Financial Instruments - Reconciliation of the Change in Level 3 Items (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Jan. 31, 2014	Jan. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 32.4	$ 28.7
Purchases	4.4	9.0
Settlements	(4.0)	(8.5)
Net realized losses	(0.2)
Total unrealized gains (losses)	(3.3)	3.2
Ending Balance	29.3	32.4
Derivative Contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	10.7	6.2
Purchases	1.3	2.0
Settlements	0	(1.3)
Net realized losses	0
Total unrealized gains (losses)	(2.9)	3.8
Ending Balance	9.1	10.7
Convertible Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	17.5	18.3
Purchases	3.1	7.0
Settlements	0	(7.2)
Net realized losses	0
Total unrealized gains (losses)	(0.4)	(0.6)
Ending Balance	20.2	17.5
Taxable Auction-Rate Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	4.2	4.2
Purchases	0	0
Settlements	(4.0)	0
Net realized losses	(0.2)
Total unrealized gains (losses)	0	0
Ending Balance	$ 0	$ 4.2