Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Income Tax Contingency [Line Items]
Deferred tax assets, net	$ 500.0		$ 500.0
Deferred tax assets, gross	875.0		875.0
Deferred tax assets, unrecognized tax benefit	375.0		375.0
Decrease in unrecognized tax benefits is reasonably possible					$ 20.0
TECFIDERA
Income Tax Contingency [Line Items]
Deferred tax assets, decrease in value	1,700.0		1,700.0
Deferred tax liabilities, decrease in value	1,600.0		1,600.0
Deferred tax asset, increase (decrease) in value	$ 92.6		$ 92.6
Deferred tax liabilities, increase (decrease) in value		$ 88.7		$ 88.7