Goodwill and other intangible assets - Intangible assets - Narrative (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Finite-lived Intangible Assets [Member]	Mar. 31, 2013 Finite-lived Intangible Assets [Member]	Mar. 31, 2014 Unclassified Indefinite-lived Intangible Assets [Member]	Dec. 31, 2013 Unclassified Indefinite-lived Intangible Assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Amortization expense	$ 280	$ 264
Intangible assets with indefinite lives, excluding goodwill			$ 2,457	$ 2,221