Property, plant and equipment (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Year	Dec. 31, 2010
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 28,352	$ 24,742
Accumulated depreciation	(10,175)	(9,001)
Total Property, plant and equipment, net	18,177	15,741
Insurance and Other [Member] | Building and building improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	3
Estimated useful life, maximum (in years)	40
Property, plant and equipment, gross	5,429	4,661
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	3
Estimated useful life, maximum (in years)	25
Property, plant and equipment, gross	13,589	11,573
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	2
Estimated useful life, maximum (in years)	20
Property, plant and equipment, gross	2,397	1,932
Insurance and Other [Member] | Assets held for lease [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	12
Estimated useful life, maximum (in years)	30
Property, plant and equipment, gross	5,997	5,832
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	940	744
Railroad [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,925	5,901
Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	5
Estimated useful life, maximum (in years)	100
Property, plant and equipment, gross	36,760	35,463
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	5
Estimated useful life, maximum (in years)	37
Property, plant and equipment, gross	5,533	4,329
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	885	453
Utilities and Energy [Member] | Utility generation, distribution and transmission system [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	5
Estimated useful life, maximum (in years)	80
Property, plant and equipment, gross	40,180	37,643
Utilities and Energy [Member] | Interstate pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	3
Estimated useful life, maximum (in years)	80
Property, plant and equipment, gross	6,245	5,906
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (in years)	3
Estimated useful life, maximum (in years)	30
Property, plant and equipment, gross	1,106	1,097
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,559	1,456
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	98,193	92,248
Accumulated depreciation	(15,979)	(14,863)
Total Property, plant and equipment, net	$ 82,214	$ 77,385