Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net foreign currency exchange gain/loss	$ 21.5	$ (0.3)	$ 20.9	$ 22.4
Notional amount of derivative financial instruments outstanding	$ 1,500.0	$ 900.0	$ 1,400.0	$ 1,000.0
Average maturities of derivatives, days	24 days	28 days	27 days	33 days