Employee Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Jan. 31, 2019	Jan. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 132.7	$ 116.5
Prior service cost (credit)	0.5	0.6
Total before tax	133.2	117.1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	(5.8)	1.3
Prior service cost (credit)	(1.0)	(1.7)
Total before tax	$ (6.8)	$ (0.4)