Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Nov. 30, 2015	Aug. 31, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	$ (40.0)	$ (40.4)	$ (37.9)	$ (40.4)	$ (29.3)
Other comprehensive income (loss) before reclassifications from AOCL	0.8		(14.9)	1.0	(23.6)
Amounts reclassified from AOCL	0.3			0.5	0.1
Total other comprehensive income (loss)	1.1		(14.9)	1.5	(23.5)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(38.9)	(40.0)	(52.8)	(38.9)	(52.8)
Currency Translation Adjustments
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	(0.9)	0.9	(0.3)	0.9	8.7
Reclassification within AOCL				(2.0)
Other comprehensive income (loss) before reclassifications from AOCL	0.8		(14.8)	1.0	(23.8)
Total other comprehensive income (loss)	0.8		(14.8)	1.0	(23.8)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(0.1)	(0.9)	(15.1)	(0.1)	(15.1)
Pensions Plans
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	(39.1)	(41.3)	(35.3)	(41.3)	(35.4)
Reclassification within AOCL				2.0
Amounts reclassified from AOCL	0.3			0.5	0.1
Total other comprehensive income (loss)	0.3			0.5	0.1
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	$ (38.8)	$ (39.1)	(35.3)	$ (38.8)	(35.3)
Derivative Instruments
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance			(2.3)		(2.6)
Other comprehensive income (loss) before reclassifications from AOCL			(0.1)		0.2
Total other comprehensive income (loss)			(0.1)		0.2
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance			$ (2.4)		$ (2.4)