Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net foreign currency exchange gain (loss)	$ 23.7	$ (6.6)	$ 22.7	$ 0.8
Notional amount of derivative financial instruments outstanding	$ 1,200.0	$ 500.0	$ 1,000.0	$ 500.0
Average maturities of derivatives, days	36 days	32 days	36 days	31 days