| **Employee Retirement Benefits (Fair Value Hierarchy Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions** | Dec. 31, 2017 | Dec. 31, 2016 |
|-------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | $ 10,699      | $ 10,085      |
| Available for sale securities, equity securities                                                                                                | 6,249         | 5,334         |
| Fixed Maturities                                                                                                                                |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 65            | 51            |
| Fixed Maturities | States, Municipalities and Political Subdivisions                                                                            |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 31            | 31            |
| Fixed Maturities | Corporate Fixed Maturities                                                                                                   |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 34            | 20            |
| Equity Securities | Common Stock                                                                                                                |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, equity securities                                                                                                | 262           | 253           |
| Debt And Equity Securities                                                                                                                      |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, equity securities                                                                                                | 327           | 304           |
| Level 1 | Fixed Maturities                                                                                                                      |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 0             | 0             |
| Level 1 | Fixed Maturities | States, Municipalities and Political Subdivisions                                                                  |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 0             | 0             |
| Level 1 | Fixed Maturities | Corporate Fixed Maturities                                                                                         |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 0             | 0             |
| Level 1 | Equity Securities | Common Stock                                                                                                      |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, equity securities                                                                                                | 262           | 253           |
| Level 1 | Debt And Equity Securities                                                                                                            |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, equity securities                                                                                                | 262           | 253           |
| Level 2 | Fixed Maturities                                                                                                                      |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 65            | 51            |
| Level 2 | Fixed Maturities | States, Municipalities and Political Subdivisions                                                                  |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 31            | 31            |
| Level 2 | Fixed Maturities | Corporate Fixed Maturities                                                                                         |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 34            | 20            |
| Level 2 | Equity Securities | Common Stock                                                                                                      |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, equity securities                                                                                                | 0             | 0             |
| Level 2 | Debt And Equity Securities                                                                                                            |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 65            | 51            |
| Level 3 | Fixed Maturities                                                                                                                      |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 0             | 0             |
| Level 3 | Fixed Maturities | States, Municipalities and Political Subdivisions                                                                  |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 0             | 0             |
| Level 3 | Fixed Maturities | Corporate Fixed Maturities                                                                                         |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, debt securities                                                                                                  | 0             | 0             |
| Level 3 | Equity Securities | Common Stock                                                                                                      |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, equity securities                                                                                                | 0             | 0             |
| Level 3 | Debt And Equity Securities                                                                                                            |          |          |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                       |          |          |
| Available for sale securities, equity securities                                                                                                | $ 0           | $ 0           |

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