Goodwill and other intangible assets - Intangible assets - Narrative (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Finite-lived Intangible Assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Amortization expense	$ 1,008	$ 809	$ 692
Estimated amortization expense - 2013	1,190
Estimated amortization expense - 2014	1,076
Estimated amortization expense - 2015	733
Estimated amortization expense - 2016	639
Estimated amortization expense - 2017	539
Unclassified Indefinite-lived Intangible Assets [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible assets with indefinite lives, excluding goodwill	$ 2,328	$ 2,250