Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 1,106	$ 1,155	$ 1,090
Estimated amortization expense - 2016	1,009
Estimated amortization expense - 2017	905
Estimated amortization expense - 2018	839
Estimated amortization expense - 2019	733
Estimated amortization expense - 2020	628
Intangible assets with indefinite lives, excluding goodwill	$ 2,964	$ 2,586