| **Property Casualty Loss And Loss Expenses (Claims Development - Commercial Property) (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                                |                  |                  |                  |                  |
| Commercial Property Line | Commercial Insurance                                                                                              |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                          |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                 | 2,588                                |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                          | 2,287                                |                  |                  |                  |                  |
| All outstanding liabilities before, net of reinsurance                                                                                       | 13                                   |                  |                  |                  |                  |
| Liabilities for loss and ALAE, net of reinsurance                                                                                            | 314                                  |                  |                  |                  |                  |
| 2014 | Commercial Property Line | Commercial Insurance                                                                                       |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                          |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                 | 442                                  | $ 442                 | $ 441                 | $ 444                 | $ 452                 |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                  | $ 1                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                        | 17                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                          | $ 440                                | 437                   | 432                   | 412                   | $ 297                 |
| 2015 | Commercial Property Line | Commercial Insurance                                                                                       |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                          |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                 | 415                                  | 416                   | 414                   | 454                   |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                  | $ 4                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                        | 17                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                          | $ 411                                | 407                   | 388                   | $ 279                 |                  |
| 2016 | Commercial Property Line | Commercial Insurance                                                                                       |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                          |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                 | 541                                  | 551                   | 590                   |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                  | $ 4                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                        | 17                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                          | $ 528                                | 504                   | $ 358                 |                  |                  |
| 2017 | Commercial Property Line | Commercial Insurance                                                                                       |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                          |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                 | 560                                  | 587                   |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                  | $ 12                                 |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                        | 18                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                          | $ 522                                | $ 395                 |                  |                  |                  |
| 2018 | Commercial Property Line | Commercial Insurance                                                                                       |                                 |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                          |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                 | 630                                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                  | $ 13                                 |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                        | 16                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                          | $ 386                                |                  |                  |                  |                  |

| 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.
+ References
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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