| **Reinsurance (Components of Earned Premiums) (Details) - USD ($) $ in Millions**    | 12 Months Ended |
|--------------------------------------------------------------------------------------|-----------------|
||
| **Premiums Earned, Net [Abstract]**                                                  |            |   |   |
| Direct                                                                               | $ 13,524        | $ 12,997 | $ 12,001 |
| Assumed                                                                              | 277             | 288 | 288 |
| Ceded                                                                                | 5,134           | 5,110 | 4,640 |
| Net                                                                                  | 8,667           | 8,175 | 7,649 |
| Property and casualty                                                                |            |   |   |
| **Premiums Earned, Net [Abstract]**                                                  |            |   |   |
| Direct                                                                               | 13,097          | 12,554 | 11,547 |
| Assumed                                                                              | 231             | 240 | 238 |
| Ceded                                                                                | 5,134           | 5,110 | 4,640 |
| Net                                                                                  | 8,194           | 7,684 | 7,145 |
| Long term care                                                                       |            |   |   |
| **Premiums Earned, Net [Abstract]**                                                  |            |   |   |
| Direct                                                                               | 427             | 443 | 454 |
| Assumed                                                                              | 46              | 48 | 50 |
| Ceded                                                                                | 0               | 0 | 0 |
| Net                                                                                  | $ 473           | $ 491 | $ 504 |
| Percentage of assumed premiums earned to net premiums earned                         |            |   |   |
| **Premiums Earned, Net [Abstract]**                                                  |            |   |   |
| Assumed/ Net %                                                                       | 3.20%           | 3.50% | 3.80% |
| Percentage of assumed premiums earned to net premiums earned | Property and casualty |            |   |   |
| **Premiums Earned, Net [Abstract]**                                                  |            |   |   |
| Assumed/ Net %                                                                       | 2.80%           | 3.10% | 3.30% |
| Percentage of assumed premiums earned to net premiums earned | Long term care        |            |   |   |
| **Premiums Earned, Net [Abstract]**                                                  |            |   |   |
| Assumed/ Net %                                                                       | 9.70%           | 9.80% | 9.90% |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of earned premiums assumed from other entities.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of earned premiums ceded to other entities.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of assumed premium earned to premium earned after effects of reinsurance, as disclosed in supplementary reinsurance information.
+ References
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| X                                                                                                                                                                                                                                                   |
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| - References
No definition available.
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