Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 17.6	$ 25.2	$ 25.8	$ 39.6
(Loss) income before income taxes	(126.4)	$ (73.0)	(247.8)	$ (226.3)
Unrecognized tax benefits	267.5		267.5
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	253.6		253.6
Valuation Allowance of Deferred Tax Assets
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 32.8		$ 32.8