            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 0             | 2             |
| 12 months or more fair value                                                                                                                                                            | 36            | 2             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 1             | 0             |
| Total fair value                                                                                                                                                                        | 69            | 91            |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 1             | 2             |
| Fixed Maturities | Government-Sponsored Enterprises                                                                                                                                     |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 96            | 155           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 1             | 3             |
| 12 months or more fair value                                                                                                                                                            | 124           | 0             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 3             | 0             |
| Total fair value                                                                                                                                                                        | 220           | 155           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 4             | 3             |
| Fixed Maturities | Foreign government                                                                                                                                                   |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 10            |          |
| 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                                                                                                                                                                        | 10            |          |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 0             |          |
| Fixed Maturities | United States Government                                                                                                                                             |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 23            | 6             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 0             | 0             |
| 12 months or more fair value                                                                                                                                                            | 6             | 0             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss                                                                               | 0             | 0             |
| Total fair value                                                                                                                                                                        | 29            | 6             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 0             | 0             |
| Equity Securities                                                                                                                                                                       |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 229           | 107           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 14            | 9             |
| 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                                                                                                                                                                        | 229           | 107           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | 14            | 9             |
| Equity Securities | Common Equities                                                                                                                                                     |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          | 229           | 103           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss                                                                               | 14            | 9             |
| 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                                                                                                                                                                        | 229           | 103           |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    | $ 14          | 9             |
| Equity Securities | Nonredeemable Preferred Equities                                                                                                                                    |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                               |          |          |
| Less than 12 months fair value                                                                                                                                                          |          | 4             |
| 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                                                                                                                                                                        |          | 4             |
| Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss                                                                                                    |          | $ 0           |

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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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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.
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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.
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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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