Goodwill and Other Intangibles - Schedule of other intangible assets subject to amortization (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	May 31, 2020
Finite-lived Intangible Assets [Roll Forward]
Beginning balance other intangibles subject to amortization	$ 10.5	$ 12.2	$ 12.2
Additions	0.0	0.0	1.6
Amortization expense	(0.6)	(0.8)	(3.2)
Foreign currency translation	0.3	(0.2)	(0.1)
Total other intangibles subject to amortization, net of accumulated amortization of $24.8, $24.1 and $22.5, respectively	10.2	11.2	10.5
Accumulated amortization of intangible assets	30.7	27.7	30.1
Total other intangibles not subject to amortization	2.1	2.1	2.1
Total other intangibles	$ 12.3	$ 13.3	$ 12.6