Income Taxes (Details 4) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Reconciliation of unrecognized tax benefits
Balance at May 1,	$ 15.0	$ 32.3	$ 40.4
Increases:
Current year tax positions	1.4	0.9	1.1
Prior year tax positions	0.2	0.3	0.5
Decreases:
Settlement with tax authorities	0.0	9.0	3.0
Expiration of statute of limitations periods	3.5	9.5	6.7
Balance at April 30,	$ 13.1	$ 15.0	$ 32.3