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, 2021 USD ($) Claim	Dec. 31, 2020 USD ($)	[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]	Dec. 31, 2013 USD ($)	[1]	Dec. 31, 2012 USD ($)	[1]
Claims Development [Line Items]
Unpaid losses and ALAE, net	$ 79,312
GEICO [Member] | Physical Damage [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	20,531
Cumulative Paid Losses and ALAE	19,812
Unpaid losses and ALAE, net	729
GEICO [Member] | Physical Damage [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	8,396	$ 8,603
Cumulative Paid Losses and ALAE	8,385	8,118
IBNR and Case Development Liabilities	$ 64
Cumulative Number of Reported Claims | Claim	7,935
GEICO [Member] | Physical Damage [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 12,135
Cumulative Paid Losses and ALAE	11,427
IBNR and Case Development Liabilities	$ 420
Cumulative Number of Reported Claims | Claim	8,967
GEICO [Member] | Physical Damage [Member] | 2020-2021 [Member]
Claims Development [Line Items]
Unpaid losses and ALAE, net	$ 719
GEICO [Member] | Physical Damage [Member] | Shortduration Insurance Contracts Accident Years Before 2020
Claims Development [Line Items]
Net unpaid losses and ALAE for accident years before earliest accident year presented	10
GEICO [Member] | Auto Liability [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	76,311
Cumulative Paid Losses and ALAE	57,157
Unpaid losses and ALAE, net	19,768
GEICO [Member] | Auto Liability [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	13,777	13,824		$ 13,888		$ 13,864		$ 14,095
Cumulative Paid Losses and ALAE	13,260	12,729		11,799		9,944		5,806
IBNR and Case Development Liabilities	$ 232
Cumulative Number of Reported Claims | Claim	2,646
GEICO [Member] | Auto Liability [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 14,024	14,637
Cumulative Paid Losses and ALAE	9,839	5,395
IBNR and Case Development Liabilities	$ 2,564
Cumulative Number of Reported Claims | Claim	2,087
GEICO [Member] | Auto Liability [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 17,481
Cumulative Paid Losses and ALAE	6,450
IBNR and Case Development Liabilities	$ 5,541
Cumulative Number of Reported Claims | Claim	2,216
GEICO [Member] | Auto Liability [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 14,838	14,985		15,226		15,383
Cumulative Paid Losses and ALAE	13,757	12,658		10,772		6,218
IBNR and Case Development Liabilities	$ 495
Cumulative Number of Reported Claims | Claim	2,713
GEICO [Member] | Auto Liability [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 16,191	16,678		16,901
Cumulative Paid Losses and ALAE	13,851	11,671		6,742
IBNR and Case Development Liabilities	$ 1,202
Cumulative Number of Reported Claims | Claim	2,778
GEICO [Member] | Auto Liability [Member] | 2017-2021 [Member]
Claims Development [Line Items]
Unpaid losses and ALAE, net	$ 19,154
GEICO [Member] | Auto Liability [Member] | Before 2017 [Member]
Claims Development [Line Items]
Net unpaid losses and ALAE for accident years before earliest accident year presented	614
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	13,591
Cumulative Paid Losses and ALAE	5,511
Unpaid losses and ALAE, net	8,506
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2012 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	971	988		998		1,035		1,078		$ 1,168		$ 1,223		$ 1,277		$ 1,306		$ 1,336
Cumulative Paid Losses and ALAE	848	830		789		725		642		522		377		218		93		15
IBNR and Case Development Liabilities	$ 51
Cumulative Number of Reported Claims | Claim	11
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 978	985		1,019		1,086		1,127		1,195		1,261		1,296		1,328
Cumulative Paid Losses and ALAE	821	793		743		635		518		368		219		90		15
IBNR and Case Development Liabilities	$ 62
Cumulative Number of Reported Claims | Claim	11
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 1,033	1,061		1,127		1,218		1,246		1,305		1,375		1,370
Cumulative Paid Losses and ALAE	788	752		671		540		396		238		106		21
IBNR and Case Development Liabilities	$ 108
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	$ 1,093	1,157		1,218		1,290		1,269		1,342		1,374
Cumulative Paid Losses and ALAE	719	663		543		382		218		108		23
IBNR and Case Development Liabilities	$ 136
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	$ 1,288	1,341		1,394		1,414		1,416		1,392
Cumulative Paid Losses and ALAE	712	620		461		274		115		22
IBNR and Case Development Liabilities	$ 213
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	$ 1,382	1,474		1,495		1,499		1,466
Cumulative Paid Losses and ALAE	582	457		300		128		27
IBNR and Case Development Liabilities	$ 328
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	$ 1,751	1,704
Cumulative Paid Losses and ALAE	148	34
IBNR and Case Development Liabilities	$ 1,319
Cumulative Number of Reported Claims | Claim	27
