Restructuring and other exit costs, net (Roll-forward)(Details) - USD ($) $ in Millions	6 Months Ended
	Jul. 31, 2018	Jul. 31, 2018	Jan. 31, 2018
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 55.5
Additions	36.3
Payments	(70.0)
Adjustments	(0.3)
Ending Balance	21.5
Current portion		$ 21.5	$ 55.5
Total Restructuring Reserve	55.5	21.5	55.5
Employee termination costs
Restructuring Reserve [Roll Forward]
Beginning Balance	53.0
Additions	33.5
Payments	(66.3)
Adjustments	(0.7)
Ending Balance	19.5
Total Restructuring Reserve	53.0	19.5	53.0
Lease termination and other exit costs
Restructuring Reserve [Roll Forward]
Beginning Balance	2.5
Additions	2.8
Payments	(3.7)
Adjustments	0.4
Ending Balance	2.0
Total Restructuring Reserve	$ 2.5	$ 2.0	$ 2.5