Recently Issued Accounting Standards (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Feb. 01, 2018	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Jan. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue		$ 611.7	$ 501.8	$ 1,171.6	$ 987.5
Capitalized contract cost		82.5		82.5
Accumulated deficit		(2,103.2)		(2,103.2)		$ (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	$ 179.4	$ (144.7)		$ (144.7)
Retained Earnings | Accounting Standards Update 2016-16
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative increase to accumulated deficit						$ 1.9