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 1,852
Cumulative Paid Losses and ALAE	36
IBNR and Case Development Liabilities	$ 1,672
Cumulative Number of Reported Claims | Claim	15
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 1,580	1,659		1,650		1,602
Cumulative Paid Losses and ALAE	543	367		166		35
IBNR and Case Development Liabilities	$ 495
Cumulative Number of Reported Claims | Claim	23
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 1,663	1,691		1,670
Cumulative Paid Losses and ALAE	314	160		39
IBNR and Case Development Liabilities	$ 869
Cumulative Number of Reported Claims | Claim	20
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Shortduration Insurance Contracts Accident Years 2012 Through 2021
Claims Development [Line Items]
Unpaid losses and ALAE, net	$ 8,080
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] | Shortduration Insurance Contracts Accident Years Before 2012
Claims Development [Line Items]
Net unpaid losses and ALAE for accident years before earliest accident year presented	426
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	27,591
Cumulative Paid Losses and ALAE	14,425
Unpaid losses and ALAE, net	13,579
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2012 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	709	718		736		750		762		780		791		837		850		873
Cumulative Paid Losses and ALAE	640	634		626		611		592		560		501		414		299		116
IBNR and Case Development Liabilities	$ 39
Cumulative Number of Reported Claims | Claim	53
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 1,008	1,028		1,050		1,072		1,096		1,127		1,178		1,228		1,258
Cumulative Paid Losses and ALAE	884	874		858		835		793		725		609		422		177
IBNR and Case Development Liabilities	$ 96
Cumulative Number of Reported Claims | Claim	67
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 1,460	1,477		1,497		1,482		1,548		1,614		1,638		1,743
Cumulative Paid Losses and ALAE	1,245	1,214		1,176		1,111		1,007		800		557		239
IBNR and Case Development Liabilities	$ 163
Cumulative Number of Reported Claims | Claim	90
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2015 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 2,006	1,997		2,025		2,014		2,042		2,127		2,169
Cumulative Paid Losses and ALAE	1,648	1,570		1,488		1,289		1,017		700		289
IBNR and Case Development Liabilities	$ 242
Cumulative Number of Reported Claims | Claim	111
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 2,370	2,365		2,325		2,359		2,422		2,511
Cumulative Paid Losses and ALAE	1,778	1,661		1,461		1,148		775		329
IBNR and Case Development Liabilities	$ 396
Cumulative Number of Reported Claims | Claim	115
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 2,852	2,843		2,842		2,907		3,044
Cumulative Paid Losses and ALAE	1,956	1,771		1,434		1,003		441
IBNR and Case Development Liabilities	$ 503
Cumulative Number of Reported Claims | Claim	139
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 4,278	4,421
Cumulative Paid Losses and ALAE	1,391	695
IBNR and Case Development Liabilities	$ 2,089
Cumulative Number of Reported Claims | Claim	141
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 5,197
Cumulative Paid Losses and ALAE	833
IBNR and Case Development Liabilities	$ 3,545
Cumulative Number of Reported Claims | Claim	218
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 3,536	3,480		3,412		3,544
Cumulative Paid Losses and ALAE	2,028	1,683		1,198		538
IBNR and Case Development Liabilities	$ 908
Cumulative Number of Reported Claims | Claim	160
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	$ 4,175	4,102		4,074
Cumulative Paid Losses and ALAE	2,022	1,478		682
IBNR and Case Development Liabilities	$ 1,278
Cumulative Number of Reported Claims | Claim	173
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Shortduration Insurance Contracts Accident Years 2012 Through 2021
Claims Development [Line Items]
Unpaid losses and ALAE, net	$ 13,166
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] | Shortduration Insurance Contracts Accident Years Before 2012
Claims Development [Line Items]
Net unpaid losses and ALAE for accident years before earliest accident year presented	413
Berkshire Hathaway Reinsurance Group [Member] | Property [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	38,874
Cumulative Paid Losses and ALAE	26,156
Unpaid losses and ALAE, net	13,119
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2012 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	2,305	2,285		2,294		2,309		2,327		2,330		2,382		2,621		2,822		3,129
Cumulative Paid Losses and ALAE	2,201	2,180		2,162		2,117		2,097		2,022		1,934		1,796		1,218		259
IBNR and Case Development Liabilities	31
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	2,453	2,455		2,469		2,520		2,579		2,600		2,690		3,035		3,198
Cumulative Paid Losses and ALAE	2,352	2,328		2,300		2,260		2,180		2,060		1,863		1,424		515
