Pensions and Other Postretirement Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2024	Apr. 30, 2023	Apr. 30, 2022
Components of net periodic benefit cost:
Settlement loss (gain)	$ 3.2	$ 7.4	$ 10.8
Defined Benefit Pension Plans
Components of net periodic benefit cost:
Service cost	0.9	1.2	1.7
Interest cost	18.5	17.8	12.4
Expected return on plan assets	(16.1)	(15.4)	(15.9)
Amortization of prior service cost (credit)	0.1	0.7	0.9
Amortization of net actuarial loss (gain)	3.5	4.0	6.9
Curtailment loss (gain)	(1.2)	0.0	0.0
Settlement loss (gain)	3.2	7.4	10.8
Net periodic benefit cost	8.9	15.7	16.8
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	0.8	1.0	1.2
Interest cost	2.6	2.3	1.3
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service cost (credit)	(0.6)	(0.6)	(0.6)
Amortization of net actuarial loss (gain)	(1.5)	(1.2)	(0.4)
Curtailment loss (gain)	0.0	0.0	0.0
Settlement loss (gain)	0.0	0.0	0.0
Net periodic benefit cost	$ 1.3	$ 1.5	$ 1.5