Property, plant and equipment (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 59,516	$ 58,711
Property, plant and equipment, accumulated depreciation	(29,301)	(28,640)
Total property, plant and equipment, net	30,215	30,071
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,951	20,735
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	32,866	32,475
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,699	5,501
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	92,214	91,672
Property, plant and equipment, accumulated depreciation	(20,969)	(20,411)
Total property, plant and equipment, net	71,245	71,261
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	74,882	74,093
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,463	15,766
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,869	1,813
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	149,321	146,885
Property, plant and equipment, accumulated depreciation	(44,007)	(43,116)
Total property, plant and equipment, net	105,314	103,769
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	104,030	103,015
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,327	20,237
Utilities and Energy [Member] | Independent power plants and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,389	14,840
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,575	8,793
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 176,559	$ 175,030