Acquisitions and Divestiture (Asset Acquisitions) (Details) - USD ($) $ in Millions	1 Months Ended															3 Months Ended								9 Months Ended	12 Months Ended
	Sep. 30, 2019	Jul. 31, 2019	Apr. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Dec. 31, 2018	Nov. 30, 2018	Oct. 31, 2018	Jul. 31, 2018	Jun. 30, 2018	Apr. 30, 2018	Nov. 30, 2017	Aug. 31, 2017	Jul. 31, 2017	Mar. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Acquired IPR&D																$ 0.0	$ 77.7	$ 25.0	$ 136.9	$ 329.4	$ 30.0	$ 1,624.5	$ 0.0		$ 239.6	$ 1,983.9	$ 1,112.6
AC Immune SA
Business Acquisition [Line Items]
Acquired IPR&D	$ 30.2				$ 96.9																			$ 127.1
ImmuNext, Inc.
Business Acquisition [Line Items]
Acquired IPR&D				$ 40.0
Avidity Biosciences, Inc.
Business Acquisition [Line Items]
Acquired IPR&D			$ 25.0
Centrexion Therapeutics Corporation
Business Acquisition [Line Items]
Acquired IPR&D		$ 47.5
Sigilon Therapeutics
Business Acquisition [Line Items]
Acquired IPR&D											$ 66.9
AurKa Pharma, Inc.
Business Acquisition [Line Items]
Acquired IPR&D										$ 81.8
ARMO BioSciences, Inc. (ARMO)
Business Acquisition [Line Items]
Acquired IPR&D										$ 1,475.8
Anima Biotech
Business Acquisition [Line Items]
Acquired IPR&D									$ 30.0
SIGA Technologies, Inc.
Business Acquisition [Line Items]
Acquired IPR&D								$ 80.0
Chugai Pharmaceutical Company
Business Acquisition [Line Items]
Acquired IPR&D								$ 50.0
NextCure, Inc.
Business Acquisition [Line Items]
Acquired IPR&D							$ 28.1
Dicerna Pharmaceuticals, Inc.
Business Acquisition [Line Items]
Acquired IPR&D						$ 148.7
Hydra Biosciences
Business Acquisition [Line Items]
Acquired IPR&D						$ 22.6
CoLucid Pharmaceuticals, Inc. (CoLucid)
Business Acquisition [Line Items]
Acquired IPR&D															$ 857.6
KeyBioscience AG
Business Acquisition [Line Items]
Acquired IPR&D														$ 55.0
Nektar Therapeutics
Business Acquisition [Line Items]
Acquired IPR&D													$ 150.0
CureVac AG
Business Acquisition [Line Items]
Acquired IPR&D												$ 50.0