Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 15,570	$ 15,968
Accumulated amortization	5,124	6,027
Trademarks and trade names [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,057	3,117
Accumulated amortization	651	599
Patents and technology [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,196	5,425
Accumulated amortization	1,916	3,133
Customer relationships [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,439	5,603
Accumulated amortization	1,947	1,768
Other intangible assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,878	1,823
Accumulated amortization	610	527
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	14,700	13,714
Accumulated amortization	4,911	4,476
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	870	2,254
Accumulated amortization	$ 213	$ 1,551