Financial Instruments, Risk Management Activities, and Fair Values (Schedule of unallocated corporate items) (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2020	May 26, 2019	May 27, 2018
Commodity Price Risk [Abstract]
Net gain (loss) on mark-to-market valuation of commodity positions	$ (63.0)	$ (39.0)	$ 14.3
Net loss (gain) on commodity positions reclassified from unallocated corporate items to segment operating profit	35.6	10.0	11.3
Net mark-to-market revaluation of certain grain inventories	2.7	(7.0)	6.5
Net mark-to-market valuation of certain commodity positions recognized in unallocated corporate items	$ (24.7)	$ (36.0)	$ 32.1