Derivative Instruments (Narrative) (Details) (USD $)	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Derivative Instruments [Abstract]
Net foreign currency exchange loss	$ 4,100,000	$ 6,700,000	$ 34,900,000
Notional amount of derivative financial instruments outstanding	$ 1,500,000,000	$ 1,300,000,000
Average maturities of derivatives, days	37	40