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Unpaid losses and loss adjustment expenses - Incurred and paid losses and allocated loss adjustment expenses (Detail) - Insurance Group [Member] Claim in Thousands, $ in Millions | Dec. 31, 2023 USD ($) Claim | Dec. 31, 2022 USD ($) | 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 ($) | [1] | Dec. 31, 2014 USD ($) | [1]
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 100,502 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 25,972 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 25,298 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 737 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 13,699 | $ 14,138 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 13,731 | 13,251 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ (56) |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 9,161 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 12,273 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 11,567 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ (691) |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 7,295 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | 2022-2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 674 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Physical Damage [Member] | Before 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | 63 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 83,841 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 64,093 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 20,477 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 16,168 | 16,151 | [1] | $ 16,191 | $ 16,678 | $ 16,901 |  |  |  |  |
Cumulative Paid Losses and ALAE | 15,593 | 15,084 | [1] | 13,851 | 11,671 | 6,742 |  |  |  |  |
IBNR and Case Development Liabilities | $ 348 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 2,797 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 13,593 | 13,697 | [1] | 14,024 | 14,637 |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 12,608 | 11,794 | [1] | 9,839 | 5,395 |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 666 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 2,123 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 17,229 | 17,457 | [1] | 17,481 |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 14,863 | 12,681 | [1] | 6,450 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,559 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 2,446 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 18,903 | 19,645 | [1] |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 13,838 | 7,614 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 3,316 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 2,360 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 17,948 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 7,191 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 5,567 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 1,804 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | 2019-2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 19,748 |  |  |  |  |  |  |  |  |  |
GEICO [Member] | Auto Liability [Member] | Before 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | 729 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 14,960 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 6,277 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 9,166 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 1,007 | 1,029 | [1] | 1,033 | 1,061 | 1,127 | $ 1,218 | $ 1,246 | $ 1,305 | $ 1,375 | $ 1,370
Cumulative Paid Losses and ALAE | 869 | 840 | [1] | 788 | 752 | 671 | 540 | 396 | 238 | 106 | 21
IBNR and Case Development Liabilities | $ 45 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 11 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,016 | 1,033 | [1] | 1,093 | 1,157 | 1,218 | 1,290 | 1,269 | 1,342 | 1,374 |
Cumulative Paid Losses and ALAE | 843 | 799 | [1] | 719 | 663 | 543 | 382 | 218 | 108 | 23 |
IBNR and Case Development Liabilities | $ 55 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 12 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,188 | 1,216 | [1] | 1,288 | 1,341 | 1,394 | 1,414 | 1,416 | 1,392 |  |
Cumulative Paid Losses and ALAE | 908 | 822 | [1] | 712 | 620 | 461 | 274 | 115 | 22 |  |
IBNR and Case Development Liabilities | $ 105 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 15 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,315 | 1,349 | [1] | 1,382 | 1,474 | 1,495 | 1,499 | 1,466 |  |  |
Cumulative Paid Losses and ALAE | 877 | 739 | [1] | 582 | 457 | 300 | 128 | 27 |  |  |
IBNR and Case Development Liabilities | $ 117 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 21 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,606 | 1,616 | [1] | 1,580 | 1,659 | 1,650 | 1,602 |  |  |  |
Cumulative Paid Losses and ALAE | 949 | 728 | [1] | 543 | 367 | 166 | 35 |  |  |  |
IBNR and Case Development Liabilities | $ 205 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 24 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,534 | 1,614 | [1] | 1,663 | 1,691 | 1,670 |  |  |  |  |
Cumulative Paid Losses and ALAE | 757 | 536 | [1] | 314 | 160 | 39 |  |  |  |  |
