Derivative Instruments (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net foreign currency exchange loss	$ 3,600,000	$ 8,200,000	$ 20,500,000	$ (11,700,000)
Notional amount of derivative financial instruments outstanding	$ 2,000,000,000	$ 1,600,000,000
Average maturities of derivatives, days	29 days	28 days