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Recently Issued Accounting Standards (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Feb. 01, 2018	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017	Jan. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue		$ 660.9	$ 515.3	$ 1,832.5	$ 1,502.8
Capitalized contract cost		75.8		75.8
Accumulated deficit adjustment		(2,189.9)		(2,189.9)		$ (2,084.9)
Accounting Standards Update 2014-09 \| Impact from the adoption of ASC 606 and 340-40
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue	$ 89.0
Capitalized contract cost	90.4
Accumulated deficit adjustment	$ 179.4	$ (138.7)		$ (138.7)
Accumulated deficit \| Accounting Standards Update 2016-16
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative increase to accumulated deficit						$ 1.9