Financial Instruments Reconciliation of the Change in Level 3 Items (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jul. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	$ 28.7
Purchases	5.9
Transfer into (out of) Level 3	0
Settlements	(8.5)
Net unrealizrd gains (losses) included in earnings	0.8
Balance at April 30,2012	26.9
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	6.2
Purchases	1.1
Transfer into (out of) Level 3	0
Settlements	(1.3)
Net unrealizrd gains (losses) included in earnings	3.1
Balance at April 30,2012	9.1
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	4.8
Transfer into (out of) Level 3	0
Settlements	(7.2)
Net unrealized gains (losses) included in other comprehensive income	(2.3)
Balance at April 30,2012	13.6
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
Settlements	0
Net unrealizrd gains (losses) included in earnings	0
Balance at April 30,2012	$ 4.2