Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 14,211	$ 13,900
Accumulated amortization	4,672	3,907
Trademarks and trade names [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,865	2,819
Accumulated amortization	326	278
Patents and technology [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,162	5,014
Accumulated amortization	2,470	2,059
Customer relationships [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,660	4,565
Accumulated amortization	1,421	1,155
Other Intangible Assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,524	1,502
Accumulated amortization	455	415
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	12,013	11,737
Accumulated amortization	3,525	2,994
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,198	2,163
Accumulated amortization	$ 1,147	$ 913