Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
Short-term Financing (Credit Facility Amount Borrowed) (Details) - Revolving Credit Facility [Member] - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Nov. 30, 2017
Nov. 30, 2016
Nov. 30, 2017
Nov. 30, 2016
JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]        
Line of Credit Facility [Line Items]        
Number of days borrowed 6 days 15 days 19 days 19 days
Maximum amount borrowed $ 700.0 $ 350.0 $ 700.0 $ 350.0
Weighted-average amount borrowed $ 445.8 $ 223.3 $ 331.6 $ 226.3
Weighted-average interest rate 4.25% 2.53% 4.24% 2.74%
JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]        
Line of Credit Facility [Line Items]        
Number of days borrowed 20 days   20 days  
Maximum amount borrowed $ 400.0   $ 400.0  
Weighted-average amount borrowed $ 215.8   $ 215.8  
Weighted-average interest rate 2.84%   2.84%  
PNC $150 Million Credit Facility [Member] | PNC Bank, National Association [Member]        
Line of Credit Facility [Line Items]        
Number of days borrowed 91 days 91 days 179 days 177 days
Maximum amount borrowed $ 58.6 $ 53.1 $ 58.6 $ 53.1
Weighted-average amount borrowed $ 57.8 $ 52.2 $ 56.8 $ 51.8
Weighted-average interest rate 1.78% 1.08% 1.73% 1.05%