Goodwill and Other Intangibles - Schedule of activity in goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Aug. 31, 2019	Aug. 31, 2018	May 31, 2018	May 31, 2019	May 31, 2017
Goodwill [Roll Forward]
Gross goodwill				$ 164.8	$ 158.8
Accumulated impairment				$ (39.6)	$ (39.6)
Beginning balance	$ 125.2		$ 119.2
Additions	0.0	$ 0.0	6.3
Foreign currency translation	(0.2)	(0.1)	$ (0.3)
Ending balance	$ 125.0	$ 119.1

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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