Property, plant and equipment and assets held for lease (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	$ 13,993	$ 13,428
Property, plant and equipment and assets held for lease, accumulated depreciation	(4,062)	(3,739)
Total property, plant and equipment and assets held for lease, net	9,931	9,689
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	12,318	11,902
Finance and Financial Products [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	231	224
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	1,444	1,302
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	37,424	35,011
Property, plant and equipment, accumulated depreciation	(17,320)	(15,686)
Total property, plant and equipment, net	20,104	19,325
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,292	2,108
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,810	8,360
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	21,935	20,463
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,387	4,080
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	70,940	67,380
Property, plant and equipment, accumulated depreciation	(8,627)	(6,130)
Total property, plant and equipment, net	62,313	61,250
Railroad [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,088	6,063
Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	51,320	48,277
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	12,543	12,075
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	989	965
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	91,891	87,172
Property, plant and equipment, accumulated depreciation	(26,020)	(24,663)
Total property, plant and equipment, net	65,871	62,509
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	74,660	71,536
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,176	6,942
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,499	6,596
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,556	2,098
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 128,184	$ 123,759