Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Income Tax Contingency [Line Items]
Deferred tax assets, other					$ 754.2
Deferred tax liabilities, other					$ 603.4
Decrease in unrecognized tax benefits is reasonably possible				$ 75.0
Denmark Manufacturing Operations
Income Tax Contingency [Line Items]
Tax expense on disposal group		$ 64.7	$ 64.7
TECFIDERA
Income Tax Contingency [Line Items]
Deferred tax assets, decrease in value	$ 1,627.9		1,627.9
Deferred tax liabilities, decrease in value	1,538.6		1,538.6
Income tax expense associated with reductions in deferred tax assets and liabilities	$ 33.3		$ 89.3