Income Tax (Error Corrections) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended
	Oct. 31, 2015	Jul. 31, 2015	Oct. 31, 2014	Jul. 31, 2015	Oct. 31, 2015	Oct. 31, 2014	Jan. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes	$ (21.3)	$ (269.5)	$ (0.9)	$ (272.2)	$ (293.5)	$ (19.8)
Net loss	$ (43.8)	$ (268.6)	$ 10.7	$ (249.5)	$ (293.3)	$ 70.3
Basic net loss per share (in usd per share)	$ (0.19)	$ (1.18)	$ 0.05	$ (1.10)	$ (1.29)	$ 0.31
Current deferred tax liabilities (1)		$ 9.5		$ 9.5
Accrued income taxes	$ 28.2	22.9		22.9	$ 28.2		$ 28.2
Long term deferred income taxes	54.9	54.0		54.0	54.9		0.0
Long term income taxes payable	163.8	160.2		160.2	163.8		158.8
Retained earnings	$ 9.7	131.3		131.3	$ 9.7		$ 499.4
Scenario, Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes		(236.4)		(239.1)
Net loss		$ (235.5)		$ (216.4)
Basic net loss per share (in usd per share)		$ (1.04)		$ (0.95)
Current deferred tax liabilities (1)		$ 8.3		$ 8.3
Accrued income taxes		52.3		52.3
Long term deferred income taxes		28.9		28.9
Long term income taxes payable		124.0		124.0
Retained earnings		164.4		164.4
Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes		(33.1)		(33.1)
Net loss		$ (33.1)		$ (33.1)
Basic net loss per share (in usd per share)		$ (0.14)		$ (0.15)
Current deferred tax liabilities (1)		$ 1.2		$ 1.2
Accrued income taxes		(29.4)		(29.4)
Long term deferred income taxes		25.1		25.1
Long term income taxes payable		36.2		36.2
Retained earnings		$ (33.1)		$ (33.1)