Financial Instruments, Risk Management Activities, and Fair Values (Schedule of offsetting assets and liabilities) (Details) (USD $) In Millions, unless otherwise specified	Aug. 25, 2013	May 26, 2013
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	$ 83.4	$ 65.8
Gross Liabilities Offset in the Balance Sheet	0	(19.6)
Net Amounts of Assets	83.4	46.2
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	(28.5)	(1.7)
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	54.9	44.5
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	(31.6)	(25.2)
Gross Assets Offset in the Balance Sheet	0	19.6
Net Amounts of Liabilities	(31.6)	(5.6)
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	28.5	1.7
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	(3.1)	(3.9)
Commodity Contract [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	42.4	33.0
Gross Liabilities Offset in the Balance Sheet	0	(19.6)
Net Amounts of Assets	42.4	13.4
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	(22.2)	0
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	20.2	13.4
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	(24.2)	(23.5)
Gross Assets Offset in the Balance Sheet	0	19.6
Net Amounts of Liabilities	(24.2)	(3.9)
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	22.2	0
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	(2.0)	(3.9)
Interest Rate Contract [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	23.7	10.3
Gross Liabilities Offset in the Balance Sheet	0	0
Net Amounts of Assets	23.7	10.3
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	(0.5)	0
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	23.2	10.3
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	(0.8)	0
Gross Assets Offset in the Balance Sheet	0	0
Net Amounts of Liabilities	(0.8)	0
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	0.5	0
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	(0.3)	0
Foreign Exchange Contract [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	17.3	22.5
Gross Liabilities Offset in the Balance Sheet	0	0
Net Amounts of Assets	17.3	22.5
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	(5.8)	(1.7)
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	11.5	20.8
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	(6.6)	(1.7)
Gross Assets Offset in the Balance Sheet	0	0
Net Amounts of Liabilities	(6.6)	(1.7)
Financial Instruments, Gross Amounts Not Offset in the Balance Sheet	5.8	1.7
Cash Collateral Received, Gross Amounts Not Offset in the Balance Sheet	0	0
Net Amount	$ (0.8)	$ 0