Property, plant and equipment (Detail) (USD $) In Millions, unless otherwise specified																															6 Months Ended
	Jun. 30, 2013 Insurance and Other [Member]	Dec. 31, 2012 Insurance and Other [Member]	Jun. 30, 2013 Insurance and Other [Member] Buildings and improvements [Member]	Dec. 31, 2012 Insurance and Other [Member] Buildings and improvements [Member]	Jun. 30, 2013 Insurance and Other [Member] Machinery and equipment [Member]	Dec. 31, 2012 Insurance and Other [Member] Machinery and equipment [Member]	Jun. 30, 2013 Insurance and Other [Member] Furniture, fixtures and other [Member]	Dec. 31, 2012 Insurance and Other [Member] Furniture, fixtures and other [Member]	Jun. 30, 2013 Insurance and Other [Member] Assets held for lease [Member]	Dec. 31, 2012 Insurance and Other [Member] Assets held for lease [Member]	Jun. 30, 2013 Insurance and Other [Member] Land [Member]	Dec. 31, 2012 Insurance and Other [Member] Land [Member]	Jun. 30, 2013 Railroad [Member] Land [Member]	Dec. 31, 2012 Railroad [Member] Land [Member]	Jun. 30, 2013 Railroad [Member] Track structure and other roadway [Member]	Dec. 31, 2012 Railroad [Member] Track structure and other roadway [Member]	Jun. 30, 2013 Railroad [Member] Locomotives, freight cars and other equipment [Member]	Dec. 31, 2012 Railroad [Member] Locomotives, freight cars and other equipment [Member]	Jun. 30, 2013 Railroad [Member] Construction in progress [Member]	Dec. 31, 2012 Railroad [Member] Construction in progress [Member]	Jun. 30, 2013 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]	Jun. 30, 2013 Utilities and Energy [Member] Interstate pipeline assets [Member]	Dec. 31, 2012 Utilities and Energy [Member] Interstate pipeline assets [Member]	Jun. 30, 2013 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]	Jun. 30, 2013 Utilities and Energy [Member] Construction in progress [Member]	Dec. 31, 2012 Utilities and Energy [Member] Construction in progress [Member]	Jun. 30, 2013 Railroad, Utilities and Energy [Member]	Dec. 31, 2012 Railroad, Utilities and Energy [Member]	Jun. 30, 2013 Minimum [Member] Insurance and Other [Member] Buildings and improvements [Member]	Jun. 30, 2013 Minimum [Member] Insurance and Other [Member] Machinery and equipment [Member]	Jun. 30, 2013 Minimum [Member] Insurance and Other [Member] Furniture, fixtures and other [Member]	Jun. 30, 2013 Minimum [Member] Insurance and Other [Member] Assets held for lease [Member]	Jun. 30, 2013 Minimum [Member] Railroad [Member] Track structure and other roadway [Member]	Jun. 30, 2013 Minimum [Member] Railroad [Member] Locomotives, freight cars and other equipment [Member]	Jun. 30, 2013 Minimum [Member] Utilities and Energy [Member] Utility generation, distribution and transmission system [Member]	Jun. 30, 2013 Minimum [Member] Utilities and Energy [Member] Interstate pipeline assets [Member]	Jun. 30, 2013 Minimum [Member] Utilities and Energy [Member] Independent power plants and other assets [Member]	Jun. 30, 2013 Maximum [Member] Insurance and Other [Member] Buildings and improvements [Member]	Jun. 30, 2013 Maximum [Member] Insurance and Other [Member] Machinery and equipment [Member]	Jun. 30, 2013 Maximum [Member] Insurance and Other [Member] Furniture, fixtures and other [Member]	Jun. 30, 2013 Maximum [Member] Insurance and Other [Member] Assets held for lease [Member]	Jun. 30, 2013 Maximum [Member] Railroad [Member] Track structure and other roadway [Member]	Jun. 30, 2013 Maximum [Member] Railroad [Member] Locomotives, freight cars and other equipment [Member]	Jun. 30, 2013 Maximum [Member] Utilities and Energy [Member] Utility generation, distribution and transmission system [Member]	Jun. 30, 2013 Maximum [Member] Utilities and Energy [Member] Interstate pipeline assets [Member]	Jun. 30, 2013 Maximum [Member] Utilities and Energy [Member] Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 32,685	$ 32,025	$ 6,052	$ 6,074	$ 15,677	$ 15,436	$ 2,945	$ 2,736	$ 6,956	$ 6,731	$ 1,055	$ 1,048	$ 5,970	$ 5,950	$ 38,798	$ 38,255	$ 6,804	$ 6,528	$ 1,160	$ 963	$ 43,162	$ 42,682	$ 6,357	$ 6,354	$ 2,311	$ 1,860	$ 2,819	$ 2,647	$ 107,381	$ 105,239
Accumulated depreciation	(13,535)	(12,837)																											(18,182)	(17,555)
Total Property, plant and equipment, net	$ 19,150	$ 19,188																											$ 89,199	$ 87,684
Estimated useful life (in years)																															2 years	3 years	2 years	12 years	5 years	5 years	5 years	3 years	3 years	40 years	20 years	20 years	30 years	100 years	37 years	80 years	80 years	30 years