Income Tax (Error Corrections) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jul. 31, 2016	Apr. 30, 2016	Jul. 31, 2015	Jul. 31, 2016	Jul. 31, 2015	Jan. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes	$ (25.2)	$ 14.4	$ (269.5)	$ (39.6)	$ (272.2)
Net loss	$ (98.2)	(167.7)	$ (268.6)	$ (265.9)	$ (249.5)
Basic net loss per share (in usd per share)	$ (0.44)		$ (1.18)	$ (1.19)	$ (1.10)
Current deferred tax liabilities			$ 9.5		$ 9.5
Accrued income taxes	$ 54.1		22.9	$ 54.1	22.9	$ 29.4
Long-term deferred tax liabilities	66.6		54.0	66.6	54.0	67.7
Long-term income tax payable	42.7	37.3	160.2	42.7	160.2	161.4
Retained earnings	$ (395.6)	(193.3)	131.3	$ (395.6)	131.3	$ (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 net loss per share (in usd per share)			$ (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
Retained earnings		$ (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 net loss per share (in usd 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
Retained earnings			$ (33.1)		$ (33.1)