Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI Activity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 1,196.7	$ 1,209.4	$ 1,272.8	$ 1,320.8
Other comprehensive income (loss) before reclassifications	3.9	(0.6)	1.9	(3.7)
Amortization of gains and losses, net of tax	0.3	0.2	0.5	0.4
Postretirement benefit plan remeasurement (net of tax of $0.7)		2.0		2.0
Amortization of prior service credit	(0.1)	(0.1)	(0.1)	(0.1)
Other reclassifications (net of tax of $0)		0.6		0.6
Other comprehensive income (loss)	4.1	2.1	2.3	(0.8)
Ending Balance	1,261.3	1,284.6	1,261.3	1,284.6
Amortization, Tax	0.0	0.0	0.0	0.0
Postretirement benefit plan remeasurement, tax	0.7		0.7
Amortization of prior service credit, Tax	0.0	0.0	0.0	0.0
Other reclassifications, tax	0.2	0.2		0.2
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(61.5)	(58.6)	(59.7)	(55.7)
Ending Balance	(57.4)	(56.5)	(57.4)	(56.5)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(49.1)	(45.0)	(47.1)	(41.9)
Other comprehensive income (loss) before reclassifications	3.9	(0.6)	1.9	(3.7)
Other comprehensive income (loss)	3.9	(0.6)	1.9	(3.7)
Ending Balance	(45.2)	(45.6)	(45.2)	(45.6)
Retirement benefit plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(12.4)	(13.6)	(12.6)	(13.8)
Other comprehensive income (loss) before reclassifications	0.0	0.0	0.0	0.0
Amortization of gains and losses, net of tax	0.3	0.2	0.5	0.4
Postretirement benefit plan remeasurement (net of tax of $0.7)		2.0		2.0
Amortization of prior service credit	(0.1)	(0.1)	(0.1)	(0.1)
Other reclassifications (net of tax of $0)		0.6		0.6
Other comprehensive income (loss)	0.2	2.7	0.4	2.9
Ending Balance	$ (12.2)	$ (10.9)	$ (12.2)	$ (10.9)