Available-For-Sale Securities (Detail) (USD $) In Millions, unless otherwise specified	Oct. 31, 2011	Jan. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 430.9
Short-term available-for-sale securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	207.5	167.8
Gross unrealized gains	0.1	0.1
Estimated Fair Value	207.6	167.9
Short-term available-for-sale securities | Commercial paper and corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	126.9	47.6
Gross unrealized gains	0.1	0.1
Estimated Fair Value	127.0	47.7
Short-term available-for-sale securities | U.S. Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15.4	26.0
Estimated Fair Value	15.4	26.0
Short-term available-for-sale securities | Certificates of deposit and time deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4.8	29.0
Estimated Fair Value	4.8	29.0
Short-term available-for-sale securities | US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	50.1	47.2
Estimated Fair Value	50.1	47.2
Short-term available-for-sale securities | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10.0	8.6
Estimated Fair Value	10.0	8.6
Short-term available-for-sale securities | Other
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0.3	0.3
Estimated Fair Value	0.3	0.3
Short-term available-for-sale securities | Sovereign Debt
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		9.1
Estimated Fair Value		9.1
Long-term available-for-sale securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	202.3	190.8
Gross unrealized gains	1.4	1.9
Gross unrealized losses	(0.7)	(0.1)
Estimated Fair Value	203.0	192.6
Long-term available-for-sale securities | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	131.1	152.6
Gross unrealized gains	1.0	1.5
Gross unrealized losses	(0.6)	(0.1)
Estimated Fair Value	131.5	154.0
Long-term available-for-sale securities | U.S. Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24.4	12.7
Gross unrealized gains	0.3	0.1
Estimated Fair Value	24.7	12.8
Long-term available-for-sale securities | US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27.2	12.7
Gross unrealized gains		0.2
Gross unrealized losses	(0.1)
Estimated Fair Value	27.1	12.9
Long-term available-for-sale securities | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3.0	4.7
Gross unrealized gains	0.1
Estimated Fair Value	3.1	4.7
Long-term available-for-sale securities | Taxable auction rate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4.2	4.2
Estimated Fair Value	4.2	4.2
Long-term available-for-sale securities | Convertible Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12.4
Estimated Fair Value	12.4
Long-term available-for-sale securities | Sovereign Debt
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		3.9
Gross unrealized gains		0.1
Estimated Fair Value		$ 4.0