Property, plant and equipment (Detail) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 71,844	$ 62,979
Property, plant and equipment, accumulated depreciation	(32,435)	(31,094)
Total property, plant and equipment, net	39,409	31,885
Insurance and Other [Member] \| Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	23,775	22,034
Insurance and Other [Member] \| Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	39,639	34,733
Insurance and Other [Member] \| Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,430	6,212
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	95,991	94,699
Property, plant and equipment, accumulated depreciation	(23,215)	(22,327)
Total property, plant and equipment, net	72,776	72,372
Railroad [Member] \| Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	77,573	76,764
Railroad [Member] \| Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,982	15,772
Railroad [Member] \| Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,436	2,163
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	158,598	157,370
Property, plant and equipment, accumulated depreciation	(45,559)	(45,002)
Total property, plant and equipment, net	113,039	112,368
Utilities and Energy [Member] \| Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	109,292	109,815
Utilities and Energy [Member] \| Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	21,683	21,334
Utilities and Energy [Member] \| Independent power plants and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,699	15,630
Utilities and Energy [Member] \| Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,924	10,591
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 185,815	$ 184,740