Property, plant and equipment (Detail) (USD $) In Millions, unless otherwise specified							12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended						12 Months Ended				12 Months Ended								12 Months Ended				12 Months Ended				12 Months Ended
	Dec. 31, 2012 Insurance and Other [Member]	Dec. 31, 2011 Insurance and Other [Member]	Dec. 31, 2012 Insurance and Other [Member] Land [Member]	Dec. 31, 2011 Insurance and Other [Member] Land [Member]	Dec. 31, 2012 Insurance and Other [Member] Buildings and improvements [Member]	Dec. 31, 2011 Insurance and Other [Member] Buildings and improvements [Member]	Dec. 31, 2012 Insurance and Other [Member] Buildings and improvements [Member] Minimum [Member]	Dec. 31, 2012 Insurance and Other [Member] Buildings and improvements [Member] Maximum [Member]	Dec. 31, 2012 Insurance and Other [Member] Machinery and equipment [Member]	Dec. 31, 2011 Insurance and Other [Member] Machinery and equipment [Member]	Dec. 31, 2012 Insurance and Other [Member] Machinery and equipment [Member] Minimum [Member]	Dec. 31, 2012 Insurance and Other [Member] Machinery and equipment [Member] Maximum [Member]	Dec. 31, 2012 Insurance and Other [Member] Furniture, fixtures and other [Member]	Dec. 31, 2011 Insurance and Other [Member] Furniture, fixtures and other [Member]	Dec. 31, 2012 Insurance and Other [Member] Furniture, fixtures and other [Member] Minimum [Member]	Dec. 31, 2012 Insurance and Other [Member] Furniture, fixtures and other [Member] Maximum [Member]	Dec. 31, 2012 Insurance and Other [Member] Assets held for lease [Member]	Dec. 31, 2011 Insurance and Other [Member] Assets held for lease [Member]	Dec. 31, 2012 Insurance and Other [Member] Assets held for lease [Member] Minimum [Member]	Dec. 31, 2012 Insurance and Other [Member] Assets held for lease [Member] Maximum [Member]	Dec. 31, 2012 Railroad [Member] Land [Member]	Dec. 31, 2011 Railroad [Member] Land [Member]	Dec. 31, 2012 Railroad [Member] Track structure and other roadway [Member]	Dec. 31, 2011 Railroad [Member] Track structure and other roadway [Member]	Dec. 31, 2012 Railroad [Member] Track structure and other roadway [Member] Minimum [Member]	Dec. 31, 2012 Railroad [Member] Track structure and other roadway [Member] Maximum [Member]	Dec. 31, 2012 Railroad [Member] Locomotives, freight cars and other equipment [Member]	Dec. 31, 2011 Railroad [Member] Locomotives, freight cars and other equipment [Member]	Dec. 31, 2012 Railroad [Member] Locomotives, freight cars and other equipment [Member] Minimum [Member]	Dec. 31, 2012 Railroad [Member] Locomotives, freight cars and other equipment [Member] Maximum [Member]	Dec. 31, 2012 Railroad [Member] Construction in progress [Member]	Dec. 31, 2011 Railroad [Member] Construction in progress [Member]	Dec. 31, 2012 Utilities and Energy [Member] Construction in progress [Member]	Dec. 31, 2011 Utilities and Energy [Member] Construction in progress [Member]	Dec. 31, 2012 Utilities and Energy [Member] Utility generation, distribution and transmission system [Member]	Dec. 31, 2011 Utilities and Energy [Member] Utility generation, distribution and transmission system [Member]	Dec. 31, 2012 Utilities and Energy [Member] Utility generation, distribution and transmission system [Member] Minimum [Member]	Dec. 31, 2012 Utilities and Energy [Member] Utility generation, distribution and transmission system [Member] Maximum [Member]	Dec. 31, 2012 Utilities and Energy [Member] Interstate pipeline assets [Member]	Dec. 31, 2011 Utilities and Energy [Member] Interstate pipeline assets [Member]	Dec. 31, 2012 Utilities and Energy [Member] Interstate pipeline assets [Member] Minimum [Member]	Dec. 31, 2012 Utilities and Energy [Member] Interstate pipeline assets [Member] Maximum [Member]	Dec. 31, 2012 Utilities and Energy [Member] Independent power plants and other assets [Member]	Dec. 31, 2011 Utilities and Energy [Member] Independent power plants and other assets [Member]	Dec. 31, 2012 Utilities and Energy [Member] Independent power plants and other assets [Member] Minimum [Member]	Dec. 31, 2012 Utilities and Energy [Member] Independent power plants and other assets [Member] Maximum [Member]	Dec. 31, 2012 Railroad, Utilities and Energy [Member]	Dec. 31, 2011 Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)							2 years	40 years			3 years	20 years			2 years	20 years			12 years	30 years					5 years	100 years			5 years	37 years							5 years	80 years			3 years	80 years			3 years	30 years
Property, plant and equipment, gross	$ 32,025	$ 28,352	$ 1,048	$ 940	$ 6,074	$ 5,429			$ 15,436	$ 13,589			$ 2,736	$ 2,397			$ 6,731	$ 5,997			$ 5,950	$ 5,925	$ 38,255	$ 36,760			$ 6,528	$ 5,533			$ 963	$ 885	$ 2,647	$ 1,559	$ 42,682	$ 40,180			$ 6,354	$ 6,245			$ 1,860	$ 1,106			$ 105,239	$ 98,193
Accumulated depreciation	(12,837)	(10,175)																																													(17,555)	(15,979)
Total Property, plant and equipment, net	$ 19,188	$ 18,177																																													$ 87,684	$ 82,214