Goodwill and other intangible assets - Intangible assets - Narrative (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Finite-lived Intangible Assets [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Amortization expense	$ 809	$ 692	$ 414
Estimated amortization expense - 2012	979
Estimated amortization expense - 2013	959
Estimated amortization expense - 2014	928
Estimated amortization expense - 2015	621
Estimated amortization expense - 2016	570
Unclassified Indefinite-lived Intangible Assets [Member]
Finite Lived and Indefinite Lived Intangible Assets [Line Items]
Intangible assets with indefinite lives, excluding goodwill	$ 2,250	$ 1,635