Accumulated Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2017	Feb. 29, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax effect	$ 8.4	$ 9.4	$ (10.8)	$ (1.5)
Net income (loss)	(15.4)	(9.0)	12.9	6.5
Amount reclassified from Accumulated other comprehensive income (loss) | Retirement benefit plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost (credit)	0.0	0.0	0.0	0.0
Amortization of unrecognized gain (loss) included in net periodic cost (credit)	1.0	1.1	3.1	3.3
Less: Tax effect	(0.3)	(0.3)	(1.0)	(1.0)
Net income (loss)	$ 0.7	$ 0.8	$ 2.1	$ 2.3