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Unpaid losses and loss adjustment expenses - Losses and allocated loss adjustment expenses Incurred (Detail) - Insurance Group [Member] Claim in Thousands, $ in Millions | Dec. 31, 2024 USD ($) Claim | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | [1] | Dec. 31, 2021 USD ($) | [1] | Dec. 31, 2020 USD ($) | [1] | Dec. 31, 2019 USD ($) | [1] | Dec. 31, 2018 USD ($) | [1] | Dec. 31, 2017 USD ($) | [1] | Dec. 31, 2016 USD ($) | [1] | Dec. 31, 2015 USD ($) | [1]
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 104,671 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 22,995 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 22,266 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 885 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 11,900 | $ 12,273 |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 11,771 | 11,567 |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 111 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 7,430 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 11,095 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 10,495 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ (454) |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 6,380 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | 2023-2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 729 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | Before 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | 156 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 84,467 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 64,539 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 20,818 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 13,462 | 13,593 | [1] | $ 13,697 | $ 14,024 | $ 14,637 |  |  |  |  |
Cumulative Losses and ALAE Paid | 12,946 | 12,608 | [1] | 11,794 | 9,839 | 5,395 |  |  |  |  |
IBNR and Case Development Liabilities | $ 382 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 2,127 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 17,033 | 17,229 | [1] | 17,457 | 17,481 |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 15,796 | 14,863 | [1] | 12,681 | 6,450 |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 907 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 2,457 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 18,818 | 18,903 | [1] | 19,645 |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 16,031 | 13,838 | [1] | 7,614 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 2,065 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 2,387 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 18,073 | 17,948 | [1] |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 12,682 | 7,191 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 3,864 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 1,956 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 17,081 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 7,084 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 4,730 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 1,694 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2020-2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 19,928 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | Before 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | 890 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 15,742 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 6,802 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 9,432 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 1,010 | 1,016 | [1] | 1,033 | 1,093 | 1,157 | $ 1,218 | $ 1,290 | $ 1,269 | $ 1,342 | $ 1,374
Cumulative Losses and ALAE Paid | 879 | 843 | [1] | 799 | 719 | 663 | 543 | 382 | 218 | 108 | 23
IBNR and Case Development Liabilities | $ 37 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 12 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,172 | 1,188 | [1] | 1,216 | 1,288 | 1,341 | 1,394 | 1,414 | 1,416 | 1,392 |
Cumulative Losses and ALAE Paid | 957 | 908 | [1] | 822 | 712 | 620 | 461 | 274 | 115 | 22 |
IBNR and Case Development Liabilities | $ 78 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 15 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,310 | 1,315 | [1] | 1,349 | 1,382 | 1,474 | 1,495 | 1,499 | 1,466 |  |
Cumulative Losses and ALAE Paid | 977 | 877 | [1] | 739 | 582 | 457 | 300 | 128 | 27 |  |
IBNR and Case Development Liabilities | $ 89 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 21 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,583 | 1,606 | [1] | 1,616 | 1,580 | 1,659 | 1,650 | 1,602 |  |  |
Cumulative Losses and ALAE Paid | 1,080 | 949 | [1] | 728 | 543 | 367 | 166 | 35 |  |  |
IBNR and Case Development Liabilities | $ 140 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 24 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,579 | 1,534 | [1] | 1,614 | 1,663 | 1,691 | 1,670 |  |  |  |
Cumulative Losses and ALAE Paid | 963 | 757 | [1] | 536 | 314 | 160 | 39 |  |  |  |
IBNR and Case Development Liabilities | $ 180 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 22 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,606 | 1,631 | [1] | 1,698 | 1,751 | 1,704 |  |  |  |  |
Cumulative Losses and ALAE Paid | 767 | 531 | [1] | 321 | 148 | 34 |  |  |  |  |
