Property, plant and equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 39,827	$ 37,641
Property, plant and equipment, accumulated depreciation	(19,199)	(17,773)
Total property, plant and equipment, net	20,628	19,868
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,536	2,523
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,959	9,409
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	22,574	21,190
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,758	4,519
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	73,189	70,940
Property, plant and equipment, accumulated depreciation	(10,004)	(8,627)
Total property, plant and equipment, net	63,185	62,313
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	59,509	57,408
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,016	12,543
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	664	989
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	96,246	91,891
Property, plant and equipment, accumulated depreciation	(27,651)	(26,020)
Total property, plant and equipment, net	68,595	65,871
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	77,288	74,660
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,524	7,176
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,324	7,499
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,110	2,556
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 131,780	$ 128,184