Fair Value Measurements (Details) (USD $)
In Millions, unless otherwise specified |
Feb. 28, 2013
|
May 31, 2012
|
---|---|---|
Available-for-sale securities: | ||
Available-for-sale securities | $ 4,873.7 | $ 3,059.0 |
Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | 4,873.7 | 3,059.0 |
Other securities | 10.3 | 9.2 |
Liabilities: | ||
Other long-term liabilities | 10.3 | 9.2 |
General obligation municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | 1,380.2 | 1,333.9 |
Pre-refunded municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | 211.4 | 334.3 |
Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | 682.0 | 501.0 |
Variable rate demand notes [Member] | Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | 2,600.1 | 889.8 |
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 | 10.3 | 9.2 |
Liabilities: | ||
Other long-term liabilities | 10.3 | 9.2 |
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 |
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] | 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] | Variable rate demand notes [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 | 4,873.7 | 3,059.0 |
Other securities | 0 | 0 |
Liabilities: | ||
Other long-term liabilities | 0 | 0 |
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 | 1,380.2 | 1,333.9 |
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 | 211.4 | 334.3 |
Significant other observable Inputs (Level 2) [Member] | Revenue municipal bonds [Member] | Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | 682.0 | 501.0 |
Significant other observable Inputs (Level 2) [Member] | Variable rate demand notes [Member] | Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | 2,600.1 | 889.8 |
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] | General obligation 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] | 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] | Variable rate demand notes [Member] | Fair Value, Measurements, Recurring [Member]
|
||
Available-for-sale securities: | ||
Available-for-sale securities | $ 0 | $ 0 |