Fair Value Measurements Equity Investments and Other Financial Instruments - Fair Value Measurements of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 235.1	$ 41.1
Other current assets		14.4
Foreign currency forward and option contracts
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Derivative financial instruments net asset (liability)	0.3	(1.2)
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	235.1	41.1
Other current assets		14.4
Level 1 | Foreign currency forward and option contracts
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Derivative financial instruments net asset (liability)	0.0	0.0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0.0	0.0
Other current assets		0.0
Level 2 | Foreign currency forward and option contracts
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Derivative financial instruments net asset (liability)	0.3	(1.2)
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0.0	0.0
Other current assets		0.0
Level 3 | Foreign currency forward and option contracts
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Derivative financial instruments net asset (liability)	$ 0.0	$ 0.0