Collaborative Arrangements and Licensing Agreements, Strategic Partnership - Biogen (Neurology) (Details) - Biogen [Member] - Agreement Entered into in December 2012 [Member] - Neurology [Member] $ in Millions	1 Months Ended
	Feb. 29, 2016 USD ($)	Dec. 31, 2012 USD ($) Target Program	Mar. 31, 2016 USD ($)
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of targets | Target		3
Number of programs under which drugs are to be developed and commercialized | Program		3
Upfront payment recorded as deferred revenue		$ 30
Cumulative payments received			$ 43
Milestone payment earned	$ 3
Next prospective milestone			10
License Fee and Substantive Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per program			259
Development Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per program			59
Regulatory Milestones [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payment receivable per program			$ 130