| **Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Commercial - Workers' Compensation - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Workers' Compensation - Commercial $ in Millions** | Dec. 31, 2022 USD ($) claim | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|-----------------------|
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 4,298                     |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | 1,286                       |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2013                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | 537                         | $ 548                 | $ 552                 | $ 561                 | $ 582                 | $ 593                 | $ 618                 | $ 592                 | $ 572                 | $ 537                 |
| IBNR                                                                                                                                                                                                                                               | $ 82                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 38,979                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2014                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 430                       | 448                   | 439                   | 446                   | 450                   | 452                   | 479                   | 480                   | $ 467                 |                  |
| IBNR                                                                                                                                                                                                                                               | $ 76                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 33,522                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2015                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 353                       | 372                   | 382                   | 394                   | 408                   | 406                   | 431                   | $ 422                 |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 80                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 31,899                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2016                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 331                       | 355                   | 366                   | 382                   | 396                   | 405                   | $ 426                 |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 77                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 31,991                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2017                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 399                       | 402                   | 400                   | 421                   | 432                   | $ 440                 |                  |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 81                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 33,130                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2018                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 415                       | 415                   | 428                   | 440                   | $ 450                 |                  |                  |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 93                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 34,875                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2019                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 436                       | 437                   | 449                   | $ 452                 |                  |                  |                  |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 105                       |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 34,324                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2020                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 446                       | 466                   | $ 477                 |                  |                  |                  |                  |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 182                       |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 29,392                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2021                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 454                       | $ 468                 |                  |                  |                  |                  |                  |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 202                       |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 29,886                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| 2022                                                                                                                                                                                                                                               |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| **Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]**                                                                                                                                              |                        |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Incurred claims and allocated claim adjustment expense, net                                                                                                                                                                                        | $ 497                       |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| IBNR                                                                                                                                                                                                                                               | $ 308                       |                  |                  |                  |                  |                  |                  |                  |                  |                  |
| Cumulative Number of Claims | claim                                                                                                                                                                                                                | 28,753                      |                  |                  |                  |                  |                  |                  |                  |                  |                  |

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| - Definition
[Line Items] for Net Incurred Claim and Claim Adjustment Expense [Table]
+ References
No definition available.
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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
Cumulative number of reported claims for short-duration insurance contracts.
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