Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2018	Aug. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (55.7)	$ (94.2)
Other comprehensive income (loss) before reclassifications	(3.1)	3.7
Amortization (net of tax of $0.0)	(0.2)	(0.5)
Other comprehensive income (loss)	(2.9)	4.2
Ending balance	(58.6)	(90.0)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(41.9)	(45.3)
Other comprehensive income (loss) before reclassifications	(3.1)	3.7
Other comprehensive income (loss)	(3.1)	3.7
Ending balance	(45.0)	(41.6)
Retirement benefit plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(13.8)	(48.9)
Other comprehensive income (loss) before reclassifications	0.0	0.0
Amortization (net of tax of $0.0)	(0.2)	(0.5)
Other comprehensive income (loss)	0.2	0.5
Ending balance	(13.6)	(48.4)
Amortization, Tax	$ 0.0	$ (0.1)