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Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Commercial - General Liability - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - General Liability - 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 | $ 6,670 |  |  |  |  |  |  |  |  |
IBNR | 2,006 |  |  |  |  |  |  |  |  |
2012 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | 632 | $ 632 | $ 630 | $ 635 | $ 635 | $ 619 | $ 636 | $ 639 | $ 611 | $ 587
IBNR | $ 20 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 35,313 |  |  |  |  |  |  |  |  |
2013 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 624 | 623 | 620 | 623 | 613 | 655 | 650 | 655 | $ 650 |
IBNR | $ 24 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 33,706 |  |  |  |  |  |  |  |  |
2014 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 659 | 659 | 658 | 635 | 631 | 654 | 658 | $ 653 |  |
IBNR | $ 28 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 28,064 |  |  |  |  |  |  |  |  |
2015 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 617 | 602 | 600 | 589 | 574 | 576 | $ 581 |  |  |
IBNR | $ 42 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 24,118 |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 683 | 673 | 671 | 667 | 659 | $ 623 |  |  |  |
IBNR | $ 68 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 24,511 |  |  |  |  |  |  |  |  |
2017 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 630 | 634 | 632 | 632 | $ 632 |  |  |  |  |
IBNR | $ 67 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 22,195 |  |  |  |  |  |  |  |  |
2018 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 639 | 646 | 644 | $ 653 |  |  |  |  |  |
IBNR | $ 205 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 19,917 |  |  |  |  |  |  |  |  |
2019 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 682 | 682 | $ 680 |  |  |  |  |  |  |
IBNR | $ 330 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 18,602 |  |  |  |  |  |  |  |  |
2020 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 722 | $ 723 |  |  |  |  |  |  |  |
IBNR | $ 516 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 13,028 |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 782 |  |  |  |  |  |  |  |  |
IBNR | $ 706 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 9,759 |  |  |  |  |  |  |  |  |

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