Property, plant and equipment (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 34,965	$ 29,617
Property, plant and equipment, accumulated depreciation	(15,639)	(14,077)
Total property, plant and equipment, net	19,326	15,540
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,315	7,329
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,103	17,054
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,419	3,545
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,128	1,689
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	66,570	64,355
Property, plant and equipment, accumulated depreciation	(5,673)	(4,845)
Total property, plant and equipment, net	60,897	59,510
Railroad [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,060	6,037
Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	47,586	45,967
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,860	11,320
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,064	1,031
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	86,413	84,256
Property, plant and equipment, accumulated depreciation	(24,305)	(23,487)
Total property, plant and equipment, net	62,108	60,769
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	70,316	69,248
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,866	6,755
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,056	5,626
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,175	2,627
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	13,418	12,744
Property, plant and equipment and assets held for lease, accumulated depreciation	(3,681)	(3,397)
Total property, plant and equipment and assets held for lease, net	9,737	9,347
Finance and Financial Products [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	223	220
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	11,906	11,317
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	$ 1,289	$ 1,207
Minimum [Member] | Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Minimum [Member] | Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Minimum [Member] | Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	2 years
Minimum [Member] | Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	7 years
Minimum [Member] | Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	6 years
Minimum [Member] | Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Minimum [Member] | Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Minimum [Member] | Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Minimum [Member] | Finance and Financial Products [Member] | Assets held for lease [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Minimum [Member] | Finance and Financial Products [Member] | Buildings, machinery and other [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Maximum [Member] | Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	40 years
Maximum [Member] | Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Maximum [Member] | Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15 years
Maximum [Member] | Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	100 years
Maximum [Member] | Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	40 years
Maximum [Member] | Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	80 years
Maximum [Member] | Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	80 years
Maximum [Member] | Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	30 years
Maximum [Member] | Finance and Financial Products [Member] | Assets held for lease [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	35 years
Maximum [Member] | Finance and Financial Products [Member] | Buildings, machinery and other [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	50 years