Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Amortization expense	$ 339	$ 255
Indefinite-lived Intangible Assets Excluding Business Acquisitions Completed in 2016 [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible assets with indefinite lives, excluding goodwill	3,000		$ 3,000
Precision Castparts and Duracell [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Other intangible assets	26,000
Intangible assets with indefinite lives, excluding goodwill	$ 17,000