Financial Instruments, Risk Management Activities, and Fair Values (Schedule of unallocated corporate items) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 25, 2014	May 26, 2013	May 27, 2012
Commodity Price Risk [Abstract]
Net gain (loss) on mark-to-market valuation of commodity positions	$ (4.9)	$ (7.6)	$ (122.5)
Net gain (loss) on commodity positions reclassified from unallocated corporate items to segment operating profit	51.2	13.7	35.7
Net mark-to-market revaluation of certain grain inventories	2.2	(1.7)	(17.4)
Net mark-to-market valuation of certain commodity positions recognized in unallocated corporate items	$ 48.5	$ 4.4	$ (104.2)