Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 13,879	$ 13,900
Accumulated amortization	4,400	3,907
Trademarks and trade names [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,801	2,819
Accumulated amortization	310	278
Patents and technology [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,035	5,014
Accumulated amortization	2,329	2,059
Customer relationships [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,538	4,565
Accumulated amortization	1,325	1,155
Other Intangible Assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,505	1,502
Accumulated amortization	436	415
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	11,715	11,737
Accumulated amortization	3,330	2,994
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,164	2,163
Accumulated amortization	$ 1,070	$ 913