Business segment data - Earnings (loss) before income taxes (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Investment and derivative gains (losses)	$ 10,926	$ 14,706	$ 41,296	$ 13,053
Equity method investments	644	316	936	1,044
Earnings (loss) before income taxes	20,489	23,147	65,895	36,722
Operating Businesses [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	8,538	8,212	23,443	22,971
Operating Businesses [Member] \| Insurance Group [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	2,363	2,054	6,440	6,373
Operating Businesses [Member] \| Insurance Group [Member] \| Interest, Dividend and Other Investment Income [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	1,782	1,455	4,916	4,052
Operating Businesses [Member] \| Insurance Group [Member] \| GEICO [Member] \| Insurance Premiums Earned [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	376	627	1,539	1,977
Operating Businesses [Member] \| Insurance Group [Member] \| Berkshire Hathaway Reinsurance Group [Member] \| Insurance Premiums Earned [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	52	(163)	(305)	(124)
Operating Businesses [Member] \| Insurance Group [Member] \| Berkshire Hathaway Primary Group [Member] \| Insurance Premiums Earned [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	153	135	290	468
Operating Businesses [Member] \| BNSF [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	1,941	1,879	5,379	5,047
Operating Businesses [Member] \| Berkshire Hathaway Energy [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	1,061	1,165	2,194	2,238
Operating Businesses [Member] \| Manufacturing Businesses [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	2,484	2,369	7,205	7,105
Operating Businesses [Member] \| McLane Company [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	50	44	220	171
Operating Businesses [Member] \| Service and Retailing Businesses [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	639	701	2,005	2,037
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Investment and derivative gains (losses)	10,926	14,706	41,296	13,053
Interest expense, not allocated to segments	(96)	(115)	(312)	(350)
Equity method investments	644	316	936	1,044
Corporate, Eliminations and Other [Member]
Segment Reporting Information [Line Items]
Earnings (loss) before income taxes from operating businesses	$ 477	$ 28	$ 532	$ 4

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(8))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

+ Details

Name:	us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of income (loss) for proportionate share of equity method investee's income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(13)(f))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

+ Details

Name:	us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (210.5-03(11))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.9)
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

+ Details

Name:	us-gaap_InterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

+ References

+ Details

Name:	us-gaap_NonoperatingIncomeExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_BerkshireHathawayInsuranceGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InvestmentIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=brka_GeicoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=brka_PremiumsEarnedNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=brka_BerkshireHathawayReinsuranceGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=brka_BerkshireHathawayPrimaryGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_BurlingtonNorthernSantaFeCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_BerkshireHathawayEnergyCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_ManufacturingBusinessesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_McLaneCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_ServiceAndRetailingBusinessesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_MaterialReconcilingItemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=brka_CorporateReconcilingItemsAndEliminationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: