Goodwill and Other Intangibles - Schedule of other intangible assets subject to amortization (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Aug. 31, 2019	Aug. 31, 2018	May 31, 2018	May 31, 2014	May 31, 2019
Finite-lived Intangible Assets [Roll Forward]
Beginning balance other intangibles subject to amortization	$ 12.2		$ 10.1
Additions	0.0	$ 0.5	4.5
Amortization expense	(0.8)	(0.7)	(2.8)
Foreign currency translation	(0.2)	0.0	$ (0.2)
Other	0.0	0.0		$ 0.6
Total other intangibles subject to amortization, net of accumulated amortization of $24.8, $24.1 and $22.5, respectively	11.2	9.9
Accumulated amortization of intangible assets	27.7	24.8			$ 26.9
Total other intangibles not subject to amortization	2.1	2.1			2.1
Total other intangibles	$ 13.3	$ 12.0			$ 14.3