Employee Benefit Plans - Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Earnings (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4.9	$ 4.2
Interest cost	7.4	8.1
Expected return on plan assets	(9.7)	(8.7)
Amortization of prior service credit	0.0	0.0
Amortization of net loss	5.6	2.6
Net expense	8.2	6.2
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	0.7
Interest cost	0.8	0.8
Expected return on plan assets	0.0	0.0
Amortization of prior service credit	(0.1)	(0.2)
Amortization of net loss	0.1	0.2
Net expense	$ 1.6	$ 1.5