Pensions and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2022	Jul. 31, 2021
Components of net periodic benefit cost
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 70.0
Defined Benefit Plan, Plan Assets, Benefits Paid	0.7
Defined Benefit Pension Plans
Components of net periodic benefit cost
Service cost	0.3	$ 0.4
Interest cost	4.4	3.2
Expected return on plan assets	(4.0)	(4.1)
Amortization of net actuarial loss (gain)	1.0	1.7
Amortization of prior service cost (credit)	0.1	0.2
Settlement loss (gain)	0.0	3.7
Net periodic benefit cost	1.8	5.1
Other Postretirement Benefits
Components of net periodic benefit cost
Service cost	0.2	0.3
Interest cost	0.6	0.4
Expected return on plan assets	0.0	0.0
Amortization of net actuarial loss (gain)	(0.3)	(0.1)
Amortization of prior service cost (credit)	(0.1)	(0.2)
Settlement loss (gain)	0.0	0.0
Net periodic benefit cost	$ 0.4	$ 0.4