Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (5.0)	$ 52.3	$ 40.5
Other comprehensive income (loss), net:
Foreign currency translation adjustments (net of tax)	3.4	(5.3)	(8.1)
Pension and postretirement adjustments (net of tax)	35.1	(2.2)	(1.6)
Total other comprehensive income (loss)	38.5	(7.5)	(9.7)
Comprehensive income (loss)	$ 33.5	$ 44.8	$ 30.8