Goodwill and other intangible assets - Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Balance at beginning of year	$ 62,708	$ 60,714
Acquisitions of businesses	17,650	2,563
Other, including foreign currency translation	(872)	(569)
Balance at end of year	$ 79,486	$ 62,708