Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 16.0	$ 17.6	$ 34.6	$ 25.8
(Loss) income before income taxes	(23.4)	$ (126.4)	(87.2)	$ (247.8)
Unrecognized tax benefits	343.1		343.1
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	310.0		310.0
Valuation Allowance of Deferred Tax Assets
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 33.1		$ 33.1