Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 15,138	$ 14,137
Accumulated amortization	5,245	4,954
Trademarks and trade names [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,988	2,750
Accumulated amortization	365	340
Patents and technology [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,667	5,173
Accumulated amortization	2,771	2,626
Customer relationships [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,880	4,690
Accumulated amortization	1,618	1,518
Other intangible assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,603	1,524
Accumulated amortization	491	470
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	12,924	11,923
Accumulated amortization	3,936	3,723
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,214	2,214
Accumulated amortization	$ 1,309	$ 1,231