Property, plant and equipment (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 44,987	$ 44,773
Property, plant and equipment, accumulated depreciation	(24,280)	(23,939)
Total property, plant and equipment, net	20,707	20,834
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,049	14,070
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	26,166	26,063
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,772	4,640
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	82,267	80,692
Property, plant and equipment, accumulated depreciation	(16,535)	(14,978)
Total property, plant and equipment, net	65,732	65,714
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	65,256	65,843
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,910	13,822
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,101	1,027
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	126,677	125,537
Property, plant and equipment, accumulated depreciation	(36,394)	(35,721)
Total property, plant and equipment, net	90,283	89,816
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	90,560	90,223
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17,526	17,423
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,986	13,695
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,605	4,196
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 156,015	$ 155,530