Commitments and Contingencies (Details) - Line of Credit [Member] $ in Millions	6 Months Ended
	Nov. 30, 2015 USD ($)
JP Morgan Chase Bank, N.A. [Member]
Lines of credit
Amount available	$ 350
Expiration date	Feb. 28, 2016
Bank of America, N.A. [Member]
Lines of credit
Amount available	$ 250
Expiration date	Feb. 28, 2016
PNC Bank, National Association [Member]
Lines of credit
Amount available	$ 150
Expiration date	Feb. 28, 2016
Wells Fargo Bank, National Association [Member]
Lines of credit
Amount available	$ 150
Expiration date	Feb. 28, 2016