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Claim and Claim Adjustment Expense Reserves (Commercial - General Liability - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - General Liability - Commercial $ in Millions | Dec. 31, 2024 USD ($) claim | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
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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 | $ 8,296 |  |  |  |  |  |  |  |  |
IBNR | 3,215 |  |  |  |  |  |  |  |  |
2015 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | 656 | $ 639 | $ 625 | $ 617 | $ 602 | $ 600 | $ 589 | $ 574 | $ 576 | $ 581
IBNR | $ 39 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 24,309 |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 712 | 704 | 684 | 683 | 673 | 671 | 667 | 659 | $ 623 |
IBNR | $ 27 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 24,901 |  |  |  |  |  |  |  |  |
2017 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 713 | 690 | 652 | 630 | 634 | 632 | 632 | $ 632 |  |
IBNR | $ 16 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 22,544 |  |  |  |  |  |  |  |  |
2018 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 665 | 679 | 650 | 639 | 646 | 644 | $ 653 |  |  |
IBNR | $ 83 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 20,553 |  |  |  |  |  |  |  |  |
2019 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 727 | 720 | 691 | 682 | 682 | $ 680 |  |  |  |
IBNR | $ 129 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 19,907 |  |  |  |  |  |  |  |  |
2020 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 702 | 736 | 726 | 722 | $ 723 |  |  |  |  |
IBNR | $ 237 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 14,964 |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 814 | 793 | 784 | $ 782 |  |  |  |  |  |
IBNR | $ 299 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 15,952 |  |  |  |  |  |  |  |  |
2022 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 930 | 928 | $ 929 |  |  |  |  |  |  |
IBNR | $ 515 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 17,527 |  |  |  |  |  |  |  |  |
2023 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 1,106 | $ 1,071 |  |  |  |  |  |  |  |
IBNR | $ 726 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 17,037 |  |  |  |  |  |  |  |  |
2024 |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net | $ 1,271 |  |  |  |  |  |  |  |  |
IBNR | $ 1,144 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | claim | 14,632 |  |  |  |  |  |  |  |  |

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