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Insurance - Short-duration insurance contracts, claims development (Details) - Property and casualty insurance $ in Millions | Dec. 31, 2020 USD ($) claim | Dec. 31, 2019 USD ($) | 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 ($) | Dec. 31, 2011 USD ($)
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 21,886 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | 16,231 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE — 11th year and prior (excluding unallocated LAE) | 467 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | 6,122 |  |  |  |  |  |  |  |  |
Accident Year 2011 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 1,829 | $ 1,832 | $ 1,843 | $ 1,859 | $ 1,866 | $ 1,861 | $ 1,871 | $ 1,849 | $ 1,848 | $ 1,840
Total IBNR Plus Expected Development on Reported Claims | $ 35 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 209,666 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,762 | 1,750 | 1,734 | 1,711 | 1,682 | 1,629 | 1,534 | 1,389 | 1,181 | 609
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 96.30% |  |  |  |  |  |  |  |  |
Accident Year 2012 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,875 | 1,886 | 1,906 | 1,941 | 1,955 | 1,947 | 1,946 | 1,952 | 1,970 |
Total IBNR Plus Expected Development on Reported Claims | $ 43 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 218,995 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,805 | 1,788 | 1,785 | 1,735 | 1,675 | 1,579 | 1,418 | 1,214 | 824 |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 96.30% |  |  |  |  |  |  |  |  |
Accident Year 2013 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,956 | 1,969 | 1,982 | 2,000 | 1,996 | 2,000 | 2,011 | 2,036 |  |
Total IBNR Plus Expected Development on Reported Claims | $ 65 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 222,463 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,851 | 1,824 | 1,774 | 1,714 | 1,617 | 1,443 | 1,214 | 697 |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 94.60% |  |  |  |  |  |  |  |  |
Accident Year 2014 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,957 | 1,978 | 2,004 | 2,038 | 2,040 | 2,050 | 2,083 |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 88 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 219,309 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,812 | 1,773 | 1,705 | 1,588 | 1,422 | 1,174 | 594 |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 92.60% |  |  |  |  |  |  |  |  |
Accident Year 2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 2,013 | 2,022 | 2,038 | 2,041 | 2,047 | 2,114 |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 125 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 230,235 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,791 | 1,722 | 1,592 | 1,404 | 1,129 | 619 |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 89.00% |  |  |  |  |  |  |  |  |
Accident Year 2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 2,034 | 2,060 | 2,082 | 2,083 | 2,117 |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 213 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 222,410 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,662 | 1,539 | 1,350 | 1,099 | 577 |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 81.70% |  |  |  |  |  |  |  |  |
Accident Year 2017 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 2,301 | 2,329 | 2,348 | 2,375 |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 342 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 245,799 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,736 | 1,524 | 1,250 | 709 |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 75.40% |  |  |  |  |  |  |  |  |
Accident Year 2018 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 2,499 | 2,516 | 2,507 |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 552 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 234,457 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,606 | 1,337 | 730 |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 64.30% |  |  |  |  |  |  |  |  |
Accident Year 2019 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 2,674 | 2,721 |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 797 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 250,429 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 1,448 | 847 |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 54.20% |  |  |  |  |  |  |  |  |
Accident year 2020 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 2,748 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 1,410 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 182,219 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 758 |  |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 27.60% |  |  |  |  |  |  |  |  |
Excludes short-duration insurance contracts detail for accident years not separately presented |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | $ 5,655 |  |  |  |  |  |  |  |  |
Property and transportation |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 8,673 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | 7,497 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE — 11th year and prior (excluding unallocated LAE) | 20 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | 1,196 |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2011 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 843 | 843 | 844 | 846 | 850 | 837 | 827 | 813 | 799 | 811
Total IBNR Plus Expected Development on Reported Claims | $ 4 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 138,334 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 835 | 834 | 833 | 829 | 821 | 803 | 771 | 727 | 667 | 365
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 99.10% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2012 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 879 | 881 | 886 | 890 | 894 | 883 | 871 | 857 | 864 |
Total IBNR Plus Expected Development on Reported Claims | $ 4 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 143,151 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 872 | 869 | 882 | 856 | 842 | 816 | 772 | 708 | 572 |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 99.20% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2013 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 871 | 873 | 877 | 878 | 878 | 872 | 870 | 882 |  |
Total IBNR Plus Expected Development on Reported Claims | $ 7 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 138,925 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 860 | 858 | 847 | 831 | 804 | 760 | 702 | 438 |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 98.70% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2014 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 804 | 808 | 815 | 820 | 817 | 828 | 844 |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 8 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 133,182 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 789 | 783 | 770 | 744 | 693 | 632 | 329 |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 98.10% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 772 | 777 | 777 | 779 | 784 | 818 |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 15 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 134,875 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 744 | 736 | 707 | 667 | 582 | 359 |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 96.40% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 694 | 706 | 714 | 716 | 746 |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 25 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 121,116 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 640 | 618 | 577 | 521 | 294 |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 92.20% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2017 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 823 | 843 | 847 | 889 |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 39 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 140,549 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 735 | 696 | 640 | 379 |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 89.30% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2018 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 886 | 902 | 932 |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 69 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 129,891 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 738 | 676 | 396 |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 83.30% |  |  |  |  |  |  |  |  |
