Property, plant and equipment and assets held for lease (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	$ 14,230	$ 13,993
Property, plant and equipment and assets held for lease, accumulated depreciation	(4,165)	(4,062)
Total property, plant and equipment and assets held for lease, net	10,065	9,931
Finance and Financial Products [Member] | Assets held for lease [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	12,507	12,318
Finance and Financial Products [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	234	231
Finance and Financial Products [Member] | Buildings, machinery and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	1,489	1,444
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	43,957	37,424
Property, plant and equipment, accumulated depreciation	(20,009)	(17,320)
Total property, plant and equipment, net	23,948	20,104
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,289	2,292
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,041	8,810
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	27,932	21,935
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,695	4,387
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	71,766	70,940
Property, plant and equipment, accumulated depreciation	(9,259)	(8,627)
Total property, plant and equipment, net	62,507	62,313
Railroad [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,093	6,088
Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	51,994	51,320
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	12,640	12,543
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,039	989
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	93,561	91,891
Property, plant and equipment, accumulated depreciation	(26,852)	(26,020)
Total property, plant and equipment, net	66,709	65,871
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	74,975	74,660
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,240	7,176
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,142	7,499
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,204	2,556
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 129,216	$ 128,184