Property, plant and equipment (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 42,158	$ 42,210
Property, plant and equipment, accumulated depreciation	(20,900)	(20,772)
Total property, plant and equipment, net	21,258	21,438
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,277	13,259
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	24,231	24,285
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,650	4,666
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	76,798	76,634
Property, plant and equipment, accumulated depreciation	(12,198)	(12,101)
Total property, plant and equipment, net	64,600	64,533
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	62,643	62,404
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,382	13,482
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	773	748
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	101,322	101,841
Property, plant and equipment, accumulated depreciation	(28,658)	(28,536)
Total property, plant and equipment, net	72,664	73,305
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	80,530	81,127
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,181	8,165
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,792	8,817
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,819	3,732
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 137,264	$ 137,838