Business segment data - Additional tabular disclosures (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Interest expense		$ 5,394	$ 3,497	$ 3,515
Income tax expense		(21,515)	9,240	10,532
Income tax net benefit - Tax Cuts and Jobs Act of 2017	$ (28,200)	(28,200)
Capital expenditures		11,708	12,954	16,082
Depreciation of tangible assets		7,719	7,411	6,673
Goodwill at year-end	81,258	81,258	79,486	62,708
Total assets	702,095	702,095	620,854	552,257
Operating Businesses [Member]
Segment Reporting Information [Line Items]
Interest expense		3,931	3,332	3,245
Income tax expense		6,190	7,597	7,554
Capital expenditures		11,708	12,954	16,082
Depreciation of tangible assets		7,719	7,411	6,673
Goodwill at year-end	81,258	81,258	79,486
Identifiable assets at year-end	584,008	584,008	513,317	454,217
Operating Businesses [Member] | Insurance Group [Member]
Segment Reporting Information [Line Items]
Income tax expense		(55)	1,585	1,475
Capital expenditures		170	128	115
Depreciation of tangible assets		84	85	77
Goodwill at year-end	15,499	15,499	15,474
Identifiable assets at year-end	297,048	297,048	234,037	219,451
Operating Businesses [Member] | BNSF [Member]
Segment Reporting Information [Line Items]
Interest expense		1,016	992	928
Income tax expense		2,369	2,124	2,527
Capital expenditures		3,256	3,819	5,651
Depreciation of tangible assets		2,304	2,079	1,932
Goodwill at year-end	14,845	14,845	14,845
Identifiable assets at year-end	69,438	69,438	69,277	66,613
Operating Businesses [Member] | Berkshire Hathaway Energy [Member]
Segment Reporting Information [Line Items]
Interest expense		2,254	1,715	1,830
Income tax expense		178	403	450
Capital expenditures		4,571	5,090	5,875
Depreciation of tangible assets		2,548	2,560	2,451
Goodwill at year-end	9,935	9,935	9,266
Identifiable assets at year-end	80,195	80,195	76,428	74,221
Operating Businesses [Member] | Manufacturing Businesses [Member]
Segment Reporting Information [Line Items]
Interest expense		189	164	50
Income tax expense		2,155	1,945	1,548
Capital expenditures		1,905	1,813	1,292
Depreciation of tangible assets		1,357	1,287	938
Goodwill at year-end	32,981	32,981	32,041
Identifiable assets at year-end	72,630	72,630	69,900	34,141
Operating Businesses [Member] | McLane Company [Member]
Segment Reporting Information [Line Items]
Interest expense		19		13
Income tax expense		94	169	195
Capital expenditures		289	258	338
Depreciation of tangible assets		193	165	161
Goodwill at year-end	734	734	734
Identifiable assets at year-end	6,090	6,090	5,896	5,871
Operating Businesses [Member] | Service and Retailing Businesses [Member]
Segment Reporting Information [Line Items]
Interest expense		56	50	40
Income tax expense		726	669	651
Capital expenditures		587	804	574
Depreciation of tangible assets		583	611	504
Goodwill at year-end	5,771	5,771	5,745
Identifiable assets at year-end	18,215	18,215	17,450	16,299
Operating Businesses [Member] | Finance and Financial Products Reportable Segment [Member]
Segment Reporting Information [Line Items]
Interest expense		397	411	384
Income tax expense		723	702	708
Capital expenditures		930	1,042	2,237
Depreciation of tangible assets		650	624	610
Goodwill at year-end	1,493	1,493	1,381
Identifiable assets at year-end	40,392	40,392	40,329	37,621
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Interest expense		1,494	230	374
Investment and derivative gains/losses, tax		742	1,807	3,622
Interest expense, tax		(523)	(81)	(131)
Income tax net benefit - Tax Cuts and Jobs Act of 2017		(28,200)
Goodwill at year-end	81,258	81,258	79,486	62,708
Segment Reconciling Items [Member] | Kraft Heinz (previously Heinz Holding) [Member]
Segment Reporting Information [Line Items]
Investments in Kraft Heinz, tax		832	397	(111)
Corporate, Eliminations and Other [Member]
Segment Reporting Information [Line Items]
Interest expense		(31)	(65)	(104)
Income tax expense		(556)	(480)	(402)
Identifiable assets at year-end	$ 36,829	$ 36,829	$ 28,051	$ 35,332