Income Tax (Error Corrections) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended
	Oct. 31, 2016	Apr. 30, 2016	Oct. 31, 2015	Jul. 31, 2015	Jul. 31, 2015	Oct. 31, 2016	Oct. 31, 2015	Jan. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes	$ (13.5)	$ 14.4	$ (21.3)	$ (269.5)	$ (272.2)	$ (53.1)	$ (293.5)
Net loss	(142.8)	$ (167.7)	$ (43.8)	$ (268.6)	$ (249.5)	(408.7)	$ (293.3)
Basic and diluted net loss per share (in dollars per share)		$ (0.75)		$ (1.18)	$ (1.10)
Current deferred tax liabilities				$ 9.5	$ 9.5
Accrued income taxes	85.9			22.9	22.9	85.9		$ 29.4
Long-term deferred tax liabilities	75.9			54.0	54.0	75.9		67.7
Long-term income tax payable	40.0	$ 37.3		160.2	160.2	40.0		161.4
Accumulated deficit	$ (634.7)	(193.3)		131.3	131.3	$ (634.7)		$ (80.8)
Scenario, Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes		14.4		(236.4)	(239.1)
Net loss		$ (173.0)		$ (235.5)	$ (216.4)
Basic and diluted net loss per share (in dollars per share)		$ (0.77)		$ (1.04)	$ (0.95)
Current deferred tax liabilities				$ 8.3	$ 8.3
Accrued income taxes				52.3	52.3
Long-term deferred tax liabilities				28.9	28.9
Long-term income tax payable		$ 153.8		124.0	124.0
Accumulated deficit		$ (308.2)		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 and diluted net loss per share (in dollars per share)				$ (0.14)	$ (0.15)
Current deferred tax liabilities				$ 1.2	$ 1.2
Accrued income taxes				(29.4)	(29.4)
Long-term deferred tax liabilities				25.1	25.1
Long-term income tax payable				36.2	36.2
Accumulated deficit				$ (33.1)	$ (33.1)