Goodwill and other intangible assets - Goodwill (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Balance at beginning of year	$ 62,708	$ 60,714
Acquisitions of businesses	17,016	2,563
Other, including foreign currency translation	(332)	(569)
Balance at end of period	$ 79,392	$ 62,708