SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications from Accumulated Other Comprehensive Income (Loss) into Income (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 29, 2021	Aug. 30, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	$ (94.2)	$ (113.7)
Pension and postretirement non-service income	(16.1)	(13.8)
Equity method investment earnings	20.2	6.5
Income before income taxes and equity method investment earnings	285.2	410.0
Income tax expense	(69.7)	(86.7)
Net income attributable to Conagra Brands, Inc.	235.4	329.0
Reclassification out of accumulated other comprehensive loss | Cash flow hedges
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	(0.8)	(0.9)
Equity method investment earnings	0.5	0.0
Income before income taxes and equity method investment earnings	(0.3)	(0.9)
Income tax expense	0.1	0.2
Net income attributable to Conagra Brands, Inc.	(0.2)	(0.7)
Reclassification out of accumulated other comprehensive loss | Net prior service cost
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pension and postretirement non-service income	0.0	0.1
Reclassification out of accumulated other comprehensive loss | Net actuarial gain
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pension and postretirement non-service income	(0.8)	(0.9)
Reclassification out of accumulated other comprehensive loss | Pension and postretirement liabilities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes and equity method investment earnings	(0.8)	(0.8)
Income tax expense	0.2	0.2
Net income attributable to Conagra Brands, Inc.	$ (0.6)	$ (0.6)