Property and transportation | Accident Year 2019 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,058 | 1,111 |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 125 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 152,304 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 823 | 527 |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 77.80% |  |  |  |  |  |  |  |  |
Property and transportation | Accident year 2020 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,043 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 349 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 109,446 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 461 |  |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 44.20% |  |  |  |  |  |  |  |  |
Property and transportation | Excludes short-duration insurance contracts detail for accident years not separately presented |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | $ 1,176 |  |  |  |  |  |  |  |  |
Specialty casualty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 10,763 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | 6,876 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE — 11th year and prior (excluding unallocated LAE) | 415 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | 4,302 |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2011 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 808 | 810 | 817 | 826 | 828 | 834 | 848 | 839 | 849 | 852
Total IBNR Plus Expected Development on Reported Claims | $ 29 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 54,961 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 755 | 745 | 731 | 714 | 694 | 662 | 612 | 522 | 383 | 174
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 93.40% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2012 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 833 | 842 | 849 | 877 | 883 | 885 | 885 | 892 | 901 |
Total IBNR Plus Expected Development on Reported Claims | $ 35 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 54,752 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 775 | 761 | 745 | 723 | 684 | 621 | 516 | 385 | 173 |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 93.00% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2013 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 905 | 916 | 926 | 945 | 940 | 945 | 949 | 968 |  |
Total IBNR Plus Expected Development on Reported Claims | $ 53 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 55,063 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 820 | 797 | 766 | 729 | 666 | 554 | 396 | 182 |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 90.60% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2014 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 952 | 967 | 982 | 1,006 | 1,008 | 1,008 | 1,035 |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 71 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 56,669 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 829 | 801 | 755 | 680 | 574 | 412 | 190 |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 87.10% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,021 | 1,024 | 1,042 | 1,041 | 1,043 | 1,081 |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 99 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 57,745 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 844 | 792 | 702 | 577 | 411 | 178 |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 82.70% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,090 | 1,101 | 1,116 | 1,122 | 1,131 |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 164 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 56,169 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 806 | 713 | 584 | 418 | 186 |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 73.90% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2017 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,189 | 1,204 | 1,221 | 1,211 |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 275 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 56,558 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 755 | 612 | 422 | 200 |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 63.50% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2018 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,302 | 1,307 | 1,277 |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 416 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 58,079 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 649 | 475 | 210 |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 49.80% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident Year 2019 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,311 | 1,308 |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 571 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 56,950 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 455 | 212 |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 34.70% |  |  |  |  |  |  |  |  |
Specialty casualty | Accident year 2020 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 1,352 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 844 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 48,294 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 188 |  |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 13.90% |  |  |  |  |  |  |  |  |
Specialty casualty | Excludes short-duration insurance contracts detail for accident years not separately presented |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | $ 3,887 |  |  |  |  |  |  |  |  |
Specialty financial |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 1,690 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | 1,441 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE — 11th year and prior (excluding unallocated LAE) | (2) |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | 247 |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2011 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 137 | 137 | 139 | 143 | 144 | 147 | 153 | 155 | 157 | 138
Total IBNR Plus Expected Development on Reported Claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 16,371 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 133 | 132 | 132 | 131 | 131 | 130 | 123 | 115 | 111 | 58
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 97.10% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2012 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 126 | 127 | 132 | 135 | 137 | 139 | 151 | 163 | 163 |
