Financial Instruments Reconciliation of the Change in Level 3 Items (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Oct. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31, 2014	$ 29.3
Purchases	0.5
Settlements	(4.4)
Net realized (losses)	(5.2)
Net unrealized (losses)	(3.3)
Balance at October 31, 2014	16.9
Derivative Contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31, 2014	9.1
Purchases	0.1
Settlements	(1.1)
Net realized (losses)	(3.0)
Net unrealized (losses)	(1.4)
Balance at October 31, 2014	3.7
Convertible Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 31, 2014	20.2
Purchases	0.4
Settlements	(3.3)
Net realized (losses)	(2.2)
Net unrealized (losses)	(1.9)
Balance at October 31, 2014	$ 13.2