v3.25.4
Unpaid losses and loss adjustment expenses - Losses and allocated loss adjustment expenses Incurred (Detail) - Insurance Group [Member]
Claim in Thousands, $ in Millions
Dec. 31, 2025
USD ($)
Claim
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Claims Development [Line Items]                    
Unpaid losses and ALAE, net $ 110,555                  
GEICO [Member] | Physical Damage [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 21,445                  
Cumulative Losses and ALAE Paid 20,664                  
Unpaid losses and ALAE, net 914                  
GEICO [Member] | Physical Damage [Member] | 2024 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 10,833 $ 11,095                
Cumulative Losses and ALAE Paid 10,728 10,495                
IBNR and Case Development Liabilities $ 88                  
Cumulative Number of Reported Claims | Claim 6,496                  
GEICO [Member] | Physical Damage [Member] | 2025 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 10,612                  
Cumulative Losses and ALAE Paid 9,936                  
IBNR and Case Development Liabilities $ (275)                  
Cumulative Number of Reported Claims | Claim 5,828                  
GEICO [Member] | Physical Damage [Member] | 2024-2025 [Member]                    
Claims Development [Line Items]                    
Unpaid losses and ALAE, net $ 781                  
GEICO [Member] | Physical Damage [Member] | Before 2024 [Member]                    
Claims Development [Line Items]                    
Net unpaid losses and ALAE for accident years before earliest accident year presented 133                  
GEICO [Member] | Auto Liability [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 90,445                  
Cumulative Losses and ALAE Paid 67,894                  
Unpaid losses and ALAE, net 23,526                  
GEICO [Member] | Auto Liability [Member] | 2021 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 16,827 17,033 [1] $ 17,229 [1] $ 17,457 [1] $ 17,481 [1]          
Cumulative Losses and ALAE Paid 16,132 15,796 [1] 14,863 [1] 12,681 [1] 6,450 [1]          
IBNR and Case Development Liabilities $ 545                  
Cumulative Number of Reported Claims | Claim 2,461                  
GEICO [Member] | Auto Liability [Member] | 2022 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 18,275 18,818 [1] 18,903 [1] 19,645 [1]            
Cumulative Losses and ALAE Paid 16,853 16,031 [1] 13,838 [1] 7,614 [1]            
IBNR and Case Development Liabilities $ 1,056                  
Cumulative Number of Reported Claims | Claim 2,397                  
GEICO [Member] | Auto Liability [Member] | 2023 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 17,234 18,073 [1] 17,948 [1]              
Cumulative Losses and ALAE Paid 14,555 12,682 [1] 7,191 [1]              
IBNR and Case Development Liabilities $ 1,856                  
Cumulative Number of Reported Claims | Claim 1,977                  
GEICO [Member] | Auto Liability [Member] | 2024 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 18,208 17,081 [1]                
Cumulative Losses and ALAE Paid 12,764 7,084 [1]                
IBNR and Case Development Liabilities $ 3,361                  
Cumulative Number of Reported Claims | Claim 1,842                  
GEICO [Member] | Auto Liability [Member] | 2025 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 19,901                  
Cumulative Losses and ALAE Paid 7,590                  
IBNR and Case Development Liabilities $ 5,897                  
Cumulative Number of Reported Claims | Claim 1,742                  
GEICO [Member] | Auto Liability [Member] | 2021-2025 [Member]                    
Claims Development [Line Items]                    
Unpaid losses and ALAE, net $ 22,551                  
GEICO [Member] | Auto Liability [Member] | Before 2021 [Member]                    
Claims Development [Line Items]                    
Net unpaid losses and ALAE for accident years before earliest accident year presented 975                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 16,755                  
Cumulative Losses and ALAE Paid 7,507                  
Unpaid losses and ALAE, net 9,721                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2016 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 1,184 1,172 [1] 1,188 [1] 1,216 [1] 1,288 [1] $ 1,341 [1] $ 1,394 [1] $ 1,414 [1] $ 1,416 [1] $ 1,392 [1]
Cumulative Losses and ALAE Paid 1,022 957 [1] 908 [1] 822 [1] 712 [1] 620 [1] 461 [1] 274 [1] 115 [1] 22 [1]
IBNR and Case Development Liabilities $ 64                  
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 $ 1,321 1,310 [1] 1,315 [1] 1,349 [1] 1,382 [1] 1,474 [1] 1,495 [1] 1,499 [1] 1,466 [1]  
Cumulative Losses and ALAE Paid 1,051 977 [1] 877 [1] 739 [1] 582 [1] 457 [1] 300 [1] 128 [1] 27 [1]  
IBNR and Case Development Liabilities $ 86                  
