Acquisitions and Divestiture (Asset Acquisitions) (Details) - USD ($) $ in Millions	1 Months Ended					3 Months Ended		6 Months Ended
	Apr. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Jun. 30, 2018	Apr. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition [Line Items]
Acquired in-process research and development						$ 25.0	$ 1,624.5	$ 161.9	$ 1,624.5
AC Immune SA
Business Acquisition [Line Items]
Acquired in-process research and development			$ 96.9
ImmuNext, Inc.
Business Acquisition [Line Items]
Acquired in-process research and development		$ 40.0
Avidity Biosciences, Inc.
Business Acquisition [Line Items]
Acquired in-process research and development	$ 25.0
Sigilon Therapeutics
Business Acquisition [Line Items]
Acquired in-process research and development					$ 66.9
AurKa Pharma, Inc.
Business Acquisition [Line Items]
Acquired in-process research and development				$ 81.8
ARMO Biosciences, Inc.
Business Acquisition [Line Items]
Acquired in-process research and development				$ 1,475.8