Goodwill and other intangible assets - Intangible assets (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 15,136	$ 14,137
Accumulated amortization	5,404	4,954
Trademarks and trade names [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,011	2,750
Accumulated amortization	392	340
Patents and technology [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,703	5,173
Accumulated amortization	2,920	2,626
Customer relationships [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,786	4,690
Accumulated amortization	1,587	1,518
Other intangible assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,636	1,524
Accumulated amortization	505	470
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	12,882	11,923
Accumulated amortization	4,017	3,723
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,254	2,214
Accumulated amortization	$ 1,387	$ 1,231