| **Property Casualty Loss And Loss Expenses (Claims Development - Personal Auto) (Details) reported_claim in Thousands, $ in Millions** | Dec. 31, 2018 USD ($) reported_claim | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) |
|----------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------|-----------------------|-----------------------|-----------------------|-----------------------|
| **Claims Development [Line Items]**                                                                                                    |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                           | $ 2,588                              |                  |                  |                  |                  |
| Liabilities for loss and ALAE, net of reinsurance                                                                                      | 5,366                                |                  |                  |                  |                  |
| Personal Auto | Personal Insurance                                                                                                     |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                    |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                           | 1,889                                |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                    | 1,603                                |                  |                  |                  |                  |
| All outstanding liabilities before, net of reinsurance                                                                                 | 4                                    |                  |                  |                  |                  |
| Liabilities for loss and ALAE, net of reinsurance                                                                                      | 290                                  |                  |                  |                  |                  |
| 2014 | Personal Auto | Personal Insurance                                                                                              |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                    |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                           | 325                                  | $ 324                 | $ 325                 | $ 317                 | $ 317                 |
| Total of incurred but not reported liabilities plus expected development on reported losses                                            | $ 0                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                  | 105                                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                    | $ 320                                | 313                   | 298                   | 267                   | $ 210                 |
| 2015 | Personal Auto | Personal Insurance                                                                                              |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                    |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                           | 360                                  | 356                   | 356                   | 343                   |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                            | $ 0                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                  | 108                                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                    | $ 346                                | 325                   | 292                   | $ 229                 |                  |
| 2016 | Personal Auto | Personal Insurance                                                                                              |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                    |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                           | 386                                  | 384                   | 383                   |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                            | $ 3                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                  | 110                                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                    | $ 351                                | 316                   | $ 243                 |                  |                  |
| 2017 | Personal Auto | Personal Insurance                                                                                              |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                    |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                           | 394                                  | 412                   |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                            | $ 14                                 |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                  | 109                                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                    | $ 324                                | $ 256                 |                  |                  |                  |
| 2018 | Personal Auto | Personal Insurance                                                                                              |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                    |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                           | 424                                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                            | $ 64                                 |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                  | 104                                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                    | $ 262                                |                  |                  |                  |                  |

| 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.
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No definition available.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after reinsurance, of paid claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense.
+ References
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| - Definition
Undiscounted amount, after reinsurance, of incurred-but-not-reported (IBNR) liabilities plus expected development on reported claims, for claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense.
+ References
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| - Definition
Undiscounted amount, after reinsurance, of incurred claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense.
+ References
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| - Definition
Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts for accident years not separately presented in claim development information. Excludes unallocated claim adjustment expense.
+ References
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| - Definition
Number of reported claims for short-duration insurance contracts.
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