Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI Activity (Details) - USD ($) $ in Millions	6 Months Ended
	Nov. 30, 2017	Nov. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (94.2)	$ (86.7)
Other comprehensive income (loss) before reclassifications	3.1	(7.0)
Less: amount reclassified from Accumulated other comprehensive income (loss) (net of tax of $6.4)	10.2	1.4
Other comprehensive income (loss)	13.3	(5.6)
Ending balance	(80.9)	(92.3)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(45.3)	(40.0)
Other comprehensive income (loss) before reclassifications	3.8	(7.0)
Less: amount reclassified from Accumulated other comprehensive income (loss) (net of tax of $6.4)	0.0	0.0
Other comprehensive income (loss)	3.8	(7.0)
Ending balance	(41.5)	(47.0)
Retirement benefit plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(48.9)	(46.7)
Other comprehensive income (loss) before reclassifications	(0.7)	0.0
Less: amount reclassified from Accumulated other comprehensive income (loss) (net of tax of $6.4)	10.2	1.4
Other comprehensive income (loss)	9.5	1.4
Ending balance	$ (39.4)	$ (45.3)