IBNR and Case Development Liabilities | $ 320 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 21 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,631 | 1,698 | [1] | 1,751 | 1,704 |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 531 | 321 | [1] | 148 | 34 |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 615 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 32 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,787 | 1,855 | [1] | 1,852 |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 333 | 136 | [1] | 36 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,053 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 25 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,912 | 1,927 | [1] |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 182 | 38 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,403 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 20 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 1,964 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 28 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,781 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 17 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Before 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | $ 483 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Short Duration Insurance Contracts Accident Years 2014 Through 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 8,683 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 44,065 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 23,422 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 21,230 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 1,810 | 1,829 | [1] | 1,861 | 1,875 | 1,906 | 1,901 | 1,970 | 2,036 | 2,064 | 2,138
Cumulative Paid Losses and ALAE | 1,646 | 1,617 | [1] | 1,600 | 1,557 | 1,504 | 1,407 | 1,269 | 1,002 | 683 | 286
IBNR and Case Development Liabilities | $ 115 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 103 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 2,358 | 2,393 | [1] | 2,408 | 2,402 | 2,428 | 2,426 | 2,455 | 2,539 | 2,580 |
Cumulative Paid Losses and ALAE | 2,070 | 2,041 | [1] | 1,966 | 1,873 | 1,766 | 1,507 | 1,187 | 804 | 329 |
IBNR and Case Development Liabilities | $ 201 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 120 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 2,840 | 2,864 | [1] | 2,825 | 2,815 | 2,772 | 2,793 | 2,848 | 2,931 |  |
Cumulative Paid Losses and ALAE | 2,377 | 2,303 | [1] | 2,140 | 1,998 | 1,765 | 1,359 | 908 | 373 |  |
IBNR and Case Development Liabilities | $ 361 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 125 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 3,321 | 3,320 | [1] | 3,322 | 3,310 | 3,299 | 3,337 | 3,473 |  |  |
Cumulative Paid Losses and ALAE | 2,673 | 2,492 | [1] | 2,279 | 2,050 | 1,645 | 1,133 | 480 |  |  |
IBNR and Case Development Liabilities | $ 422 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 143 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 4,177 | 4,091 | [1] | 4,030 | 3,967 | 3,886 | 3,998 |  |  |  |
Cumulative Paid Losses and ALAE | 3,120 | 2,746 | [1] | 2,324 | 1,902 | 1,340 | 583 |  |  |  |
IBNR and Case Development Liabilities | $ 643 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 163 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 4,847 | 4,763 | [1] | 4,692 | 4,623 | 4,584 |  |  |  |  |
Cumulative Paid Losses and ALAE | 3,430 | 2,898 | [1] | 2,214 | 1,598 | 725 |  |  |  |  |
IBNR and Case Development Liabilities | $ 867 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 184 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 4,774 | 4,775 | [1] | 4,881 | 5,030 |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 2,598 | 2,066 | [1] | 1,498 | 736 |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 1,467 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 156 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 5,882 | 5,856 | [1] | 5,899 |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 2,440 | 1,751 | [1] | 869 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 2,455 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 316 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 6,757 | 6,796 | [1] |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 2,012 | 962 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 3,646 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 308 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | $ 7,299 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 1,056 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | $ 5,187 |  |  |  |  |  |  |  |  |  |
Cumulative Number of Reported Claims | Claim | 132 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Before 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | $ 587 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Short Duration Insurance Contracts Accident Years 2014 Through 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 20,643 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 55,885 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 39,855 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 16,499 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 2,376 | 2,373 | [1] | 2,393 | 2,400 | 2,432 | 2,508 | 2,567 | 2,725 | 2,849 | 3,095
Cumulative Paid Losses and ALAE | 2,295 | 2,272 | [1] | 2,242 | 2,218 | 2,187 | 2,135 | 2,059 | 1,899 | 1,520 | 572
IBNR and Case Development Liabilities | 27 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 3,272 | 3,248 | [1] | 3,255 | 3,253 | 3,232 | 3,237 | 2,847 | 3,414 | 3,605 |
Cumulative Paid Losses and ALAE | 2,933 | 2,860 | [1] | 2,807 | 2,721 | 2,538 | 2,429 | 2,210 | 1,804 | 671 |
IBNR and Case Development Liabilities | 60 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 4,106 | 4,117 | [1] | 4,139 | 4,150 | 4,155 | 4,192 | 4,515 | 3,926 |  |
