Property, plant and equipment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 33,457	$ 29,617
Property, plant and equipment, accumulated depreciation	(14,499)	(14,077)
Total property, plant and equipment, net	18,958	15,540
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,987	7,329
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	19,204	17,054
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,213	3,545
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,053	1,689
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	65,035	64,355
Property, plant and equipment, accumulated depreciation	(5,135)	(4,845)
Total property, plant and equipment, net	59,900	59,510
Railroad [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,054	6,037
Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	46,435	45,967
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,515	11,320
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,031	1,031
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	85,100	84,256
Property, plant and equipment, accumulated depreciation	(23,948)	(23,487)
Total property, plant and equipment, net	61,152	60,769
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	69,880	69,248
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,798	6,755
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,665	5,626
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,757	2,627
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	13,035	12,744
Property, plant and equipment and assets held for lease, accumulated depreciation	(3,510)	(3,397)
Total property, plant and equipment and assets held for lease, net	9,525	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	221	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	11,576	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	$ 1,238	$ 1,207
Minimum [Member] | Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	2 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)	18 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