Acquisitions and Divestiture (Asset Acquisitions) (Details) - USD ($) $ in Millions	1 Months Ended																12 Months Ended
	Nov. 30, 2020	Oct. 31, 2020	Jun. 30, 2020	May 31, 2020	Mar. 31, 2020	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	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Acquired IPR&D charges																	$ 660.4	$ 239.6	$ 1,980.0
Sitryx Therapeutics Limited
Business Acquisition [Line Items]
Acquired IPR&D charges					$ 52.3
AbCellera Biologics Inc. (AbCellera)
Business Acquisition [Line Items]
Acquired IPR&D charges				$ 25.0	$ 25.0												25.0
Shanghai Junshi Biosciences Co., Ltd. (Junshi Biosciences)
Business Acquisition [Line Items]
Acquired IPR&D charges				20.0													20.0
Undisclosed
Business Acquisition [Line Items]
Acquired IPR&D charges				$ 174.8
Evox Therapeutics Ltd
Business Acquisition [Line Items]
Acquired IPR&D charges			$ 22.0
Innovent Biologics, Inc. (Innovent)
Business Acquisition [Line Items]
Acquired IPR&D charges		$ 200.0															$ 200.0
Disarm Therapeutics, Inc. (Disarm)
Business Acquisition [Line Items]
Acquired IPR&D charges		$ 126.3
Fochon Pharmaceuticals, Ltd.
Business Acquisition [Line Items]
Acquired IPR&D charges	$ 40.0
AC Immune SA
Business Acquisition [Line Items]
Acquired IPR&D charges						$ 30.2				$ 96.9								$ 127.1
ImmuNext, Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges									$ 40.0
Avidity Biosciences, Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges								$ 25.0
Centrexion Therapeutics Corporation
Business Acquisition [Line Items]
Acquired IPR&D charges							$ 47.5
Sigilon Therapeutics, Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges																$ 66.9
AurKa Pharma Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges															$ 81.8
ARMO BioSciences, Inc. (ARMO)
Business Acquisition [Line Items]
Acquired IPR&D charges															$ 1,475.8
Anima Biotech Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges														$ 30.0
SIGA Technologies, Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges													$ 80.0
Chugai Pharmaceutical Co., Ltd.
Business Acquisition [Line Items]
Acquired IPR&D charges													$ 50.0
NextCure, Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges												$ 28.1
Dicerna Pharmaceuticals Inc.
Business Acquisition [Line Items]
Acquired IPR&D charges											$ 148.7
Hydra Biosciences
Business Acquisition [Line Items]
Acquired IPR&D charges											$ 22.6