Cumulative Paid Losses and ALAE | 3,820 | 3,741 | [1] | 3,632 | 3,436 | 3,167 | 2,677 | 2,214 | 915 |  |
IBNR and Case Development Liabilities | 26 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 5,612 | 5,631 | [1] | 5,713 | 5,791 | 5,918 | 6,096 | 6,397 |  |  |
Cumulative Paid Losses and ALAE | 5,454 | 5,364 | [1] | 5,171 | 4,936 | 4,583 | 3,508 | 1,348 |  |  |
IBNR and Case Development Liabilities | 64 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 5,249 | 5,299 | [1] | 5,293 | 5,437 | 5,579 | 5,486 |  |  |  |
Cumulative Paid Losses and ALAE | 4,473 | 4,265 | [1] | 4,020 | 3,735 | 3,093 | 1,208 |  |  |  |
IBNR and Case Development Liabilities | 172 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 4,527 | 4,574 | [1] | 4,901 | 5,129 | 4,986 |  |  |  |  |
Cumulative Paid Losses and ALAE | 4,058 | 3,898 | [1] | 3,566 | 2,848 | 1,012 |  |  |  |  |
IBNR and Case Development Liabilities | 162 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 6,657 | 6,876 | [1] | 7,208 | 6,928 |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 5,298 | 4,634 | [1] | 3,584 | 1,255 |  |  |  |  |  |
IBNR and Case Development Liabilities | 610 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 7,640 | 7,976 | [1] | 8,103 |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 5,414 | 4,095 | [1] | 1,624 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 896 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 8,453 | 8,880 | [1] |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 4,333 | 1,814 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 2,228 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 7,993 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 1,777 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 4,140 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Before 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 469 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Short Duration Insurance Contracts Accident Years 2014 Through 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 16,030 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 49,870 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 27,044 |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | 32,393 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 3,265 | 3,298 | [1] | 3,334 | 3,446 | 3,472 | 3,456 | 3,557 | 3,619 | 3,672 | 3,507
Cumulative Paid Losses and ALAE | 2,560 | 2,493 | [1] | 2,405 | 2,311 | 2,103 | 1,917 | 1,662 | 1,390 | 1,002 | $ 429
IBNR and Case Development Liabilities | 424 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 3,312 | 3,310 | [1] | 3,364 | 3,401 | 3,438 | 3,580 | 3,668 | 3,628 | 3,422 |
Cumulative Paid Losses and ALAE | 2,590 | 2,481 | [1] | 2,345 | 2,197 | 2,003 | 1,731 | 1,431 | 995 | $ 446 |
IBNR and Case Development Liabilities | 373 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 3,773 | 3,746 | [1] | 3,775 | 3,819 | 3,870 | 3,902 | 3,998 | 3,788 |  |
Cumulative Paid Losses and ALAE | 2,963 | 2,789 | [1] | 2,613 | 2,420 | 2,149 | 1,801 | 1,359 | $ 654 |  |
IBNR and Case Development Liabilities | 416 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2017 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 4,222 | 4,165 | [1] | 4,176 | 4,244 | 4,351 | 4,474 | 4,039 |  |  |
Cumulative Paid Losses and ALAE | 3,171 | 2,945 | [1] | 2,727 | 2,478 | 1,829 | 1,311 | $ 607 |  |  |
IBNR and Case Development Liabilities | 547 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2018 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 5,370 | 5,285 | [1] | 5,358 | 5,489 | 5,537 | 4,886 |  |  |  |
Cumulative Paid Losses and ALAE | 3,954 | 3,637 | [1] | 3,258 | 2,792 | 1,742 | $ 695 |  |  |  |
IBNR and Case Development Liabilities | 756 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 5,695 | 5,736 | [1] | 5,902 | 6,043 | 5,572 |  |  |  |  |
Cumulative Paid Losses and ALAE | 3,736 | 3,190 | [1] | 2,423 | 1,872 | $ 841 |  |  |  |  |
IBNR and Case Development Liabilities | 1,228 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 6,093 | 6,047 | [1] | 6,231 | 6,214 |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 3,379 | 2,715 | [1] | 1,905 | $ 868 |  |  |  |  |  |
IBNR and Case Development Liabilities | 1,750 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2021 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 5,957 | 6,285 | [1] | 6,310 |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 2,661 | 1,785 | [1] | $ 766 |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 2,299 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2022 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 6,112 | 6,061 | [1] |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 1,338 | $ 622 | [1] |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 3,505 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Incurred Losses and ALAE | 6,071 |  |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and ALAE | 692 |  |  |  |  |  |  |  |  |  |
IBNR and Case Development Liabilities | 4,656 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Before 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net unpaid losses and ALAE for accident years before earliest accident year presented | 9,567 |  |  |  |  |  |  |  |  |  |
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Short Duration Insurance Contracts Accident Years 2014 Through 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unpaid losses and ALAE, net | $ 22,826 |  |  |  |  |  |  |  |  |  |
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