Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Schedule Of Asset Acquisition, By Acquisition [Line Items]
Effective Income Tax Rate Reconciliation, Intangible Asset Impairment, Percent			399.60%
Effective Income Tax Rate Reconciliation, Deduction, Percent				8.00%
Income Tax Expense (Benefit), Foreign-Derived Intangible Income		$ 29.9			$ 17.0
Effective Income Tax Rate Reconciliation Deduction, Foreign-Derived Intangible Income, Percent		5.60%		1.90%
Purchased technology
Schedule Of Asset Acquisition, By Acquisition [Line Items]
Impairment	$ 2,042.3
Intangible Asset Impairment
Schedule Of Asset Acquisition, By Acquisition [Line Items]
Deferred Income Tax Expense (Benefit)	$ (377.3)
Intellectual Property Election
Schedule Of Asset Acquisition, By Acquisition [Line Items]
Deferred Income Tax Expense (Benefit)				$ (95.7)
Valuation Allowance Release
Schedule Of Asset Acquisition, By Acquisition [Line Items]
Deferred Income Tax Expense (Benefit)				$ (30.3)