Financial Instruments, Risk Management Activities, and Fair Values (Schedule of maturities of available for sale securities) (Details) $ in Millions	May 31, 2020 USD ($)
Schedule of Available-for-Sale Securities [Line Items]
Cost	$ 57.0
Fair Value	61.6
Debt Securities [Member] | Available-for-Sale Securities Debt Maturities Within One Year [Member]
Schedule of Available-for-Sale Securities [Line Items]
Cost	56.7
Fair Value	56.7
Equity Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Cost	0.3
Fair Value	$ 4.9