Retirement Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Service cost for benefits earned during the period	$ 5.6	$ 5.7	$ 4.6
Interest cost on projected benefit obligation	3.0	3.3	3.9
Expected return on plan assets	(4.2)	(3.9)	(4.6)
Amortization of prior service credit	(0.3)	(0.1)	(0.1)
Amortization of loss	1.5	1.4	0.6
Settlement loss	1.2	0.0	0.0
Net periodic benefit cost	$ 6.8	$ 6.4	$ 4.4