Pensions and Other Postretirement Benefits (Details 5) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2023	Apr. 30, 2022	Apr. 30, 2021
Components of net periodic benefit cost:
Settlement loss (gain)	$ 7.4	$ 10.8	$ 35.5
Pension Plan
Company's Canadian pension and other postretirement benefit plans
Benefit obligation at end of year	379.7	429.4	546.8
Fair value of plan assets at end of year	325.9	317.1	397.8
Funded status of the plans	(53.8)	(112.3)
Components of net periodic benefit cost:
Interest cost	17.8	12.4	14.4
Expected return on plan assets	(15.4)	(15.9)	(19.3)
Amortization of net actuarial loss (gain)	4.0	6.9	10.9
Settlement loss (gain)	7.4	10.8	35.5
Net periodic benefit cost (credit)	15.7	16.8	44.2
Change in plan assets:
Actual return on plan assets	(11.1)	(16.1)
Benefits paid	17.7	25.4
Settlement	(36.1)	(44.1)
Foreign currency translation adjustments	(0.4)	(0.4)
Other Postretirement Benefits Plan
Company's Canadian pension and other postretirement benefit plans
Benefit obligation at end of year	54.7	59.7	69.6
Fair value of plan assets at end of year	0.0	0.0	0.0
Funded status of the plans	(54.7)	(59.7)
Components of net periodic benefit cost:
Interest cost	2.3	1.3	1.8
Expected return on plan assets	0.0	0.0	0.0
Amortization of net actuarial loss (gain)	(1.2)	(0.4)	0.0
Settlement loss (gain)	0.0	0.0	0.0
Net periodic benefit cost (credit)	1.5	1.5	$ 2.6
Change in plan assets:
Actual return on plan assets	0.0	0.0
Benefits paid	4.3	4.1
Settlement	0.0	0.0
Foreign currency translation adjustments	0.0	0.0
CANADA | Pension Plan
Company's Canadian pension and other postretirement benefit plans
Benefit obligation at end of year	0.4	2.0
Fair value of plan assets at end of year	6.5	8.1
Funded status of the plans	6.1	6.1
Components of net periodic benefit cost:
Interest cost	0.1	0.1
Expected return on plan assets	(0.1)	0.1
Amortization of net actuarial loss (gain)	0.0	0.0
Settlement loss (gain)	0.7	0.0
Net periodic benefit cost (credit)	0.7	0.2
Change in plan assets:
Actual return on plan assets	0.1	0.3
Company contributions	0.1	(0.4)
Benefits paid	7.1	0.3
Settlement	(8.4)	0.0
Foreign currency translation adjustments	(0.4)	(0.4)
CANADA | Other Postretirement Benefits Plan
Company's Canadian pension and other postretirement benefit plans
Benefit obligation at end of year	3.9	4.9
Fair value of plan assets at end of year	0.0	0.0
Funded status of the plans	(3.9)	(4.9)
Components of net periodic benefit cost:
Interest cost	0.2	0.1
Expected return on plan assets	0.0	0.0
Amortization of net actuarial loss (gain)	(0.2)	(0.1)
Settlement loss (gain)	0.0	0.0
Net periodic benefit cost (credit)	0.0	0.0
Change in plan assets:
Actual return on plan assets	0.0	0.0
Company contributions	0.3	0.4
Benefits paid	0.3	0.4
Settlement	0.0	0.0
Foreign currency translation adjustments	$ 0.0	$ 0.0