Quarterly report pursuant to Section 13 or 15(d)

Short-term Financing (Narrative) (Details)

v3.10.0.1
Short-term Financing (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Dec. 01, 2018
Nov. 30, 2018
Nov. 30, 2017
Nov. 30, 2018
Nov. 30, 2017
May 31, 2018
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]            
Line of Credit Facility [Line Items]            
Amounts outstanding   $ 0.0   $ 0.0   $ 0.0
Amount borrowed   $ 483.0 $ 700.0 $ 483.0 $ 700.0  
Number of days borrowed   4 days 6 days 10 days 19 days  
Weighted-average interest rate   5.12% 4.25% 5.06% 4.24%  
Weighted-average amount borrowed   $ 389.8 $ 445.8 $ 285.7 $ 331.6  
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Subsequent Event [Member]            
Line of Credit Facility [Line Items]            
Amount borrowed $ 400.0          
Due date Feb. 20, 2019          
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | LIBOR [Member] | Subsequent Event [Member]            
Line of Credit Facility [Line Items]            
Interest rate 3.50%          
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Three Days [Member]            
Line of Credit Facility [Line Items]            
Amount borrowed         $ 100.0  
Number of days borrowed         3 days  
Weighted-average interest rate         4.25%  
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]            
Line of Credit Facility [Line Items]            
Amounts outstanding   0.0   0.0   0.0
Amount borrowed   $ 135.5 $ 400.0 $ 223.0 $ 400.0  
Number of days borrowed   3 days 20 days 7 days 20 days  
Weighted-average interest rate   5.25% 2.84% 5.07% 2.84%  
Weighted-average amount borrowed   $ 83.0 $ 215.8 $ 111.8 $ 215.8  
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Subsequent Event [Member]            
Line of Credit Facility [Line Items]            
Amount borrowed $ 400.0          
Due date Feb. 20, 2019          
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | LIBOR [Member] | Subsequent Event [Member]            
Line of Credit Facility [Line Items]            
Interest rate 3.50%          
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Seven Days [Member]            
Line of Credit Facility [Line Items]            
Amount borrowed     $ 300.0   $ 300.0  
Number of days borrowed     7 days   7 days  
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Seven Days [Member] | LIBOR [Member]            
Line of Credit Facility [Line Items]            
Weighted-average interest rate     2.13%   2.13%  
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Eleven Days [Member]            
Line of Credit Facility [Line Items]            
Amount borrowed     $ 75.0   $ 75.0  
Number of days borrowed     11 days   11 days  
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Eleven Days [Member] | LIBOR [Member]            
Line of Credit Facility [Line Items]            
Weighted-average interest rate     2.19%   2.19%  
Revolving Credit Facility [Member] | PNC $150 Million Credit Facility [Member] | PNC Bank, National Association [Member]            
Line of Credit Facility [Line Items]            
Amounts outstanding   57.3   57.3   0.0
Amount borrowed   $ 57.7 $ 58.6 $ 57.7 $ 58.6  
Number of days borrowed   91 days 91 days 179 days 179 days  
Weighted-average interest rate   2.68% 1.78% 2.61% 1.73%  
Weighted-average amount borrowed   $ 57.3 $ 57.8 $ 56.6 $ 56.8  
Standby Letters of Credit [Member]            
Line of Credit Facility [Line Items]            
Maximum borrowing capacity   67.8   67.8   56.8
Amounts outstanding   $ 0.0 $ 0.0 $ 0.0 $ 0.0 $ 0.0
Minimum [Member] | Standby Letters of Credit [Member]            
Line of Credit Facility [Line Items]            
Expiration date       Apr. 01, 2019    
Maximum [Member] | Standby Letters of Credit [Member]            
Line of Credit Facility [Line Items]            
Expiration date       Jul. 01, 2020