Restructuring and other exit costs, net (Roll-forward) (Details) - USD ($) $ in Millions	9 Months Ended
	Oct. 31, 2018	Oct. 31, 2018	Jan. 31, 2018
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 55.5
Additions	40.5
Payments	(89.1)
Adjustments	(0.1)
Ending Balance	6.8
Current portion		$ 6.8	$ 55.5
Total Restructuring Reserve	55.5	6.8	55.5
Employee termination costs
Restructuring Reserve [Roll Forward]
Beginning Balance	53.0
Additions	37.4
Payments	(83.6)
Adjustments	(0.2)
Ending Balance	6.6
Total Restructuring Reserve	53.0	6.6	53.0
Lease termination and other exit costs
Restructuring Reserve [Roll Forward]
Beginning Balance	2.5
Additions	3.1
Payments	(5.5)
Adjustments	0.1
Ending Balance	0.2
Total Restructuring Reserve	$ 2.5	$ 0.2	$ 2.5