Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 12,788	$ 9,026
Accumulated amortization	2,675	2,122
Insurance and Other [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	10,699	6,944
Accumulated amortization	2,126	1,816
Railroad, Utilities and Energy [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	2,089	2,082
Accumulated amortization	549	306
Trademarks and trade names [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	2,566	2,027
Accumulated amortization	205	166
Patents and technology [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	4,971	2,922
Accumulated amortization	1,323	1,013
Customer relationships [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	3,831	2,676
Accumulated amortization	753	612
Other intangible assets [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Gross carrying amount	1,420	1,401
Accumulated amortization	$ 394	$ 331