Property, plant and equipment (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 25,208	$ 24,742
Accumulated depreciation	(9,563)	(9,001)
Total Property, plant and equipment, net	15,645	15,741
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	760	744
Insurance and Other [Member] | Building and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,842	4,661
Estimated useful life, minimum (In years)	3
Estimated useful life, maximum (In years)	40
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,707	11,573
Estimated useful life, minimum (In years)	3
Estimated useful life, maximum (In years)	25
Insurance and Other [Member] | Furniture fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,061	1,932
Estimated useful life, minimum (In years)	3
Estimated useful life, maximum (In years)	20
Insurance and Other [Member] | Assets held for lease [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,838	5,832
Estimated useful life, minimum (In years)	12
Estimated useful life, maximum (In years)	30
Railroad [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,913	5,901
Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	35,952	35,463
Estimated useful life, minimum (In years)	5
Estimated useful life, maximum (In years)	100
Railroad [Member] | Locomotives freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,757	4,329
Estimated useful life, minimum (In years)	5
Estimated useful life, maximum (In years)	37
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	747	453
Utilities and Energy [Member] | Utility generation, distribution and transmission system [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	38,542	37,643
Estimated useful life, minimum (In years)	5
Estimated useful life, maximum (In years)	85
Utilities and Energy [Member] | Interstate pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,940	5,906
Estimated useful life, minimum (In years)	3
Estimated useful life, maximum (In years)	67
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,100	1,097
Estimated useful life, minimum (In years)	3
Estimated useful life, maximum (In years)	30
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,769	1,456
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	94,720	92,248
Accumulated depreciation	(15,413)	(14,863)
Total Property, plant and equipment, net	$ 79,307	$ 77,385