| **Investments (Contractual Maturity Dates For Fixed-Maturity And Short-Term Investments) (Details) - USD ($) $ in Millions** | Dec. 31, 2019 | Dec. 31, 2018 |
|------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Amortized cost**                                                                                                           |          |          |
| Due in one year or less                                                                                                      | $ 455         |          |
| Due after one year through five years                                                                                        | 3,180         |          |
| Due after five years through ten years                                                                                       | 3,792         |          |
| Due after ten years                                                                                                          | 3,681         |          |
| Total                                                                                                                        | 11,108        | $ 10,643      |
| **Fair value**                                                                                                               |          |          |
| Due in one year or less                                                                                                      | 459           |          |
| Due after one year through five years                                                                                        | 3,302         |          |
| Due after five years through ten years                                                                                       | 4,011         |          |
| Due after ten years                                                                                                          | 3,926         |          |
| Total                                                                                                                        | $ 11,698      | $ 10,689      |
| **% of fair value**                                                                                                          |          |          |
| Due in one year or less                                                                                                      | 3.90%         |          |
| Due after one year through five years                                                                                        | 28.20%        |          |
| Due after five years through ten years                                                                                       | 34.30%        |          |
| Due after ten years                                                                                                          | 33.60%        |          |
| Total                                                                                                                        | 100.00%       |          |

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