Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details)

v3.21.2
Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($)
$ in Millions
Aug. 31, 2021
May 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Restricted and unrestricted cash equivalents $ 11.8 $ 2.9
Available-for-sale securities 3,002.4 3,020.2
Other 36.9 34.0
Other long-term liabilities 35.3 32.6
Asset-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 81.1 87.9
Corporate Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 674.1 664.4
Municipal Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 1,703.0 1,699.7
U.S. Government Agency And Treasury Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 544.2 568.2
Money Market Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Restricted and unrestricted cash equivalents 11.8 2.9
Quoted Prices in Active Markets (Level 1) [Member] | Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Restricted and unrestricted cash equivalents 11.8 2.9
Other 36.9 34.0
Other long-term liabilities 35.3 32.6
Quoted Prices in Active Markets (Level 1) [Member] | Money Market Securities [Member] | Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Restricted and unrestricted cash equivalents 11.8 2.9
Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 3,002.4 3,020.2
Significant Other Observable Inputs (Level 2) [Member] | Asset-Backed Securities [Member] | Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 81.1 87.9
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member] | Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 674.1 664.4
Significant Other Observable Inputs (Level 2) [Member] | Municipal Bonds [Member] | Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 1,703.0 1,699.7
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agency And Treasury Securities [Member] | Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities $ 544.2 $ 568.2