Financial Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2011 Investment	Oct. 31, 2010	Oct. 31, 2011 Investment	Oct. 31, 2010	Apr. 30, 2011	Jan. 31, 2011 Investment
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Available-for-sale securities gross gains (losses)	$ 0	$ 0	$ 0	$ 0
Estimated fair value	430.9		430.9
Securities in a continuous unrealized loss position for greater than 12 months	0		0			0
Notional amount of foreign currency option collar and forward contracts designated as cash flow hedges	401.9		401.9			345.5
Net loss expected to be recognized into earnings	3.6		3.6			0.8
Notional amount of foreign currency forward contracts not designated as cash flow hedges	24.1		24.1			56.1
Derivative financial instruments, maturities, minimum					1 month
Derivative financial instruments, maturities, maximum					12 months
Taxable auction rate securities | Minimum
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Marketable securities, contractual maturity	10 years		10 years
Long-term available-for-sale securities
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Estimated fair value	203.0		203.0			192.6
Long-term available-for-sale securities | Minimum
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Marketable securities, remaining maturities	12 months		12 months
Long-term available-for-sale securities | Taxable auction rate securities
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Estimated fair value	4.2		4.2			4.2
Short-term available-for-sale securities
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Estimated fair value	207.6		207.6			167.9
Short-term available-for-sale securities | Maximum
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Marketable securities, remaining maturities	12 months		12 months
Short-term available-for-sale securities | Mutual Funds
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Trading securities	32.7		32.7			31.3
Trading securities, unrealized gains	0.9		0.9			1.6
Trading securities, cost	$ 31.8		$ 31.8			$ 29.7