Retirement Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Retirement Benefits [Abstract]
Service cost for benefits earned during the period	$ 5.2	$ 5.6	$ 5.7
Interest cost on projected benefit obligation	2.7	3.0	3.3
Expected return on plan assets	(3.9)	(4.2)	(3.9)
Amortization of prior service credit	(0.3)	(0.3)	(0.1)
Amortization of loss	1.2	1.5	1.4
Settlement loss	1.9	1.2	0.0
Curtailment gain	(0.1)	0.0	0.0
Net periodic benefit cost	$ 6.7	$ 6.8	$ 6.4