IBNR and Case Development Liabilities | $ 369 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 33 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,714 | 1,787 | [1] | 1,855 | 1,852 |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 548 | 333 | [1] | 136 | 36 |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 718 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 27 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,846 | 1,912 | [1] | 1,927 |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 441 | 182 | [1] | 38 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 981 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 25 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 1,918 | 1,964 | [1] |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 156 | 28 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,428 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 27 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 2,004 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 34 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,793 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 22 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Before 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | $ 492 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Short Duration Insurance Contracts Accident Years 2015 Through 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 8,940 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 50,722 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 27,115 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 24,335 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 2,367 | 2,358 | [1] | 2,393 | 2,408 | 2,402 | 2,428 | 2,426 | 2,455 | 2,539 | 2,580
Cumulative Losses and ALAE Paid | 2,095 | 2,070 | [1] | 2,041 | 1,966 | 1,873 | 1,766 | 1,507 | 1,187 | 804 | 329
IBNR and Case Development Liabilities | $ 178 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 120 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 2,809 | 2,840 | [1] | 2,864 | 2,825 | 2,815 | 2,772 | 2,793 | 2,848 | 2,931 |
Cumulative Losses and ALAE Paid | 2,420 | 2,377 | [1] | 2,303 | 2,140 | 1,998 | 1,765 | 1,359 | 908 | 373 |
IBNR and Case Development Liabilities | $ 277 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 125 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 3,357 | 3,321 | [1] | 3,320 | 3,322 | 3,310 | 3,299 | 3,337 | 3,473 |  |
Cumulative Losses and ALAE Paid | 2,784 | 2,673 | [1] | 2,492 | 2,279 | 2,050 | 1,645 | 1,133 | 480 |  |
IBNR and Case Development Liabilities | $ 395 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 143 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 4,230 | 4,177 | [1] | 4,091 | 4,030 | 3,967 | 3,886 | 3,998 |  |  |
Cumulative Losses and ALAE Paid | 3,396 | 3,120 | [1] | 2,746 | 2,324 | 1,902 | 1,340 | 583 |  |  |
IBNR and Case Development Liabilities | $ 570 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 164 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 4,919 | 4,847 | [1] | 4,763 | 4,692 | 4,623 | 4,584 |  |  |  |
Cumulative Losses and ALAE Paid | 3,812 | 3,430 | [1] | 2,898 | 2,214 | 1,598 | 725 |  |  |  |
IBNR and Case Development Liabilities | $ 691 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 185 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 4,866 | 4,774 | [1] | 4,775 | 4,881 | 5,030 |  |  |  |  |
Cumulative Losses and ALAE Paid | 3,138 | 2,598 | [1] | 2,066 | 1,498 | 736 |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,167 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 157 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 5,983 | 5,882 | [1] | 5,856 | 5,899 |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 3,168 | 2,440 | [1] | 1,751 | 869 |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,923 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 318 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 6,866 | 6,757 | [1] | 6,796 |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 2,905 | 2,012 | [1] | 962 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 2,801 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 316 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 7,363 | 7,299 | [1] |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 2,152 | 1,056 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 3,887 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 187 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | $ 7,962 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 1,245 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 5,552 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 169 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Before 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | $ 728 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Short Duration Insurance Contracts Accident Years 2015 Through 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 23,607 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 59,362 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 43,998 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 15,851 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 3,225 | 3,255 | [1] | 3,232 | 3,238 | 3,236 | 3,214 | 3,218 | 2,827 | 3,392 | 3,587
Cumulative Losses and ALAE Paid | 2,966 | 2,917 | [1] | 2,843 | 2,791 | 2,705 | 2,522 | 2,414 | 2,196 | 1,793 | 669
IBNR and Case Development Liabilities | 94 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 4,091 | 4,088 | [1] | 4,099 | 4,121 | 4,132 | 4,134 | 4,170 | 4,492 | 3,905 |
