Financial Instruments Reconciliation of the Change in Level 3 Items (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Apr. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	$ 28.7
Purchases	2.9
Transfer into (out of) Level 3	0
Redemptions	0
Total unrealizrd gains (losses)	3.1
Balance at April 30,2012	34.7
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	6.2
Purchases	1.0
Transfer into (out of) Level 3	0
Redemptions	0
Total unrealizrd gains (losses)	4.4
Balance at April 30,2012	11.6
Convertible Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	18.3
Purchases	1.9
Transfer into (out of) Level 3	0
Redemptions	0
Total unrealizrd gains (losses)	(1.3)
Balance at April 30,2012	18.9
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	4.2
Purchases	0
Transfer into (out of) Level 3	0
Redemptions	0
Total unrealizrd gains (losses)	0
Balance at April 30,2012	$ 4.2