| **Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) - USD ($) $ in Millions** | Dec. 31, 2018 | Dec. 31, 2017 |
|---------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | $ 2,025       | $ 2,261       |
| Level 1, 2 and 3                                                                                              |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 1,236         | 1,357         |
| Total limited partnerships measured at net asset value                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 789           | 904           |
| Corporate and other bonds                                                                                     |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 482           | 532           |
| Corporate and other bonds | Level 1                                                                           |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Corporate and other bonds | Level 2                                                                           |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 472           | 522           |
| Corporate and other bonds | Level 3                                                                           |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 10            | 10            |
| States, municipalities and political subdivisions                                                             |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 58            | 62            |
| States, municipalities and political subdivisions | Level 1                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| States, municipalities and political subdivisions | Level 2                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 58            | 62            |
| States, municipalities and political subdivisions | Level 3                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Asset-backed                                                                                                  |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 165           | 180           |
| Asset-backed | Level 1                                                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Asset-backed | Level 2                                                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 165           | 180           |
| Asset-backed | Level 3                                                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Total fixed maturity securities trading                                                                       |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 705           | 774           |
| Total fixed maturity securities trading | Level 1                                                             |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Total fixed maturity securities trading | Level 2                                                             |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 695           | 764           |
| Total fixed maturity securities trading | Level 3                                                             |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 10            | 10            |
| Equity securities                                                                                             |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 441           |          |
| Equity securities | Level 1                                                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 331           |          |
| Equity securities | Level 2                                                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 110           |          |
| Equity securities | Level 3                                                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             |          |
| Equity securities                                                                                             |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 527           |
| Equity securities | Level 1                                                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 405           |
| Equity securities | Level 2                                                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 122           |
| Equity securities | Level 3                                                                                   |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 0             |
| Short term investments                                                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 81            | 34            |
| Short term investments | Level 1                                                                              |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 27            | 23            |
| Short term investments | Level 2                                                                              |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 54            | 11            |
| Short term investments | Level 3                                                                              |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Other assets                                                                                                  |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 9             | 9             |
| Other assets | Level 1                                                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Other assets | Level 2                                                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 9             | 9             |
| Other assets | Level 3                                                                                        |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 0             | 0             |
| Cash                                                                                                          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 13            |
| Cash | Level 1                                                                                                |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 13            |
| Cash | Level 2                                                                                                |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 0             |
| Cash | Level 3                                                                                                |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     |          | 0             |
| Total assets measured at fair value | Level 1                                                                 |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 358           | 441           |
| Total assets measured at fair value | Level 2                                                                 |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | 868           | 906           |
| Total assets measured at fair value | Level 3                                                                 |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                              |          |          |
| Fair value of plan assets                                                                                     | $ 10          | $ 10          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.
+ References
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