Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Amortization expense	$ 1,085	$ 837
Precision Castparts and Duracell [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Other intangible assets	26,200
Intangible assets with indefinite lives, excluding goodwill	17,600
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