| **Reinsurance Reinsurance (Written Consolidated Property Casualty Insurance Premiums On Assumed and Ceded Business) (Details) - USD ($) $ in Millions** | 12 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**                                                                                               |            |   |   |
| Direct premiums earned                                                                                                                                  | $ 5,681         | $ 5,251 | $ 5,052 |
| Assumed premiums earned                                                                                                                                 | 199             | 149 | 132 |
| Ceded premiums earned                                                                                                                                   | 276             | 230 | 230 |
| Incurred loss and loss expenses                                                                                                                         | 3,638           | 3,490 | 3,390 |
| Consolidated Property and Casualty Insurance Entity                                                                                                     |            |   |   |
| **SEC Schedule, 12-17, Insurance Companies, Reinsurance**                                                                                               |            |   |   |
| Direct premiums written                                                                                                                                 | 5,477           | 5,018 | 4,854 |
| Assumed premiums written                                                                                                                                | 244             | 173 | 125 |
| Ceded premiums written                                                                                                                                  | (205)           | (161) | (139) |
| Net written premiums                                                                                                                                    | 5,516           | 5,030 | 4,840 |
| Direct premiums earned                                                                                                                                  | 5,340           | 4,931 | 4,752 |
| Assumed premiums earned                                                                                                                                 | 199             | 149 | 132 |
| Ceded premiums earned                                                                                                                                   | (205)           | (160) | (162) |
| Earned premiums                                                                                                                                         | 5,334           | 4,920 | 4,722 |
| Direct incurred loss and loss expenses                                                                                                                  | 3,402           | 3,188 | 2,961 |
| Assumed incurred loss and loss expenses                                                                                                                 | 117             | 125 | 113 |
| Ceded incurred loss and loss expenses                                                                                                                   | (167)           | (90) | 64 |
| Incurred loss and loss expenses                                                                                                                         | $ 3,352         | $ 3,223 | $ 3,138 |

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