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]
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

[1] Unaudited required supplemental information