Quarterly report pursuant to Section 13 or 15(d)

Short-term Financing (Lines of Credit Facility Amount Borrowed) (Details)

v3.7.0.1
Short-term Financing (Lines of Credit Facility Amount Borrowed) (Details) - Revolving Credit Facility [Member] - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Feb. 28, 2017
Feb. 28, 2017
Feb. 29, 2016
JP Morgan Chase Bank, NA [Member]      
Line of Credit Facility [Line Items]      
Number of days borrowed 8 days 27 days 3 days
Maximum amount borrowed $ 250.0 $ 350.0 $ 350.0
Weighted-average amount borrowed $ 81.3 $ 183.3 $ 217.0
Weighted-average interest rate 2.24% 2.68% 3.25%
PNC Bank, National Association [Member]      
Line of Credit Facility [Line Items]      
Number of days borrowed 90 days 267 days  
Maximum amount borrowed $ 55.6 $ 55.6  
Weighted-average amount borrowed $ 55.3 $ 52.6  
Weighted-average interest rate 1.27% 1.13%