Debt, Derivatives and Hedging Activities (Details) - USD ($)	3 Months Ended
	Aug. 31, 2015	Aug. 31, 2014	May. 31, 2015
Line of Credit Facility [Line Items]
Commercial paper program availability	$ 300,000,000
Revolving credit facility, maximum borrowing capacity with accordion feature	450,000,000
Revolving credit facility amount outstanding	0		$ 0
Amortization of interest rate lock agreements	488,000	$ 488,000
Level 2 | Foreign Exchange Forward | Fair Value, Measurements, Recurring
Line of Credit Facility [Line Items]
Current accrued liabilities for foreign currency forward contracts	0
Unsecured Debt
Line of Credit Facility [Line Items]
Long-term debt, carrying amount	1,300,000,000		1,300,000,000
Long-term debt, fair value	$ 1,415,100,000		$ 1,418,600,000