| **Property Casualty Loss And Loss Expenses (Claims Development - Workers Compensation) (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 ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($) | Dec. 31, 2011 USD ($) | Dec. 31, 2010 USD ($) | Dec. 31, 2009 USD ($) |
|-----------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | $ 2,588                              |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Liabilities for loss and ALAE, net of reinsurance                                                                                             | 5,366                                |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Workers' Compensation Line | Commercial Insurance                                                                                             |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 2,142                                |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | 1,493                                |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| All outstanding liabilities before, net of reinsurance                                                                                        | 283                                  |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Liabilities for loss and ALAE, net of reinsurance                                                                                             | 932                                  |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2009 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 231                                  | $ 232                 | $ 234                 | $ 234                 | $ 235                 | $ 238                 | $ 238                 | $ 263                 | $ 278                 | $ 307                 |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 17                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 27                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 204                                | 202                   | 201                   | 198                   | 193                   | 188                   | 179                   | 163                   | 132                   | $ 65                  |
| 2010 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 236                                  | 237                   | 240                   | 239                   | 240                   | 242                   | 248                   | 274                   | 283                   |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 20                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 26                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 207                                | 204                   | 202                   | 198                   | 192                   | 181                   | 164                   | 134                   | $ 67                  |                  |
| 2011 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 229                                  | 231                   | 236                   | 239                   | 242                   | 246                   | 251                   | 284                   |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 20                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 24                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 195                                | 192                   | 190                   | 186                   | 177                   | 161                   | 131                   | $ 65                  |                  |                  |
| 2012 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 209                                  | 211                   | 213                   | 220                   | 234                   | 245                   | 265                   |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 22                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 21                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 178                                | 175                   | 171                   | 162                   | 147                   | 121                   | $ 62                  |                  |                  |                  |
| 2013 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 205                                  | 208                   | 212                   | 221                   | 246                   | 264                   |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 23                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 20                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 168                                | 164                   | 157                   | 144                   | 119                   | $ 61                  |                  |                  |                  |                  |
| 2014 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 201                                  | 203                   | 214                   | 233                   | 261                   |                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 20                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 19                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 157                                | 148                   | 134                   | 110                   | $ 56                  |                  |                  |                  |                  |                  |
| 2015 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 195                                  | 208                   | 220                   | 246                   |                  |                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 46                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 17                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 129                                | 115                   | 93                    | $ 47                  |                  |                  |                  |                  |                  |                  |
| 2016 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 206                                  | 218                   | 230                   |                  |                  |                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 51                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 16                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 119                                | 97                    | $ 46                  |                  |                  |                  |                  |                  |                  |                  |
| 2017 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 208                                  | 218                   |                  |                  |                  |                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 74                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 15                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 88                                 | $ 45                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2018 | Workers' Compensation Line | Commercial Insurance                                                                                      |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Claims Development [Line Items]**                                                                                                           |                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance                                                                                                  | 222                                  |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses                                                   | $ 99                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                                                                         | 13                                   |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                                                                           | $ 48                                 |                  |                  |                  |                  |                  |                  |                  |                  |                  |

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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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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.
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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.
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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.
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Number of reported claims for short-duration insurance contracts.
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