Financial Instruments and Risk Management (Effect of Derivative Instruments on the Condensed Consolidated Balance Sheets Fair Values of Derivative Instruments Derivatives Not Designated As Hedging Instrument) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Fair value of financial instruments	$ 40.1	$ 33.8
Fair value of financial instruments	9.7	17.3
Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair value of financial instruments	16.8	30.2
Not Designated as Hedging Instruments | Prepaid expenses and other current assets | Foreign currency forward contracts
Derivatives, Fair Value [Line Items]
Fair value of financial instruments	16.8	30.2
Not Designated as Hedging Instruments | Other current liabilities | Foreign currency forward contracts
Derivatives, Fair Value [Line Items]
Fair value of financial instruments	$ 9.7	$ 17.3