Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Nov. 30, 2023	Aug. 31, 2023	Nov. 30, 2022	Aug. 31, 2022	Nov. 30, 2023	Nov. 30, 2022
Accumulated Other Comprehensive Loss
Beginning Balance	$ (8.1)	$ (23.5)	$ (22.7)	$ (19.6)	$ (23.5)	$ (19.6)
Other comprehensive income (loss) before reclassifications	(0.4)		(0.3)		0.1	(3.6)
Amounts reclassified from AOCL			0.2		14.9	0.4
Total other comprehensive income (loss)	(0.4)	15.4	(0.1)	(3.1)	15.0	(3.2)
Ending Balance	(8.5)	(8.1)	(22.8)	(22.7)	(8.5)	(22.8)
Currency Translation Adjustments
Accumulated Other Comprehensive Loss
Beginning Balance	(5.2)	(5.7)	(6.1)	(2.8)	(5.7)	(2.8)
Other comprehensive income (loss) before reclassifications	(0.4)		(0.3)		0.1	(3.6)
Total other comprehensive income (loss)	(0.4)		(0.3)		0.1	(3.6)
Ending Balance	(5.6)	(5.2)	(6.4)	(6.1)	(5.6)	(6.4)
Pensions Plans
Accumulated Other Comprehensive Loss
Beginning Balance	(2.9)	(17.8)	(16.6)	(16.8)	(17.8)	(16.8)
Amounts reclassified from AOCL			0.2		14.9	0.4
Total other comprehensive income (loss)			0.2		14.9	0.4
Ending Balance	$ (2.9)	$ (2.9)	$ (16.4)	$ (16.6)	$ (2.9)	$ (16.4)