Goodwill and other intangible assets (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Goodwill [Line Items]
Balance at beginning of year	$ 54,523	$ 53,213
Acquisitions of businesses	15	1,442
Other, including foreign currency translation	(166)	(132)
Balance at end of period	$ 54,372	$ 54,523