Financial Instruments, Risk Management Activities, and Fair Values (Schedule of interest rate swaps and maturities) (Details) (Interest Rate Contracts [Member], USD $) In Millions, unless otherwise specified	Nov. 23, 2014	May 25, 2014
Interest Rate Contracts [Member]
Derivative [Line Items]
Derivative, notional amount	$ 1,250.0	$ 250.0
Average receive rate	1.60%	0.90%
Average pay rate	0.60%	0.50%
Swap Contract Maturities, Year One	250.0
Swap Contract Maturities, Year Two	0
Swap Contract Maturities, Year Three	500.0
Swap Contract Maturities, Year Four	0
Swap Contract Maturities, Year Five	500.0
Swap Contract Maturities, Total	$ 1,250.0