| **Claims Development - Personal Auto (Details) reported_claim in Thousands, $ in Millions** | Dec. 31, 2022 USD ($) reported_claim | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) |
|---------------------------------------------------------------------------------------------|--------------------------------------|-----------------------|-----------------------|-----------------------|-----------------------|
| **Claims Development**                                                                      |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance for the years ended December 31,               | $ 3,312                              |                  |                  |                  |                  |
| Liabilities for loss and ALAE, net of reinsurance                                           | 7,967                                |                  |                  |                  |                  |
| Personal Auto | Personal Insurance                                                          |                                 |                  |                  |                  |                  |
| **Claims Development**                                                                      |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance for the years ended December 31,               | 1,831                                |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                         | 1,557                                |                  |                  |                  |                  |
| All outstanding liabilities before, net of reinsurance                                      | 13                                   |                  |                  |                  |                  |
| Liabilities for loss and ALAE, net of reinsurance                                           | 287                                  |                  |                  |                  |                  |
| 2018 | Personal Auto | Personal Insurance                                                   |                                 |                  |                  |                  |                  |
| **Claims Development**                                                                      |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance for the years ended December 31,               | 401                                  | $ 398                 | $ 395                 | $ 398                 | $ 424                 |
| Total of incurred but not reported liabilities plus expected development on reported losses | $ 3                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                       | 111                                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                         | $ 391                                | 379                   | 358                   | 327                   | $ 262                 |
| 2019 | Personal Auto | Personal Insurance                                                   |                                 |                  |                  |                  |                  |
| **Claims Development**                                                                      |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance for the years ended December 31,               | 383                                  | 380                   | 383                   | 399                   |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses | $ 4                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                       | 102                                  |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                         | $ 363                                | 346                   | 314                   | $ 250                 |                  |
| 2020 | Personal Auto | Personal Insurance                                                   |                                 |                  |                  |                  |                  |
| **Claims Development**                                                                      |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance for the years ended December 31,               | 277                                  | 281                   | 305                   |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses | $ 7                                  |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                       | 71                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                         | $ 248                                | 225                   | $ 186                 |                  |                  |
| 2021 | Personal Auto | Personal Insurance                                                   |                                 |                  |                  |                  |                  |
| **Claims Development**                                                                      |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance for the years ended December 31,               | 343                                  | 350                   |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses | $ 14                                 |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                       | 80                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                         | $ 278                                | $ 219                 |                  |                  |                  |
| 2022 | Personal Auto | Personal Insurance                                                   |                                 |                  |                  |                  |                  |
| **Claims Development**                                                                      |                                 |                  |                  |                  |                  |
| Incurred losses and ALAE, net of reinsurance for the years ended December 31,               | 427                                  |                  |                  |                  |                  |
| Total of incurred but not reported liabilities plus expected development on reported losses | $ 58                                 |                  |                  |                  |                  |
| Cumulative number of reported claims | reported_claim                                       | 80                                   |                  |                  |                  |                  |
| Cumulative paid losses and ALAE, net of reinsurance                                         | $ 277                                |                  |                  |                  |                  |

| X                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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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.
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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.
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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.
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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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| - 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.
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Cumulative number of reported claims for short-duration insurance contracts.
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