Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 15,504	$ 14,137
Accumulated amortization	5,663	4,954
Trademarks and trade names [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,058	2,750
Accumulated amortization	419	340
Patents and technology [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,412	5,173
Accumulated amortization	3,053	2,626
Customer relationships [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,241	4,690
Accumulated amortization	1,680	1,518
Other intangible assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,793	1,524
Accumulated amortization	511	470
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	13,251	11,923
Accumulated amortization	4,194	3,723
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,253	2,214
Accumulated amortization	$ 1,469	$ 1,231