Derivative Instruments (Narrative) (Details) (USD $)	3 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net foreign currency exchange loss	$ 16,900,000	$ (3,500,000)
Notional amount of derivative financial instruments outstanding	$ 2,100,000,000	$ 1,700,000,000
Average maturities of derivatives, days	28 days	28 days