Financial Instruments, Risk Management Activities, and Fair Values (Schedule of unallocated corporate items) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 23, 2014	Nov. 24, 2013	Nov. 23, 2014	Nov. 24, 2013
Commodity Price Risk [Abstract]
Net loss on certain mark-to-market valuation of commodity positions	$ (40.2)	$ (3.7)	$ (81.6)	$ (16.0)
Net loss on commodity positions reclassified from unallocated corporate items to segment operating profit	32.8	18.7	28.0	34.5
Net mark-to-market revaluation of certain grain inventories	2.3	6.0	(0.7)	1.7
Net mark-to-market valuation of certain commodity positions recognized in unallocated corporate items	$ (5.1)	$ 21.0	$ (54.3)	$ 20.2