Acquisitions and Divestiture (Asset Acquisitions) (Details) - USD ($) $ in Millions	1 Months Ended								3 Months Ended		9 Months Ended
	Sep. 30, 2019	Jul. 31, 2019	Apr. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Jul. 31, 2018	Jun. 30, 2018	Apr. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Acquired IPR&D Expense									$ 77.7	$ 30.0	$ 239.6	$ 1,654.5
AC Immune SA
Business Acquisition [Line Items]
Acquired IPR&D Expense	$ 30.2				$ 96.9						$ 127.1
ImmuNext, Inc.
Business Acquisition [Line Items]
Acquired IPR&D Expense				$ 40.0
Avidity Biosciences, Inc.
Business Acquisition [Line Items]
Acquired IPR&D Expense			$ 25.0
Centrexion Therapeutics Corporation
Business Acquisition [Line Items]
Acquired IPR&D Expense		$ 47.5
Sigilon Therapeutics
Business Acquisition [Line Items]
Acquired IPR&D Expense								$ 66.9
AurKa Pharma, Inc. (Aurka)
Business Acquisition [Line Items]
Acquired IPR&D Expense							$ 81.8
ARMO Biosciences, Inc. (ARMO)
Business Acquisition [Line Items]
Acquired IPR&D Expense							$ 1,475.8
Anima Biotech
Business Acquisition [Line Items]
Acquired IPR&D Expense						$ 30.0