Financial Instruments - Reconciliation of the Change in Level 3 Items (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 29.3	$ 32.4
Purchases	0.7	4.4
Settlements	(3.8)	(4.0)
Losses included in earnings	(20.8)	(3.1)	[1]
Gains included in OCI	0.6	(0.4)	[1]
Ending Balance	6.0	29.3
Derivative Contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	9.1	10.7
Purchases	0.1	1.3
Settlements	(0.8)	0
Losses included in earnings	(7.5)	(2.9)	[1]
Gains included in OCI	0	0	[1]
Ending Balance	0.9	9.1
Convertible Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	20.2	17.5
Purchases	0.6	3.1
Settlements	(3.0)	0
Losses included in earnings	(13.3)	0	[1]
Gains included in OCI	0.6	(0.4)	[1]
Ending Balance	5.1	20.2
Taxable Auction-Rate Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0	4.2
Purchases	0	0
Settlements	0	(4.0)
Losses included in earnings	0	(0.2)	[1]
Gains included in OCI	0
Ending Balance	$ 0	$ 0

[1] For comparability, the presentation of prior period balances were adjusted to align with current year presentation.