Employee Benefit Plans - Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Earnings (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4.3	$ 4.4	$ 8.5	$ 8.9
Interest cost	8.2	7.8	16.3	15.4
Expected return on plan assets	(9.7)	(8.4)	(18.4)	(16.7)
Amortization of prior service cost (credit)	0.0	0.0	0.0	0.0
Amortization of net loss	3.0	4.2	5.6	7.5
Net periodic benefit cost	5.8	8.0	12.0	15.1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.6	0.7	1.3	1.5
Interest cost	0.9	0.8	1.7	1.6
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service cost (credit)	(0.1)	(0.2)	(0.3)	(0.4)
Amortization of net loss	(0.2)	0.0	0.0	0.0
Net periodic benefit cost	$ 1.2	$ 1.3	2.7	$ 2.7
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Voluntary cash contribution			$ 30.0