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Goodwill and other intangible assets - Intangible assets - Narrative (Detail) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Finite Lived and Indefinite Lived Intangible Assets [Line Items]      
Amortization expense $ 502 $ 374  
Intangible assets with indefinite lives, excluding goodwill $ 2,274   $ 2,250