Pensions and Other Postretirement Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020
Components of net periodic benefit cost:
Settlement loss (gain)	$ 10.8	$ 35.5	$ 0.1
Defined Benefit Pension Plans
Components of net periodic benefit cost:
Service cost	1.7	1.8	1.6
Interest cost	12.4	14.4	20.9
Expected return on plan assets	(15.9)	(19.3)	(24.1)
Amortization of prior service cost (credit)	0.9	0.9	0.9
Amortization of net actuarial loss (gain)	6.9	10.9	7.9
Settlement loss (gain)	10.8	35.5	0.1
Termination benefit cost	0.0	0.0	0.2
Net periodic benefit cost	16.8	44.2	7.5
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	1.2	1.8	1.8
Interest cost	1.3	1.8	2.3
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service cost (credit)	(0.6)	(1.0)	(1.1)
Amortization of net actuarial loss (gain)	(0.4)	0.0	(0.3)
Settlement loss (gain)	0.0	0.0	0.0
Termination benefit cost	0.0	0.0	0.0
Net periodic benefit cost	$ 1.5	$ 2.6	$ 2.7