Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 13,832	$ 13,900
Accumulated amortization	4,133	3,907
Trademarks and trade names [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,799	2,819
Accumulated amortization	293	278
Patents and technology [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,005	5,014
Accumulated amortization	2,179	2,059
Customer relationships [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,532	4,565
Accumulated amortization	1,241	1,155
Other intangible assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,496	1,502
Accumulated amortization	420	415
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	11,669	11,737
Accumulated amortization	3,143	2,994
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,163	2,163
Accumulated amortization	$ 990	$ 913