Pensions and Other Postretirement Benefits (Details 5) - 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
Pension Plan
Company's Canadian pension and other postretirement benefit plans
Benefit obligation at end of year	429.4	546.8	652.3
Fair value of plan assets at end of year	317.1	397.8	471.6
Funded status of the plans	(112.3)	(149.0)
Components of net periodic benefit cost:
Interest cost	12.4	14.4	20.9
Expected return on plan assets	(15.9)	(19.3)	(24.1)
Amortization of net actuarial loss (gain)	6.9	10.9	7.9
Settlement loss (gain)	10.8	35.5	0.1
Net periodic benefit cost (credit)	16.8	44.2	7.5
Change in plan assets:
Actual return on plan assets	(16.1)	44.5
Benefits paid	(25.4)	(35.9)
Settlement	(44.1)	(101.2)
Foreign currency translation adjustments	(0.4)	5.7
Other Postretirement Benefits Plan
Company's Canadian pension and other postretirement benefit plans
Benefit obligation at end of year	59.7	69.6	74.5
Fair value of plan assets at end of year	0.0	0.0	0.0
Funded status of the plans	(59.7)	(69.6)
Components of net periodic benefit cost:
Interest cost	1.3	1.8	2.3
Expected return on plan assets	0.0	0.0	0.0
Amortization of net actuarial loss (gain)	(0.4)	0.0	(0.3)
Settlement loss (gain)	0.0	0.0	0.0
Net periodic benefit cost (credit)	1.5	2.6	$ 2.7
Change in plan assets:
Actual return on plan assets	0.0	0.0
Benefits paid	(4.1)	(3.4)
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	2.0	2.0
Fair value of plan assets at end of year	8.1	8.9
Funded status of the plans	6.1	6.9
Components of net periodic benefit cost:
Interest cost	0.1	0.9
Expected return on plan assets	0.1	(1.1)
Amortization of net actuarial loss (gain)	0.0	0.4
Settlement loss (gain)	0.0	29.6
Net periodic benefit cost (credit)	0.2	29.8
Change in plan assets:
Actual return on plan assets	0.3	0.9
Company contributions	(0.4)	(1.1)
Benefits paid	(0.3)	(4.4)
Settlement	0.0	(83.2)
Foreign currency translation adjustments	(0.4)	5.7
CANADA | Other Postretirement Benefits Plan
Company's Canadian pension and other postretirement benefit plans
Benefit obligation at end of year	4.9	6.1
Fair value of plan assets at end of year	0.0	0.0
Funded status of the plans	(4.9)	(6.1)
Components of net periodic benefit cost:
Interest cost	0.1	0.2
Expected return on plan assets	0.0	0.0
Amortization of net actuarial loss (gain)	(0.1)	0.0
Settlement loss (gain)	0.0	0.0
Net periodic benefit cost (credit)	0.0	0.2
Change in plan assets:
Actual return on plan assets	0.0	0.0
Company contributions	0.4	0.4
Benefits paid	(0.4)	(0.4)
Settlement	0.0	0.0
Foreign currency translation adjustments	$ 0.0	$ 0.0