Consolidated Statements of Comprehensive Income (Loss) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 44.4	$ 31.1	$ 102.4
Other comprehensive income (loss), net:
Foreign currency translation adjustments	(3.1)	(2.6)	(8.2)
Pension and post-retirement adjustments:
Amortization of prior service credit	(0.2)	(0.4)	(0.6)
Amortization of unrecognized gains and losses included in net periodic cost	13.5	11.8	(11.5)
Total other comprehensive income (loss)	10.2	8.8	(20.3)
Comprehensive income (loss)	$ 54.6	$ 39.9	$ 82.1