Quarterly report pursuant to Section 13 or 15(d)

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

v3.6.0.2
Short-term Financing (Lines of Credit Facility Amount Borrowed) (Details) - Revolving Credit Facility [Member] - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Nov. 30, 2016
Nov. 30, 2015
Nov. 30, 2016
Nov. 30, 2015
Line of Credit Facility [Line Items]        
Number of days borrowed 15 days 2 days 19 days 3 days
Maximum amount borrowed $ 350.0 $ 350.0 $ 350.0 $ 350.0
Weighted-average amount borrowed $ 223.3 $ 225.0 $ 226.3 $ 217.0
Weighted-average interest rate 2.53% 3.25% 2.74% 3.25%
PNC Bank, National Association [Member]        
Line of Credit Facility [Line Items]        
Number of days borrowed 91 days   177 days  
Maximum amount borrowed $ 53.1   $ 53.1  
Weighted-average amount borrowed $ 52.2   $ 51.8  
Weighted-average interest rate 1.08%   1.05%