Property, plant and equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 58,711	$ 57,313
Property, plant and equipment, accumulated depreciation	(28,640)	(27,114)
Total property, plant and equipment, net	30,071	30,199
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,735	19,598
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	32,475	31,865
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,501	5,850
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	91,672	89,663
Property, plant and equipment, accumulated depreciation	(20,411)	(19,464)
Total property, plant and equipment, net	71,261	70,199
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	74,093	71,692
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,766	16,256
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,813	1,715
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	146,885	139,469
Property, plant and equipment, accumulated depreciation	(43,116)	(40,221)
Total property, plant and equipment, net	103,769	99,248
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	103,015	96,195
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,237	19,226
Utilities and Energy [Member] | Independent power plants and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,840	14,781
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,793	9,267
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 175,030	$ 169,447