Total IBNR Plus Expected Development on Reported Claims | $ 2 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 21,092 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 125 | 126 | 128 | 126 | 121 | 117 | 109 | 104 | 71 |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 99.20% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2013 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 122 | 122 | 126 | 127 | 131 | 137 | 145 | 140 |  |
Total IBNR Plus Expected Development on Reported Claims | $ 4 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 28,475 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 118 | 118 | 117 | 117 | 113 | 107 | 100 | 70 |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 96.70% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2014 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 137 | 142 | 147 | 153 | 156 | 157 | 146 |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 2 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 29,458 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 141 | 139 | 137 | 128 | 125 | 109 | 62 |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 102.90% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 138 | 145 | 153 | 158 | 160 | 156 |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 4 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 37,615 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 134 | 132 | 133 | 129 | 110 | 72 |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 97.10% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 174 | 182 | 187 | 184 | 179 |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 8 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 45,125 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 163 | 161 | 158 | 141 | 88 |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 93.70% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2017 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 208 | 212 | 215 | 212 |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 15 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 48,692 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 194 | 186 | 169 | 120 |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 93.30% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2018 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 219 | 217 | 212 |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 27 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 46,487 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 187 | 163 | 112 |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 85.40% |  |  |  |  |  |  |  |  |
Specialty financial | Accident Year 2019 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 198 | 194 |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 37 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 41,175 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 146 | 99 |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 73.70% |  |  |  |  |  |  |  |  |
Specialty financial | Accident year 2020 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 231 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 115 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 24,479 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 100 |  |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 43.30% |  |  |  |  |  |  |  |  |
Specialty financial | Excludes short-duration insurance contracts detail for accident years not separately presented |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | $ 249 |  |  |  |  |  |  |  |  |
Other specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 760 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | 417 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE — 11th year and prior (excluding unallocated LAE) | 34 |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | 377 |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2011 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | 41 | 42 | 43 | 44 | 44 | 43 | 43 | 42 | 43 | 39
Total IBNR Plus Expected Development on Reported Claims | $ 2 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 39 | 39 | 38 | 37 | 36 | 34 | 28 | 25 | 20 | $ 12
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 95.10% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2012 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 37 | 36 | 39 | 39 | 41 | 40 | 39 | 40 | 42 |
Total IBNR Plus Expected Development on Reported Claims | $ 2 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 33 | 32 | 30 | 30 | 28 | 25 | 21 | 17 | $ 8 |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 89.20% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2013 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 58 | 58 | 53 | 50 | 47 | 46 | 47 | 46 |  |
Total IBNR Plus Expected Development on Reported Claims | $ 1 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 53 | 51 | 44 | 37 | 34 | 22 | 16 | $ 7 |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 91.40% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2014 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 64 | 61 | 60 | 59 | 59 | 57 | 58 |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 7 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 53 | 50 | 43 | 36 | 30 | 21 | $ 13 |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 82.80% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 82 | 76 | 66 | 63 | 60 | 59 |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 7 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 69 | 62 | 50 | 31 | 26 | $ 10 |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 84.10% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 76 | 71 | 65 | 61 | 61 |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 16 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 53 | 47 | 31 | 19 | $ 9 |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 69.70% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2017 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 81 | 70 | 65 | 63 |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 13 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 52 | 30 | 19 | $ 10 |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 64.20% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2018 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 92 | 90 | 86 |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 40 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 32 | 23 | $ 12 |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 34.80% |  |  |  |  |  |  |  |  |
Other specialty | Accident Year 2019 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 107 | 108 |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 64 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 24 | $ 9 |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 22.40% |  |  |  |  |  |  |  |  |
Other specialty | Accident year 2020 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated LAE, Net of Reinsurance | $ 122 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 102 |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | claim | 0 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Allocated LAE, Net of Reinsurance | $ 9 |  |  |  |  |  |  |  |  |
Cumulative Percentage Paid of Incurred Claims and Allocated LAE, Net of Reinsurance | 7.40% |  |  |  |  |  |  |  |  |
Other specialty | Excludes short-duration insurance contracts detail for accident years not separately presented |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid losses and LAE, net of reinsurance (excluding unallocated LAE) | $ 343 |  |  |  |  |  |  |  |  |

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