Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI Activity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (56.5)	$ (80.9)	$ (55.7)	$ (94.2)
Other comprehensive income (loss) before reclassifications	1.7	2.2	(2.0)	6.0
Benefit from settlement (net of tax of $15.8)		23.8		33.0
Amortization of gains and losses (net of tax of $0.1)	0.2	0.5	0.6	1.4
Postretirement benefit plan remeasurement (net of tax)			2.0
Amortization of prior service credit	0.0		(0.1)
Other reclassifications (net of tax of $0.0)		(2.1)	0.6	(2.7)
Other comprehensive income (loss)	1.9	24.4	1.1	37.7
Ending balance	(54.6)	(56.5)	(54.6)	(56.5)
Settlement, Tax		23.8		33.0
Amortization, Tax	(0.2)	(0.5)	(0.6)	(1.4)
Remeasurement, Tax	0.0		2.0
Amortization of prior service credit, Tax	0.0		(0.1)
Other reclassifications, Tax	0.0	(2.1)	0.6	(2.7)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(45.6)	(41.5)	(41.9)	(45.3)
Other comprehensive income (loss) before reclassifications	1.7	2.2	(2.0)	6.0
Other comprehensive income (loss)	1.7	2.2	(2.0)	6.0
Ending balance	(43.9)	(39.3)	(43.9)	(39.3)
Retirement benefit plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(10.9)	(39.4)	(13.8)	(48.9)
Other comprehensive income (loss) before reclassifications	0.0	0.0	0.0	0.0
Benefit from settlement (net of tax of $15.8)		23.8		33.0
Amortization of gains and losses (net of tax of $0.1)	0.2	0.5	0.6	1.4
Postretirement benefit plan remeasurement (net of tax)			2.0
Amortization of prior service credit	0.0		(0.1)
Other reclassifications (net of tax of $0.0)		(2.1)	0.6	(2.7)
Other comprehensive income (loss)	0.2	22.2	3.1	31.7
Ending balance	$ (10.7)	$ (17.2)	$ (10.7)	$ (17.2)