Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 837	$ 854
Intangible assets with indefinite lives, excluding goodwill	$ 3,140		$ 2,586