Financial Instruments Reconciliation of the Change in Level 3 Items (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Oct. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	$ 28.7
Purchases	9.0
Transfer into (out of) Level 3	0
Settlements	(8.5)
Net unrealizrd gains (losses) included in earnings	1.7
Balance at April 30,2012	30.9
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31,2012	6.2
Purchases	2.0
Transfer into (out of) Level 3	0
Settlements	(1.3)
Net unrealizrd gains (losses) included in earnings	3.7
Balance at April 30,2012	10.6
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	7.0
Transfer into (out of) Level 3	0
Settlements	(7.2)
Net unrealized gains (losses) included in other comprehensive income	(2.0)
Balance at April 30,2012	16.1
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