Property, plant and equipment (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 41,560	$ 39,827
Property, plant and equipment, accumulated depreciation	(20,330)	(19,199)
Total property, plant and equipment, net	21,230	20,628
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,557	2,536
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,530	9,959
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	23,409	22,574
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,064	4,758
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	75,514	73,189
Property, plant and equipment, accumulated depreciation	(11,512)	(10,004)
Total property, plant and equipment, net	64,002	63,185
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	61,345	59,509
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,381	13,016
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	788	664
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	100,118	96,246
Property, plant and equipment, accumulated depreciation	(28,794)	(27,651)
Total property, plant and equipment, net	71,324	68,595
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	78,596	77,288
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,637	7,524
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,572	8,324
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,313	3,110
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 135,326	$ 131,780