Quarterly report pursuant to Section 13 or 15(d)

Short-term Financing (Narrative) (Details)

v3.5.0.2
Short-term Financing (Narrative) (Details)
$ in Millions
 3 Months Ended
Aug. 31, 2016
USD ($)
loan
May 31, 2016
USD ($)
Line of Credit [Member]    
Line of Credit Facility [Line Items]    
Number of lines of credit | loan 4  
Amounts outstanding $ 0.0  
Line of Credit [Member] | PNC Bank, National Association [Member]    
Line of Credit Facility [Line Items]    
Expiration date Feb. 27, 2017  
Standby Letters of Credit [Member]    
Line of Credit Facility [Line Items]    
Maximum borrowing capacity $ 46.8 $ 43.0
Amounts outstanding 0.0  
Revolving Credit Facility [Member]    
Line of Credit Facility [Line Items]    
Amounts outstanding 0.0 0.0
Maximum borrowing capacity $ 1,000.0  
Expiration date Aug. 05, 2020  
Expiration term 5 years  
Revolving Credit Facility [Member] | PNC Bank, National Association [Member]    
Line of Credit Facility [Line Items]    
Amounts outstanding $ 51.3 $ 0.0
Maximum borrowing capacity $ 150.0  
Expiration date Mar. 17, 2019  
Expiration term 3 years  
Minimum [Member] | Standby Letters of Credit [Member]    
Line of Credit Facility [Line Items]    
Expiration date Dec. 01, 2016  
Maximum [Member] | Standby Letters of Credit [Member]    
Line of Credit Facility [Line Items]    
Expiration date Jul. 01, 2017