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 $ 1,580 1,583 [1] 1,606 [1] 1,616 [1] 1,580 [1] 1,659 [1] 1,650 [1] 1,602 [1]    
Cumulative Losses and ALAE Paid 1,209 1,080 [1] 949 [1] 728 [1] 543 [1] 367 [1] 166 [1] 35 [1]    
IBNR and Case Development Liabilities $ 115                  
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 $ 1,608 1,579 [1] 1,534 [1] 1,614 [1] 1,663 [1] 1,691 [1] 1,670 [1]      
Cumulative Losses and ALAE Paid 1,154 963 [1] 757 [1] 536 [1] 314 [1] 160 [1] 39 [1]      
IBNR and Case Development Liabilities $ 129                  
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 $ 1,584 1,606 [1] 1,631 [1] 1,698 [1] 1,751 [1] 1,704 [1]        
Cumulative Losses and ALAE Paid 976 767 [1] 531 [1] 321 [1] 148 [1] 34 [1]        
IBNR and Case Development Liabilities $ 225                  
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 $ 1,671 1,714 [1] 1,787 [1] 1,855 [1] 1,852 [1]          
Cumulative Losses and ALAE Paid 787 548 [1] 333 [1] 136 [1] 36 [1]          
IBNR and Case Development Liabilities $ 452                  
Cumulative Number of Reported Claims | Claim 26                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2022 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 1,814 1,846 [1] 1,912 [1] 1,927 [1]            
Cumulative Losses and ALAE Paid 700 441 [1] 182 [1] 38 [1]            
IBNR and Case Development Liabilities $ 650                  
Cumulative Number of Reported Claims | Claim 24                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2023 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 1,892 1,918 [1] 1,964 [1]              
Cumulative Losses and ALAE Paid 404 156 [1] 28 [1]              
IBNR and Case Development Liabilities $ 1,052                  
Cumulative Number of Reported Claims | Claim 26                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2024 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 2,116 2,004 [1]                
Cumulative Losses and ALAE Paid 178 34 [1]                
IBNR and Case Development Liabilities $ 1,533                  
Cumulative Number of Reported Claims | Claim 29                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2025 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 1,985                  
Cumulative Losses and ALAE Paid 26                  
IBNR and Case Development Liabilities $ 1,803                  
Cumulative Number of Reported Claims | Claim 13                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Short Duration Insurance Contracts Accident Years 2016 Through 2025 [Member]                    
Claims Development [Line Items]                    
Unpaid losses and ALAE, net $ 9,248                  
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Before 2016 [Member]                    
Claims Development [Line Items]                    
Net unpaid losses and ALAE for accident years before earliest accident year presented 473                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 56,845                  
Cumulative Losses and ALAE Paid 30,800                  
Unpaid losses and ALAE, net 26,912                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2016 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 2,802 2,809 [2] 2,840 [2] 2,864 [2] 2,825 [2] 2,815 [2] 2,772 [2] 2,793 [2] 2,848 [2] 2,931 [2]
Cumulative Losses and ALAE Paid 2,468 2,420 [2] 2,377 [2] 2,303 [2] 2,140 [2] 1,998 [2] 1,765 [2] 1,359 [2] 908 [2] 373 [2]
IBNR and Case Development Liabilities $ 226                  
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 $ 3,385 3,357 [2] 3,321 [2] 3,320 [2] 3,322 [2] 3,310 [2] 3,299 [2] 3,337 [2] 3,473 [2]  
Cumulative Losses and ALAE Paid 2,871 2,784 [2] 2,673 [2] 2,492 [2] 2,279 [2] 2,050 [2] 1,645 [2] 1,133 [2] 480 [2]  
IBNR and Case Development Liabilities $ 338                  
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 $ 4,205 4,230 [2] 4,177 [2] 4,091 [2] 4,030 [2] 3,967 [2] 3,886 [2] 3,998 [2]    
Cumulative Losses and ALAE Paid 3,517 3,396 [2] 3,120 [2] 2,746 [2] 2,324 [2] 1,902 [2] 1,340 [2] 583 [2]    
IBNR and Case Development Liabilities $ 480                  
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 $ 4,935 4,919 [2] 4,847 [2] 4,763 [2] 4,692 [2] 4,623 [2] 4,584 [2]      
Cumulative Losses and ALAE Paid 4,015 3,812 [2] 3,430 [2] 2,898 [2] 2,214 [2] 1,598 [2] 725 [2]      
IBNR and Case Development Liabilities $ 599                  
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 $ 4,918 4,866 [2] 4,774 [2] 4,775 [2] 4,881 [2] 5,030 [2]        
Cumulative Losses and ALAE Paid 3,474 3,138 [2] 2,598 [2] 2,066 [2] 1,498 [2] 736 [2]        
IBNR and Case Development Liabilities $ 1,019                  
Cumulative Number of Reported Claims | Claim 159                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2021 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 6,200 5,976 [2] 5,875 [2] 5,847 [2] 5,890 [2]          
Cumulative Losses and ALAE Paid 3,797 3,161 [2] 2,433 [2] 1,744 [2] 865 [2]          
