Risk Management Activities (Schedule of unallocated corporate items) (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 30, 2015	Aug. 24, 2014
Commodity Price Risk [Abstract]
Net gain (loss) on certain mark-to-market valuation of commodity positions	$ (22.3)	$ (41.4)
Net loss on commodity positions reclassified from unallocated corporate items to segment operating profit	26.9	(4.8)
Net mark-to-market revaluation of certain grain inventories	(1.9)	(3.0)
Net mark-to-market valuation of certain commodity positions recognized in unallocated corporate items	$ 2.7	$ (49.2)