IBNR and Case Development Liabilities	29
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	1,996	1,999		2,028		2,100		2,154		2,297		2,408		2,619
Cumulative Paid Losses and ALAE	1,860	1,838		1,808		1,758		1,693		1,555		1,234		465
IBNR and Case Development Liabilities	33
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2015 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	2,975	2,971		2,948		2,950		2,546		3,103		3,256
Cumulative Paid Losses and ALAE	2,510	2,427		2,245		2,141		1,946		1,596		577
IBNR and Case Development Liabilities	154
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	3,578	3,589		3,585		3,616		3,890		3,261
Cumulative Paid Losses and ALAE	3,083	2,899		2,647		2,186		1,794		705
IBNR and Case Development Liabilities	112
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	4,631	4,698		4,806		4,953		5,253
Cumulative Paid Losses and ALAE	4,163	3,944		3,633		2,712		1,025
IBNR and Case Development Liabilities	141
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	6,048	5,795
Cumulative Paid Losses and ALAE	2,882	956
IBNR and Case Development Liabilities	1,504
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	6,669
Cumulative Paid Losses and ALAE	1,214
IBNR and Case Development Liabilities	3,405
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	4,227	4,344		4,467		4,375
Cumulative Paid Losses and ALAE	3,061	2,831		2,310		907
IBNR and Case Development Liabilities	461
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	3,992	4,234		4,065
Cumulative Paid Losses and ALAE	2,830	2,247		748
IBNR and Case Development Liabilities	541
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Shortduration Insurance Contracts Accident Years 2012 Through 2021
Claims Development [Line Items]
Unpaid losses and ALAE, net	12,718
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] | Shortduration Insurance Contracts Accident Years Before 2012
Claims Development [Line Items]
Net unpaid losses and ALAE for accident years before earliest accident year presented	401
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	27,135
Cumulative Paid Losses and ALAE	12,212
Unpaid losses and ALAE, net	23,611
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2012 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	2,557	2,556		2,562		2,619		2,686		2,799		2,871		2,808		2,974		2,792
Cumulative Paid Losses and ALAE	1,906	1,868		1,810		1,750		1,650		1,525		1,368		1,139		747		$ 308
IBNR and Case Development Liabilities	372
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2013 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	1,837	1,865		1,937		2,032		2,086		2,141		2,298		2,268		2,132
Cumulative Paid Losses and ALAE	1,290	1,256		1,199		1,139		1,037		933		805		519		$ 290
IBNR and Case Development Liabilities	331
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2014 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	1,847	1,942		1,952		1,915		2,001		2,038		2,069		1,872
Cumulative Paid Losses and ALAE	1,147	1,103		959		874		752		642		477		$ 149
IBNR and Case Development Liabilities	431
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2015 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	1,817	1,844		1,882		2,008		2,109		2,082		1,877
Cumulative Paid Losses and ALAE	1,088	1,014		924		833		713		489		$ 196
IBNR and Case Development Liabilities	395
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	1,843	1,900		1,980		2,023		2,115		1,906
Cumulative Paid Losses and ALAE	1,043	960		862		732		555		$ 253
IBNR and Case Development Liabilities	451
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	2,383	2,470		2,563		2,685		2,193
Cumulative Paid Losses and ALAE	1,376	1,269		819		564		$ 230
IBNR and Case Development Liabilities	582
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	3,987	3,861
Cumulative Paid Losses and ALAE	970	404
IBNR and Case Development Liabilities	2,147
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	3,744
Cumulative Paid Losses and ALAE	307
IBNR and Case Development Liabilities	2,584
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	3,340	3,482		3,559		2,924
Cumulative Paid Losses and ALAE	1,909	1,639		867		$ 265
IBNR and Case Development Liabilities	904
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE	3,780	3,901		3,429
Cumulative Paid Losses and ALAE	1,176	$ 896		$ 353
IBNR and Case Development Liabilities	1,521
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Shortduration Insurance Contracts Accident Years 2012 Through 2021
Claims Development [Line Items]
Unpaid losses and ALAE, net	14,923
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] | Shortduration Insurance Contracts Accident Years Before 2012
Claims Development [Line Items]
Net unpaid losses and ALAE for accident years before earliest accident year presented	$ 8,688

[1] Unaudited required supplemental information