Risk Management Activities (Schedule of unallocated corporate items) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2021	Feb. 23, 2020	Feb. 28, 2021	Feb. 23, 2020
Commodity Price Risk [Abstract]
Net gain (loss) on mark-to-market valuation of certain commodity positions	$ 51.0	$ (8.7)	$ 95.0	$ (19.7)
Net loss (gain) on commodity positions reclassified from unallocated corporate items to segment operating profit	(3.9)	4.5	12.8	19.8
Net mark-to-market revaluation of certain grain inventories	8.6	(4.4)	10.2	(1.1)
Net mark-to-market valuation of certain commodity positions recognized in unallocated corporate items	$ 55.7	$ (8.6)	$ 118.0	$ (1.0)