Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended
	May 31, 2018	Oct. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Variable Interest Entity [Line Items]
Payments to Noncontrolling Interests					$ 70.9	$ (4.3)
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities			$ 21.9		21.9		$ 22.7
Loss on equity method investment					$ 14.7	63.5
Neurimmune
Variable Interest Entity [Line Items]
Collaboration agreement term					12 years
Research and development costs, percentage					100.00%
Payments to Noncontrolling Interests	$ 50.0	$ 150.0
Reduction in royalty rate payable on commercial sales		15.00%
Additional reduction in royalty rate payable on commercial sales	5.00%
Regulatory Milestones [Member] | Neurimmune
Variable Interest Entity [Line Items]
Potential Future Milestone Payments Commitment To Third Party Approximately							75.0
Regulatory Approval Milestone [Member] | Neurimmune
Variable Interest Entity [Line Items]
Potential Future Milestone Payments Commitment To Third Party Approximately							$ 100.0
Eisai
Variable Interest Entity [Line Items]
Loss on equity method investment			$ 0.0	$ 0.0	$ 33.8	$ 0.0
Percentage of future development costs related to Eisai					45.00%