Financial Instruments, Risk Management Activities, and Fair Values (Schedule of interest rate derivatives) (Details) (Interest Rate Swap Pay Floating [Member], USD $) In Millions, unless otherwise specified	Feb. 24, 2013	May 27, 2012
Interest Rate Swap Pay Floating [Member]
Derivative [Line Items]
Derivative Notional Amount	$ 550.0	$ 834.6
Pay Floating Average receive rate	1.10%	1.70%
Pay Floating Average pay rate	0.40%	0.30%