Risk Management Activities (Schedule of unallocated corporate items) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2016	Feb. 22, 2015	Feb. 28, 2016	Feb. 22, 2015
Commodity Price Risk [Abstract]
Net loss on mark-to-market valuation of certain commodity positions	$ (42.7)	$ (64.8)	$ (96.7)	$ (146.4)
Net loss on commodity positions reclassified from unallocated corporate items to segment operating profit	39.8	28.6	101.9	56.6
Net mark-to-market revaluation of certain grain inventories	(4.4)	(7.5)	(2.1)	(8.2)
Net mark-to-market valuation of certain commodity positions recognized in unallocated corporate items	$ (7.3)	$ (43.7)	$ 3.1	$ (98.0)