Cumulative Losses and ALAE Paid | 3,889 | 3,802 | [1] | 3,724 | 3,615 | 3,419 | 3,151 | 2,662 | 2,203 | 913 |
IBNR and Case Development Liabilities | 30 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 5,577 | 5,590 | [1] | 5,608 | 5,689 | 5,767 | 5,893 | 6,071 | 6,374 |  |
Cumulative Losses and ALAE Paid | 5,456 | 5,432 | [1] | 5,343 | 5,150 | 4,915 | 4,564 | 3,494 | 1,346 |  |
IBNR and Case Development Liabilities | 51 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 5,238 | 5,218 | [1] | 5,267 | 5,260 | 5,402 | 5,542 | 5,456 |  |  |
Cumulative Losses and ALAE Paid | 4,571 | 4,444 | [1] | 4,236 | 3,992 | 3,709 | 3,073 | 1,204 |  |  |
IBNR and Case Development Liabilities | 207 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 4,447 | 4,488 | [1] | 4,537 | 4,838 | 5,064 | 4,951 |  |  |  |
Cumulative Losses and ALAE Paid | 4,082 | 4,018 | [1] | 3,856 | 3,532 | 2,826 | 1,009 |  |  |  |
IBNR and Case Development Liabilities | 112 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 6,450 | 6,620 | [1] | 6,825 | 7,188 | 6,914 |  |  |  |  |
Cumulative Losses and ALAE Paid | 5,546 | 5,275 | [1] | 4,613 | 3,569 | 1,252 |  |  |  |  |
IBNR and Case Development Liabilities | 376 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 7,289 | 7,585 | [1] | 7,919 | 8,063 |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 6,073 | 5,377 | [1] | 4,070 | 1,621 |  |  |  |  |  |
IBNR and Case Development Liabilities | 450 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 7,916 | 8,412 | [1] | 8,852 |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 5,588 | 4,322 | [1] | 1,813 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 1,102 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 7,379 | 7,953 | [1] |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 4,107 | 1,771 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 1,632 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 7,750 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 1,720 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 4,225 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Before 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 487 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Short Duration Insurance Contracts Accident Years 2015 Through 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 15,364 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 52,757 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 28,849 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 33,350 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 3,276 | 3,300 | [1] | 3,298 | 3,351 | 3,388 | 3,426 | 3,568 | 3,655 | 3,615 | 3,409
Cumulative Losses and ALAE Paid | 2,678 | 2,582 | [1] | 2,473 | 2,338 | 2,190 | 1,996 | 1,724 | 1,425 | 990 | $ 445
IBNR and Case Development Liabilities | 311 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 3,793 | 3,763 | [1] | 3,735 | 3,765 | 3,808 | 3,859 | 3,891 | 3,987 | 3,777 |
Cumulative Losses and ALAE Paid | 3,095 | 2,957 | [1] | 2,782 | 2,607 | 2,414 | 2,143 | 1,795 | 1,355 | $ 653 |
IBNR and Case Development Liabilities | 370 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 4,214 | 4,211 | [1] | 4,154 | 4,164 | 4,232 | 4,339 | 4,462 | 4,028 |  |
Cumulative Losses and ALAE Paid | 3,350 | 3,164 | [1] | 2,938 | 2,720 | 2,472 | 1,823 | 1,306 | $ 605 |  |
IBNR and Case Development Liabilities | 432 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 5,429 | 5,359 | [1] | 5,273 | 5,345 | 5,476 | 5,523 | 4,875 |  |  |
Cumulative Losses and ALAE Paid | 4,224 | 3,948 | [1] | 3,631 | 3,252 | 2,786 | 1,737 | $ 693 |  |  |
IBNR and Case Development Liabilities | 647 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 5,751 | 5,678 | [1] | 5,718 | 5,885 | 6,025 | 5,559 |  |  |  |
Cumulative Losses and ALAE Paid | 4,094 | 3,727 | [1] | 3,181 | 2,414 | 1,865 | $ 839 |  |  |  |
IBNR and Case Development Liabilities | 1,002 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 6,053 | 6,079 | [1] | 6,033 | 6,215 | 6,203 |  |  |  |  |
Cumulative Losses and ALAE Paid | 3,967 | 3,373 | [1] | 2,709 | 1,900 | $ 866 |  |  |  |  |
IBNR and Case Development Liabilities | 1,371 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 5,959 | 5,942 | [1] | 6,270 | 6,300 |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 3,225 | 2,654 | [1] | 1,781 | $ 765 |  |  |  |  |  |
IBNR and Case Development Liabilities | 1,838 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 6,045 | 6,092 | [1] | 6,047 |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 1,963 | 1,333 | [1] | $ 620 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 2,829 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 6,144 | 6,053 | [1] |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 1,575 | $ 689 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 3,528 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Losses and ALAE incurred | 6,093 |  |  |  |  |  |  |  |  |  |
Cumulative Losses and ALAE Paid | 678 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 4,660 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Before 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | 9,442 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Short Duration Insurance Contracts Accident Years 2015 Through 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 23,908 |  |  |  |  |  |  |  |  |  |
[1] | Unaudited required supplemental information

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