Quarterly report pursuant to Section 13 or 15(d)

Investment Income, Net (Details)

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Investment Income, Net (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Nov. 30, 2014
Nov. 30, 2013
Nov. 30, 2014
Nov. 30, 2013
Investment Income, Net [Abstract]        
Interest income on corporate funds $ 2.0us-gaap_InvestmentIncomeNonoperating $ 1.7us-gaap_InvestmentIncomeNonoperating $ 3.9us-gaap_InvestmentIncomeNonoperating $ 3.3us-gaap_InvestmentIncomeNonoperating
Interest expense (0.3)us-gaap_InterestExpenseOther (0.4)us-gaap_InterestExpenseOther (0.6)us-gaap_InterestExpenseOther (0.8)us-gaap_InterestExpenseOther
Net loss from equity-method investments (0.3)us-gaap_IncomeLossFromEquityMethodInvestments 0us-gaap_IncomeLossFromEquityMethodInvestments (0.5)us-gaap_IncomeLossFromEquityMethodInvestments 0us-gaap_IncomeLossFromEquityMethodInvestments
Investment income, net $ 1.4us-gaap_InterestIncomeExpenseNonoperatingNet $ 1.3us-gaap_InterestIncomeExpenseNonoperatingNet $ 2.8us-gaap_InterestIncomeExpenseNonoperatingNet $ 2.5us-gaap_InterestIncomeExpenseNonoperatingNet