Property, plant and equipment (Detail) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 45,009	$ 44,773
Property, plant and equipment, accumulated depreciation	(24,492)	(23,939)
Total property, plant and equipment, net	20,517	20,834
Insurance and Other [Member] | Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,055	14,070
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	26,082	26,063
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,872	4,640
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	82,964	80,692
Property, plant and equipment, accumulated depreciation	(16,988)	(14,978)
Total property, plant and equipment, net	65,976	65,714
Railroad [Member] | Land, track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	65,821	65,843
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,957	13,822
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,186	1,027
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	127,619	125,537
Property, plant and equipment, accumulated depreciation	(36,824)	(35,721)
Total property, plant and equipment, net	90,795	89,816
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	90,810	90,223
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17,547	17,423
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,488	13,695
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,774	4,196
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 156,771	$ 155,530