Restructuring charges and other facility exit costs, net (Details) - USD ($) $ in Millions	9 Months Ended
	Oct. 31, 2017	Oct. 31, 2017	Jan. 31, 2017
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 7.5
Additions	0.5
Payments	(5.1)
Adjustments	(0.3)
Ending Balance	2.6
Current portion		$ 2.4	$ 5.9
Non-current portion		0.2	1.6
Total Restructuring Reserve	7.5	2.6	7.5
Lease termination and other exit costs
Restructuring Reserve [Roll Forward]
Beginning Balance	4.5
Additions	0.3
Payments	(2.3)
Adjustments	(0.2)
Ending Balance	2.3
Total Restructuring Reserve	4.5	2.3	4.5
Fiscal 2017 Plan | Employee termination costs
Restructuring Reserve [Roll Forward]
Beginning Balance	1.1
Additions	0.1
Payments	(1.4)
Adjustments	0.2
Ending Balance	0.0
Total Restructuring Reserve	1.1	0.0	1.1
Fiscal 2017 Plan | Lease termination and other exit costs
Restructuring Reserve [Roll Forward]
Beginning Balance	1.9
Additions	0.1
Payments	(1.4)
Adjustments	(0.3)
Ending Balance	0.3
Total Restructuring Reserve	$ 1.9	$ 0.3	$ 1.9