Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details)

v3.2.0.727
Fair Value Measurements (Details) - USD ($)
$ in Millions
May. 31, 2015
May. 31, 2014
Available-for-sale securities:    
Available-for-sale securities $ 3,595.6 $ 3,391.4
Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 103.1 65.8
Available-for-sale securities:    
Available-for-sale securities 3,595.6 3,391.4
Other 14.2 12.3
Liabilities:    
Other long-term liabilities 14.2 12.3
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 15.0 6.0
General obligation municipal bonds [Member]    
Available-for-sale securities:    
Available-for-sale securities 1,703.7 1,628.5
General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 55.1 10.9
Available-for-sale securities:    
Available-for-sale securities 1,703.7 1,628.5
Pre-refunded municipal bonds [Member]    
Available-for-sale securities:    
Available-for-sale securities [1] 102.7 142.8
Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 20.5 31.2
Available-for-sale securities:    
Available-for-sale securities 102.7 142.8
Revenue municipal bonds [Member]    
Available-for-sale securities:    
Available-for-sale securities 963.6 867.8
Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 12.3 17.7
Available-for-sale securities:    
Available-for-sale securities 963.6 867.8
Money market securities [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.2  
Variable Rate Demand Obligation [Member]    
Available-for-sale securities:    
Available-for-sale securities 825.6 752.3
Variable Rate Demand Obligation [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 825.6 752.3
Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.2 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Other 14.2 12.3
Liabilities:    
Other long-term liabilities 14.2 12.3
Quoted prices in active markets (Level 1) [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Quoted prices in active markets (Level 1) [Member] | General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Quoted prices in active markets (Level 1) [Member] | Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Quoted prices in active markets (Level 1) [Member] | Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Quoted prices in active markets (Level 1) [Member] | Money market securities [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.2  
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 0.0
Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 102.9 65.8
Available-for-sale securities:    
Available-for-sale securities 3,595.6 3,391.4
Other 0.0 0.0
Liabilities:    
Other long-term liabilities 0.0 0.0
Significant other observable Inputs (Level 2) [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 15.0 6.0
Significant other observable Inputs (Level 2) [Member] | General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 55.1 10.9
Available-for-sale securities:    
Available-for-sale securities 1,703.7 1,628.5
Significant other observable Inputs (Level 2) [Member] | Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 20.5 31.2
Available-for-sale securities:    
Available-for-sale securities 102.7 142.8
Significant other observable Inputs (Level 2) [Member] | Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 12.3 17.7
Available-for-sale securities:    
Available-for-sale securities 963.6 867.8
Significant other observable Inputs (Level 2) [Member] | Money market securities [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 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 825.6 752.3
Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Other 0.0 0.0
Liabilities:    
Other long-term liabilities 0.0 0.0
Significant unobservable Inputs (Level 3) [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Significant unobservable Inputs (Level 3) [Member] | General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Significant unobservable Inputs (Level 3) [Member] | Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Significant unobservable Inputs (Level 3) [Member] | Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Significant unobservable Inputs (Level 3) [Member] | Money market securities [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 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 $ 0.0
[1] (1) Pre-refunded municipal bonds are secured by an escrow fund of U.S. government obligations.