Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details)

v2.4.0.8
Fair Value Measurements (Details) (USD $)
In Millions, unless otherwise specified
May 31, 2013
May 31, 2012
Available-for-sale securities:    
Available-for-sale securities $ 3,691.4 $ 3,059.0
Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 3,691.4 3,059.0
Other securities 10.7 9.2
Liabilities:    
Other long-term liabilities 10.7 9.2
Variable Rate Demand Obligation [Member]
   
Available-for-sale securities:    
Available-for-sale securities 1,276.7 889.8
Variable Rate Demand Obligation [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 1,276.7 889.8
Revenue municipal bonds [Member]
   
Available-for-sale securities:    
Available-for-sale securities 754.0 501.0
Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 754.0 501.0
Pre-refunded municipal bonds [Member]
   
Available-for-sale securities:    
Available-for-sale securities 203.9 [1] 334.3 [1]
Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 203.9 334.3
General obligation municipal bonds [Member]
   
Available-for-sale securities:    
Available-for-sale securities 1,456.8 1,333.9
General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 1,456.8 1,333.9
Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Other securities 10.7 9.2
Liabilities:    
Other long-term liabilities 10.7 9.2
Quoted prices in active markets (Level 1) [Member] | Variable Rate Demand Obligation [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Quoted prices in active markets (Level 1) [Member] | Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Quoted prices in active markets (Level 1) [Member] | Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Quoted prices in active markets (Level 1) [Member] | General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 3,691.4 3,059.0
Other securities 0 0
Liabilities:    
Other long-term liabilities 0 0
Significant other observable Inputs (Level 2) [Member] | Variable Rate Demand Obligation [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 1,276.7 889.8
Significant other observable Inputs (Level 2) [Member] | Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 754.0 501.0
Significant other observable Inputs (Level 2) [Member] | Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 203.9 334.3
Significant other observable Inputs (Level 2) [Member] | General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 1,456.8 1,333.9
Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Other securities 0 0
Liabilities:    
Other long-term liabilities 0 0
Significant unobservable Inputs (Level 3) [Member] | Variable Rate Demand Obligation [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Significant unobservable Inputs (Level 3) [Member] | Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Significant unobservable Inputs (Level 3) [Member] | Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities 0 0
Significant unobservable Inputs (Level 3) [Member] | General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
   
Available-for-sale securities:    
Available-for-sale securities $ 0 $ 0
[1] (1) Pre-refunded municipal bonds are secured by an escrow fund of U.S. government obligations.