Property, plant and equipment (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 48,977	$ 48,634
Property, plant and equipment, accumulated depreciation	(26,919)	(26,604)
Total property, plant and equipment, net	22,058	22,030
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,157	15,058
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	28,247	28,010
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,573	5,566
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	90,229	89,663
Property, plant and equipment, accumulated depreciation	(19,963)	(19,464)
Total property, plant and equipment, net	70,266	70,199
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	72,194	71,692
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	16,383	16,256
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,652	1,715
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	149,585	148,148
Property, plant and equipment, accumulated depreciation	(41,563)	(40,731)
Total property, plant and equipment, net	108,022	107,417
Utilities and Energy [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,602	4,540
Utilities and Energy [Member] | Machinery, equipment and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,928	3,855
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	96,675	96,195
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	19,357	19,226
Utilities and Energy [Member] | Independent power plants and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,830	14,781
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,193	9,551
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 178,288	$ 177,616