Property, plant and equipment (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 48,188	$ 46,298
Property, plant and equipment, accumulated depreciation	(26,430)	(25,185)
Total property, plant and equipment, net	21,758	21,113
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,772	14,761
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	27,973	26,690
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,443	4,847
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	87,775	85,124
Property, plant and equipment, accumulated depreciation	(19,046)	(17,899)
Total property, plant and equipment, net	68,729	67,225
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	69,731	67,350
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	16,125	16,031
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,919	1,743
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	144,642	131,094
Property, plant and equipment, accumulated depreciation	(39,915)	(38,051)
Total property, plant and equipment, net	104,727	93,043
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	93,667	92,759
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	18,800	18,328
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,668	14,650
Utilities and Energy [Member] | Land, buildings, improvements and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,560
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,947	5,357
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 173,456	$ 160,268