Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 13,104	$ 9,026
Accumulated amortization	2,942	2,122
Trademarks and trade names [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	2,655	2,027
Accumulated amortization	219	166
Patents and technology [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	4,900	2,922
Accumulated amortization	1,496	1,013
Customer relationships [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	4,060	2,676
Accumulated amortization	840	612
Other intangible assets [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	1,489	1,401
Accumulated amortization	387	331
Insurance and Other [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	11,016	6,944
Accumulated amortization	2,319	1,816
Railroad, Utilities and Energy [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	2,088	2,082
Accumulated amortization	$ 623	$ 306