Property, plant and equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 48,634	$ 46,298
Property, plant and equipment, accumulated depreciation	(26,604)	(25,185)
Total property, plant and equipment, net	22,030	21,113
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	28,010	26,690
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,566	4,847
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,058	14,761
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	89,663	85,124
Property, plant and equipment, accumulated depreciation	(19,464)	(17,899)
Total property, plant and equipment, net	70,199	67,225
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	71,692	67,350
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	16,256	16,031
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,715	1,743
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	148,148	131,094
Property, plant and equipment, accumulated depreciation	(40,731)	(38,051)
Total property, plant and equipment, net	107,417	93,043
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	96,195	92,759
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	19,226	18,328
Utilities and Energy [Member] | Independent power plants and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,781	14,650
Utilities and Energy [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,540
Utilities and Energy [Member] | Machinery, equipment, and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,855
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,551	5,357
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 177,616	$ 160,268