Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Details)

v3.3.0.814
Fair Value Measurements (Details) - USD ($)
$ in Millions
Aug. 31, 2015
May. 31, 2015
Available-for-sale securities:    
Available-for-sale securities $ 2,902.3 $ 3,595.6
Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 220.1 103.1
Available-for-sale securities:    
Available-for-sale securities 2,902.3 3,595.6
Other 14.7 14.2
Liabilities:    
Other long-term liabilities 14.7 14.2
Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.1 0.2
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Other 14.7 14.2
Liabilities:    
Other long-term liabilities 14.7 14.2
Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 220.0 102.9
Available-for-sale securities:    
Available-for-sale securities 2,902.3 3,595.6
Other 0.0 0.0
Liabilities:    
Other long-term liabilities 0.0 0.0
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
Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 198.0 15.0
Commercial paper [Member] | Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Commercial paper [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 198.0 15.0
Commercial paper [Member] | Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
General obligation municipal bonds [Member]    
Available-for-sale securities:    
Available-for-sale securities 1,723.5 1,703.7
General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 22.0 55.1
Available-for-sale securities:    
Available-for-sale securities 1,723.5 1,703.7
General obligation municipal bonds [Member] | Quoted prices in active markets (Level 1) [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
General obligation municipal bonds [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 22.0 55.1
Available-for-sale securities:    
Available-for-sale securities 1,723.5 1,703.7
General obligation municipal bonds [Member] | 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
Money market securities [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.1 0.2
Money market securities [Member] | Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.1 0.2
Money market securities [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Money market securities [Member] | Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents 0.0 0.0
Corporate bond securities [Member]    
Available-for-sale securities:    
Available-for-sale securities 64.8  
Corporate bond securities [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 64.8  
Corporate bond securities [Member] | Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 0.0  
Corporate bond securities [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 64.8  
Corporate bond securities [Member] | Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 0.0  
Pre-refunded municipal bonds [Member]    
Available-for-sale securities:    
Available-for-sale securities 96.3 102.7
Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   20.5
Available-for-sale securities:    
Available-for-sale securities 96.3 102.7
Pre-refunded municipal bonds [Member] | Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Pre-refunded municipal bonds [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   20.5
Available-for-sale securities:    
Available-for-sale securities 96.3 102.7
Pre-refunded municipal bonds [Member] | Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Revenue municipal bonds [Member]    
Available-for-sale securities:    
Available-for-sale securities 957.6 963.6
Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   12.3
Available-for-sale securities:    
Available-for-sale securities 957.6 963.6
Revenue municipal bonds [Member] | Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Revenue municipal bonds [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   12.3
Available-for-sale securities:    
Available-for-sale securities 957.6 963.6
Revenue municipal bonds [Member] | Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Assets:    
Cash Equivalents   0.0
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
US government agencies debt securities [Member]    
Available-for-sale securities:    
Available-for-sale securities 37.1  
US government agencies debt securities [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 37.1  
US government agencies debt securities [Member] | Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 0.0  
US government agencies debt securities [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 37.1  
US government agencies debt securities [Member] | Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 0.0  
Variable rate demand notes [Member]    
Available-for-sale securities:    
Available-for-sale securities 23.0 825.6
Variable rate demand notes [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 23.0 825.6
Variable rate demand notes [Member] | Quoted prices in active markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 0.0 0.0
Variable rate demand notes [Member] | Significant other observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities 23.0 825.6
Variable rate demand notes [Member] | Significant unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Available-for-sale securities:    
Available-for-sale securities $ 0.0 $ 0.0