Collaborative and Other Relationships (Details 5) (Portola Pharmaceuticals, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Portola Pharmaceuticals
Summary of activity related to collaboration with Portola Pharmaceuticals, Inc.
Total expense incurred by collaboration	$ 18.8	$ 1.1	$ 0
Total expense reflected within our consolidated statements of income, excluding upfront and milestone payments	14.2	0.9	0
Summary of activity related to collaboration, along with an estimate of additional future development expense
Total upfront and milestone payments made to Collaborative Partner	36.8
Total expense incurred by Biogen Idec, excluding upfront and milestone payments	15.1
Estimate of additional amounts to be incurred by us in development of the lead compound	$ 695.1