Property, plant and equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 42,210	$ 39,827
Property, plant and equipment, accumulated depreciation	(20,772)	(19,199)
Total property, plant and equipment, net	21,438	20,628
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,540	2,536
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,719	9,959
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	24,285	22,574
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,666	4,758
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	76,634	73,189
Property, plant and equipment, accumulated depreciation	(12,101)	(10,004)
Total property, plant and equipment, net	64,533	63,185
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	62,404	59,509
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,482	13,016
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	748	664
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	101,841	96,246
Property, plant and equipment, accumulated depreciation	(28,536)	(27,651)
Total property, plant and equipment, net	73,305	68,595
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	81,127	77,288
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,165	7,524
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,817	8,324
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,732	3,110
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 137,838	$ 131,780