Business segment data - Additional tabular disclosures (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Interest expense		$ 3,853	$ 4,386	$ 3,741
Income tax expense		(321)	(21,515)	9,240
Income tax net benefit - Tax Cuts and Jobs Act of 2017	$ (28,200)		(28,200)
Capital expenditures		14,537	11,708	12,954
Depreciation of tangible assets		7,284	6,968	6,656
Goodwill at year-end	81,258	81,025	81,258	79,486
Total assets	702,095	707,794	702,095	620,854
Operating Businesses [Member]
Segment Reporting Information [Line Items]
Interest expense		3,614	4,035	3,409
Income tax expense		5,447	6,030	7,452
Capital expenditures		14,537	11,708	12,954
Depreciation of tangible assets		8,386	7,719	7,411
Goodwill at year-end	81,258	81,025	81,258	79,486
Identifiable assets at year-end	565,423	571,410	565,423	496,824
Operating Businesses [Member] | Insurance Group [Member]
Segment Reporting Information [Line Items]
Income tax expense		1,374	(71)	1,585
Capital expenditures		130	170	128
Depreciation of tangible assets		79	84	85
Goodwill at year-end	15,499	15,289	15,499	15,474
Identifiable assets at year-end	294,418	289,746	294,418	234,037
Operating Businesses [Member] | BNSF [Member]
Segment Reporting Information [Line Items]
Interest expense		1,041	1,016	992
Income tax expense		1,644	2,369	2,124
Capital expenditures		3,187	3,256	3,819
Depreciation of tangible assets		2,268	2,304	2,079
Goodwill at year-end	14,845	14,851	14,845	14,845
Identifiable assets at year-end	69,438	70,242	69,438	69,277
Operating Businesses [Member] | Berkshire Hathaway Energy [Member]
Segment Reporting Information [Line Items]
Interest expense		1,777	2,254	1,715
Income tax expense		(452)	148	371
Capital expenditures		6,241	4,571	5,090
Depreciation of tangible assets		2,830	2,548	2,560
Goodwill at year-end	9,935	9,851	9,935	9,266
Identifiable assets at year-end	77,710	80,543	77,710	74,571
Operating Businesses [Member] | Manufacturing Businesses [Member]
Segment Reporting Information [Line Items]
Interest expense		690	679	631
Income tax expense		2,188	2,678	2,442
Capital expenditures		3,116	2,490	2,581
Depreciation of tangible assets		1,890	1,839	1,757
Goodwill at year-end	33,967	34,019	33,967	32,915
Identifiable assets at year-end	97,753	99,912	97,753	93,835
Operating Businesses [Member] | McLane Company [Member]
Segment Reporting Information [Line Items]
Interest expense		15	19
Income tax expense		59	94	169
Capital expenditures		276	289	258
Depreciation of tangible assets		204	193	165
Goodwill at year-end	734	734	734	734
Identifiable assets at year-end	6,090	6,243	6,090	5,896
Operating Businesses [Member] | Service and Retailing Businesses [Member]
Segment Reporting Information [Line Items]
Interest expense		91	67	71
Income tax expense		634	812	761
Capital expenditures		1,587	932	1,078
Depreciation of tangible assets		1,115	751	765
Goodwill at year-end	6,278	6,281	6,278	6,252
Identifiable assets at year-end	20,014	24,724	20,014	19,208
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Interest expense		458	486	474
Investment and derivative gains/losses, tax		(4,673)	742	1,807
Interest expense, tax		(96)	(170)	(166)
Equity method investments, tax		(753)	910	396
Income tax net benefit - Tax Cuts and Jobs Act of 2017			(28,200)
Goodwill at year-end	81,258	81,025	81,258	79,486
Corporate, Eliminations and Other [Member]
Segment Reporting Information [Line Items]
Interest expense		(219)	(135)	(142)
Income tax expense		(246)	(827)	(249)
Identifiable assets at year-end	$ 55,414	$ 55,359	$ 55,414	$ 44,544