IBNR and Case Development Liabilities $ 1,493                  
Cumulative Number of Reported Claims | Claim 167                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2022 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 6,966 6,862 [2] 6,753 [2] 6,781 [2]            
Cumulative Losses and ALAE Paid 3,711 2,901 [2] 2,008 [2] 958 [2]            
IBNR and Case Development Liabilities $ 2,329                  
Cumulative Number of Reported Claims | Claim 190                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2023 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 7,514 7,363 [2] 7,299 [2]              
Cumulative Losses and ALAE Paid 3,230 2,152 [2] 1,056 [2]              
IBNR and Case Development Liabilities $ 2,974                  
Cumulative Number of Reported Claims | Claim 190                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2024 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 7,918 7,962 [2]                
Cumulative Losses and ALAE Paid 2,428 1,245 [2]                
IBNR and Case Development Liabilities $ 4,169                  
Cumulative Number of Reported Claims | Claim 184                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2025 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred $ 8,002                  
Cumulative Losses and ALAE Paid 1,289                  
IBNR and Case Development Liabilities $ 5,548                  
Cumulative Number of Reported Claims | Claim 141                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Short Duration Insurance Contracts Accident Years 2016 Through 2025 [Member]                    
Claims Development [Line Items]                    
Unpaid losses and ALAE, net $ 26,045                  
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Before 2016 [Member]                    
Claims Development [Line Items]                    
Net unpaid losses and ALAE for accident years before earliest accident year presented 867                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 61,864                  
Cumulative Losses and ALAE Paid 47,603                  
Unpaid losses and ALAE, net 14,944                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2016 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 4,120 4,131 [3] 4,127 [3] 4,138 [3] 4,161 [3] 4,172 [3] 4,177 [3] 4,216 [3] 4,542 [3] 3,953 [3]
Cumulative Losses and ALAE Paid 3,965 3,927 [3] 3,840 [3] 3,761 [3] 3,652 [3] 3,456 [3] 3,187 [3] 2,695 [3] 2,228 [3] 918 [3]
IBNR and Case Development Liabilities 17                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2017 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 5,613 5,616 [3] 5,630 [3] 5,649 [3] 5,731 [3] 5,810 [3] 5,938 [3] 6,117 [3] 6,420 [3]  
Cumulative Losses and ALAE Paid 5,529 5,494 [3] 5,470 [3] 5,380 [3] 5,187 [3] 4,951 [3] 4,597 [3] 3,517 [3] 1,350 [3]  
IBNR and Case Development Liabilities 42                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2018 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 5,288 5,298 [3] 5,278 [3] 5,329 [3] 5,324 [3] 5,470 [3] 5,612 [3] 5,514 [3]    
Cumulative Losses and ALAE Paid 4,734 4,627 [3] 4,500 [3] 4,291 [3] 4,045 [3] 3,757 [3] 3,108 [3] 1,211 [3]    
IBNR and Case Development Liabilities 168                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2019 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 4,520 4,508 [3] 4,545 [3] 4,601 [3] 4,906 [3] 5,134 [3] 5,002 [3]      
Cumulative Losses and ALAE Paid 4,223 4,136 [3] 4,066 [3] 3,907 [3] 3,577 [3] 2,855 [3] 1,014 [3]      
IBNR and Case Development Liabilities 128                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2020 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,469 6,525 [3] 6,698 [3] 6,907 [3] 7,273 [3] 6,992 [3]        
Cumulative Losses and ALAE Paid 5,797 5,605 [3] 5,327 [3] 4,659 [3] 3,600 [3] 1,259 [3]        
IBNR and Case Development Liabilities 280                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2021 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 7,212 7,398 [3] 7,702 [3] 8,040 [3] 8,157 [3]          
Cumulative Losses and ALAE Paid 6,526 6,160 [3] 5,455 [3] 4,121 [3] 1,630 [3]          
IBNR and Case Development Liabilities 269                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2022 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 7,992 7,986 [3] 8,485 [3] 8,912 [3]            
Cumulative Losses and ALAE Paid 6,518 5,631 [3] 4,352 [3] 1,817 [3]            
IBNR and Case Development Liabilities 709                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2023 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,963 7,471 [3] 8,038 [3]              
Cumulative Losses and ALAE Paid 5,174 4,148 [3] 1,773 [3]              
IBNR and Case Development Liabilities 951                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2024 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 7,108 7,838 [3]                
Cumulative Losses and ALAE Paid 3,595 1,725 [3]                
IBNR and Case Development Liabilities 2,008                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2025 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,579                  
Cumulative Losses and ALAE Paid 1,542                  
IBNR and Case Development Liabilities 3,325                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Short Duration Insurance Contracts Accident Years 2016 Through 2025 [Member]                    
Claims Development [Line Items]                    
Unpaid losses and ALAE, net 14,261                  
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Before 2016 [Member]                    
Claims Development [Line Items]                    
Unpaid losses and ALAE, net 683                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 56,512                  
Cumulative Losses and ALAE Paid 31,601                  
Unpaid losses and ALAE, net 34,538                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2016 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 3,834 3,828 [4] 3,797 [4] 3,771 [4] 3,800 [4] 3,844 [4] 3,897 [4] 3,931 [4] 4,026 [4] 3,811 [4]
Cumulative Losses and ALAE Paid 3,235 3,144 [4] 3,007 [4] 2,828 [4] 2,654 [4] 2,450 [4] 2,174 [4] 1,809 [4] 1,366 [4] $ 656 [4]
IBNR and Case Development Liabilities 328                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2017 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 4,307 4,253 [4] 4,252 [4] 4,195 [4] 4,206 [4] 4,274 [4] 4,382 [4] 4,507 [4] 4,063 [4]  
Cumulative Losses and ALAE Paid 3,535 3,374 [4] 3,187 [4] 2,959 [4] 2,740 [4] 2,490 [4] 1,839 [4] 1,319 [4] $ 609 [4]  
IBNR and Case Development Liabilities 406                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2018 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 5,593 5,469 [4] 5,396 [4] 5,310 [4] 5,384 [4] 5,516 [4] 5,577 [4] 4,917 [4]    
Cumulative Losses and ALAE Paid 4,484 4,251 [4] 3,973 [4] 3,654 [4] 3,273 [4] 2,803 [4] 1,750 [4] $ 697 [4]    
IBNR and Case Development Liabilities 632                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2019 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 5,918 5,822 [4] 5,748 [4] 5,789 [4] 5,961 [4] 6,090 [4] 5,606 [4]      
Cumulative Losses and ALAE Paid 4,496 4,127 [4] 3,759 [4] 3,207 [4] 2,447 [4] 1,886 [4] $ 844 [4]      
IBNR and Case Development Liabilities 866                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2020 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,126 6,115 [4] 6,140 [4] 6,096 [4] 6,277 [4] 6,248 [4]        
Cumulative Losses and ALAE Paid 4,427 3,986 [4] 3,388 [4] 2,723 [4] 1,909 [4] $ 871 [4]        
IBNR and Case Development Liabilities 1,104                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2021 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,014 5,997 [4] 5,979 [4] 6,309 [4] 6,324 [4]          
Cumulative Losses and ALAE Paid 3,840 3,242 [4] 2,674 [4] 1,790 [4] $ 778 [4]          
IBNR and Case Development Liabilities 1,449                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2022 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,217 6,085 [4] 6,132 [4] 6,078 [4]            
Cumulative Losses and ALAE Paid 2,853 1,977 [4] 1,343 [4] $ 623 [4]            
IBNR and Case Development Liabilities 2,181                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2023 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,123 6,189 [4] 6,088 [4]              
Cumulative Losses and ALAE Paid 2,380 1,590 [4] $ 694 [4]              
IBNR and Case Development Liabilities 2,696                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2024 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,233 6,123 [4]                
Cumulative Losses and ALAE Paid 1,647 $ 682 [4]                
IBNR and Case Development Liabilities 3,628                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2025 [Member]                    
Claims Development [Line Items]                    
Losses and ALAE incurred 6,147                  
Cumulative Losses and ALAE Paid 704                  
IBNR and Case Development Liabilities 4,678                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Short Duration Insurance Contracts Accident Years 2016 Through 2025 [Member]                    
Claims Development [Line Items]                    
Unpaid losses and ALAE, net 24,911                  
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Before 2016 [Member]                    
Claims Development [Line Items]                    
Net unpaid losses and ALAE for accident years before earliest accident year presented $ 9,627                  
[1] Unaudited required supplemental information
[2] Unaudited required supplemental information
[3] Unaudited required supplemental information
[4] Unaudited required supplemental information