Reconciliation of the Change in Level 3 Items (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 4.2	$ 17.6
Purchases	24.5
Transfers into (out of) Level 3	0	0
Redemptions	0	(15.1)
Total realized/unrealized gains (losses) included in earnings	0	1.7
Ending Balance	28.7	4.2
Derivative
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	0	0
Purchases	6.2
Transfers into (out of) Level 3	0	0
Redemptions	0	0
Total realized/unrealized gains (losses) included in earnings	0	0
Ending Balance	6.2	0
Convertible Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	0	0
Purchases	18.3
Transfers into (out of) Level 3	0	0
Redemptions	0	0
Total realized/unrealized gains (losses) included in earnings	0	0
Ending Balance	18.3	0
Money Market Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	0	10.0
Purchases	0
Transfers into (out of) Level 3	0	0
Redemptions	0	(11.7)
Total realized/unrealized gains (losses) included in earnings	0	1.7
Ending Balance	0	0
Taxable auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	4.2	7.6
Purchases	0
Transfers into (out of) Level 3	0	0
Redemptions	0	(3.4)
Total realized/unrealized gains (losses) included in earnings	0	0
Ending Balance	$ 4.2	$ 4.2