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, 2018	Apr. 30, 2017
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4.5	$ 4.7
Interest cost	7.6	8.0
Expected return on plan assets	(8.3)	(8.2)
Amortization of prior service cost (credit)	0.0	0.1
Amortization of net loss	3.3	3.5
Net periodic benefit cost	7.1	8.1
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.7	0.7
Interest cost	0.8	0.8
Expected return on plan assets	0.0	0.0
Amortization of prior service cost (credit)	(0.2)	(0.2)
Amortization of net loss	0.0	0.0
Net periodic benefit cost	$ 1.3	$ 1.3