Property, plant and equipment - Narrative (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 19,732	$ 19,188
Insurance and Other [Member] | Equipment lease fleet [Member]
Property, Plant and Equipment [Line Items]
Future minimum lease rentals to be received, 2014	855
Future minimum lease rentals to be received, 2015	709
Future minimum lease rentals to be received, 2016	559
Future minimum lease rentals to be received, 2017	405
Future minimum lease rentals to be received, 2018	253
Future minimum lease rentals to be received, thereafter	333
Utilities and Energy [Member] | NV Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 9,600