Fair value measurements (Details Textual) (USD $)	9 Months Ended		9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 BioVex Group Inc [Member] ContingentConsideration	Sep. 30, 2012 BioVex Group Inc [Member] Other operating expense [Member]	Sep. 30, 2012 BioVex Group Inc [Member] Other operating expense [Member]
Business Combinations [Line Items]
Maximum additional consideration due contingent on certain milestones			$ 575,000,000
Maximum number of contingent consideration payments for achieving regulatory and sales related milestones			8
The number of payments that will potentially be made that each equal the largest potential contingent consideration payment			3
Largest potential contingent consideration payments			125,000,000
Change in fair values of contingent consideration obligations				2,000,000	5,000,000
Fair Value Measurement (Textual) [Abstract]
Length of time hedged in foreign currency contracts	primarily over a three-year time horizon
Aggregate fair value of long-term debt	29,500,000,000	23,000,000,000
Carrying value of long-term debt	$ 26,478,000,000	$ 21,428,000,000