Property, plant and equipment (Detail) (USD $) In Millions, unless otherwise specified																															9 Months Ended
	Sep. 30, 2013 Insurance and Other [Member]	Dec. 31, 2012 Insurance and Other [Member]	Sep. 30, 2013 Insurance and Other [Member] Buildings and improvements [Member]	Dec. 31, 2012 Insurance and Other [Member] Buildings and improvements [Member]	Sep. 30, 2013 Insurance and Other [Member] Machinery and equipment [Member]	Dec. 31, 2012 Insurance and Other [Member] Machinery and equipment [Member]	Sep. 30, 2013 Insurance and Other [Member] Furniture, fixtures and other [Member]	Dec. 31, 2012 Insurance and Other [Member] Furniture, fixtures and other [Member]	Sep. 30, 2013 Insurance and Other [Member] Assets held for lease [Member]	Dec. 31, 2012 Insurance and Other [Member] Assets held for lease [Member]	Sep. 30, 2013 Insurance and Other [Member] Land [Member]	Dec. 31, 2012 Insurance and Other [Member] Land [Member]	Sep. 30, 2013 Railroad [Member] Land [Member]	Dec. 31, 2012 Railroad [Member] Land [Member]	Sep. 30, 2013 Railroad [Member] Track structure and other roadway [Member]	Dec. 31, 2012 Railroad [Member] Track structure and other roadway [Member]	Sep. 30, 2013 Railroad [Member] Locomotives, freight cars and other equipment [Member]	Dec. 31, 2012 Railroad [Member] Locomotives, freight cars and other equipment [Member]	Sep. 30, 2013 Railroad [Member] Construction in progress [Member]	Dec. 31, 2012 Railroad [Member] Construction in progress [Member]	Sep. 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]	Sep. 30, 2013 Utilities and Energy [Member] Interstate pipeline assets [Member]	Dec. 31, 2012 Utilities and Energy [Member] Interstate pipeline assets [Member]	Sep. 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]	Sep. 30, 2013 Utilities and Energy [Member] Construction in progress [Member]	Dec. 31, 2012 Utilities and Energy [Member] Construction in progress [Member]	Sep. 30, 2013 Railroad, Utilities and Energy [Member]	Dec. 31, 2012 Railroad, Utilities and Energy [Member]	Sep. 30, 2013 Minimum [Member] Insurance and Other [Member] Buildings and improvements [Member]	Sep. 30, 2013 Minimum [Member] Insurance and Other [Member] Machinery and equipment [Member]	Sep. 30, 2013 Minimum [Member] Insurance and Other [Member] Furniture, fixtures and other [Member]	Sep. 30, 2013 Minimum [Member] Insurance and Other [Member] Assets held for lease [Member]	Sep. 30, 2013 Minimum [Member] Railroad [Member] Track structure and other roadway [Member]	Sep. 30, 2013 Minimum [Member] Railroad [Member] Locomotives, freight cars and other equipment [Member]	Sep. 30, 2013 Minimum [Member] Utilities and Energy [Member] Utility generation, distribution and transmission system [Member]	Sep. 30, 2013 Minimum [Member] Utilities and Energy [Member] Interstate pipeline assets [Member]	Sep. 30, 2013 Minimum [Member] Utilities and Energy [Member] Independent power plants and other assets [Member]	Sep. 30, 2013 Maximum [Member] Insurance and Other [Member] Buildings and improvements [Member]	Sep. 30, 2013 Maximum [Member] Insurance and Other [Member] Machinery and equipment [Member]	Sep. 30, 2013 Maximum [Member] Insurance and Other [Member] Furniture, fixtures and other [Member]	Sep. 30, 2013 Maximum [Member] Insurance and Other [Member] Assets held for lease [Member]	Sep. 30, 2013 Maximum [Member] Railroad [Member] Track structure and other roadway [Member]	Sep. 30, 2013 Maximum [Member] Railroad [Member] Locomotives, freight cars and other equipment [Member]	Sep. 30, 2013 Maximum [Member] Utilities and Energy [Member] Utility generation, distribution and transmission system [Member]	Sep. 30, 2013 Maximum [Member] Utilities and Energy [Member] Interstate pipeline assets [Member]	Sep. 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	$ 33,418	$ 32,025	$ 6,261	$ 6,074	$ 16,008	$ 15,436	$ 2,934	$ 2,736	$ 7,111	$ 6,731	$ 1,104	$ 1,048	$ 5,968	$ 5,950	$ 39,420	$ 38,255	$ 7,082	$ 6,528	$ 1,112	$ 963	$ 43,899	$ 42,682	$ 6,388	$ 6,354	$ 2,424	$ 1,860	$ 3,504	$ 2,647	$ 109,797	$ 105,239
Accumulated depreciation	(13,957)	(12,837)																											(18,702)	(17,555)
Total property, plant and equipment, net	$ 19,461	$ 19,188																											$ 91,095	$ 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