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Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Commercial - Workers' Compensation - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Workers' Compensation - Commercial $ in Millions | Dec. 31, 2021 USD ($) claim | Dec. 31, 2020 USD ($) | 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 ($) | Dec. 31, 2012 USD ($)
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Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 4,575 |  |  |  |  |  |  |  |  |
IBNR | 1,325 |  |  |  |  |  |  |  |  |
2012 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | 664 | $ 663 | $ 668 | $ 671 | $ 673 | $ 678 | $ 669 | $ 659 | $ 627 | $ 601
IBNR | $ 66 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 42,804 |  |  |  |  |  |  |  |  |
2013 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 548 | 552 | 561 | 582 | 593 | 618 | 592 | 572 | $ 537 |
IBNR | $ 91 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 38,867 |  |  |  |  |  |  |  |  |
2014 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 448 | 439 | 446 | 450 | 452 | 479 | 480 | $ 467 |  |
IBNR | $ 105 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 33,502 |  |  |  |  |  |  |  |  |
2015 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 372 | 382 | 394 | 408 | 406 | 431 | $ 422 |  |  |
IBNR | $ 101 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 31,894 |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 355 | 366 | 382 | 396 | 405 | $ 426 |  |  |  |
IBNR | $ 104 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 31,981 |  |  |  |  |  |  |  |  |
2017 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 402 | 400 | 421 | 432 | $ 440 |  |  |  |  |
IBNR | $ 92 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 33,121 |  |  |  |  |  |  |  |  |
2018 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 415 | 428 | 440 | $ 450 |  |  |  |  |  |
IBNR | $ 104 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 34,851 |  |  |  |  |  |  |  |  |
2019 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 437 | 449 | $ 452 |  |  |  |  |  |  |
IBNR | $ 134 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 34,248 |  |  |  |  |  |  |  |  |
2020 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 466 | $ 477 |  |  |  |  |  |  |  |
IBNR | $ 228 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 29,188 |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 468 |  |  |  |  |  |  |  |  |
IBNR | $ 300 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 25,711 |  |  |  |  |  |  |  |  |

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