Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 8.6	$ 13.5	$ 34.4	$ 53.1
(Loss) income before income taxes	(111.2)	$ (129.3)	(359.0)	$ (355.6)
Unrecognized tax benefits	291.4		291.4
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	277.4		277.4
Valuation Allowance of Deferred Tax Assets
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 30.8		$ 30.8