Accumulated Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax effect	$ 37.9	$ 23.9
Net income (loss)	(63.7)	(39.6)
Amount reclassified from Accumulated other comprehensive income (loss) | Retirement benefit plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrecognized gain (loss) included in net periodic benefit (cost)	0.6	1.0
Less: Tax effect	(0.1)	(0.3)
Net income (loss)	$ 0.5	$ 0.7