Financial Instruments (Effects of Derivative Instruments on Condensed Consolidated Statements of Operations) (Details) - Foreign currency contracts - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in accumulated other comprehensive loss on derivatives (effective portion)	$ 6.4	$ (9.3)	$ 13.3	$ (11.4)
Amount and location of (loss) gain reclassified from accumulated other comprehensive loss into (loss) income (effective portion)	(5.1)	2.3	(4.3)	1.6
Designated as hedging instrument | Net revenue
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of (loss) gain reclassified from accumulated other comprehensive loss into (loss) income (effective portion)	(3.5)	2.8	(6.0)	4.8
Designated as hedging instrument | Operating expenses
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of (loss) gain reclassified from accumulated other comprehensive loss into (loss) income (effective portion)	(1.6)	(0.5)	1.7	(3.2)
Designated as hedging instrument | Interest and other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of gain (loss) recognized in (loss) income on derivatives (ineffective portion and amount excluded from effectiveness testing)	0.7	0.1	0.5	(0.1)
Derivatives not designated as hedging instruments | Interest and other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of gain (loss) recognized on derivatives in net (loss)	$ 1.4	$ (6.5)	$ 6.0	$ (8.3)