Financial Instruments, Risk Management Activities, and Fair Values (Schedule of maturities of available for sale securities) (Details) - USD ($) $ in Millions	May 29, 2016	May 31, 2015
Schedule of Available-for-Sale Securities [Line Items]
Cost	$ 167.5	$ 4.4
Fair Value	174.2	10.9
Debt Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Cost	165.7	2.6
Fair Value	165.8	2.6
Debt Securities [Member] | Available-for-Sale Securities Debt Maturities Within One Year [Member]
Schedule of Available-for-Sale Securities [Line Items]
Cost	165.7
Fair Value	165.8
Equity Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Cost	1.8	1.8
Fair Value	$ 8.4	$ 8.3