Acquisitions and Divestiture (Asset Acquisitions) (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2019	Jan. 31, 2019	Mar. 31, 2019	Mar. 31, 2018
Business Acquisition [Line Items]
Acquired in-process research and development (Note 3)			$ 136.9	$ 0.0
AC Immune SA
Business Acquisition [Line Items]
Acquired in-process research and development (Note 3)		$ 96.9
ImmuNext, Inc.
Business Acquisition [Line Items]
Acquired in-process research and development (Note 3)	$ 40.0