SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications From Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 30, 2020	Aug. 25, 2019
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Interest expense, net	$ (113.7)	$ (122.7)
Pension and postretirement non-service income	(13.8)	(9.5)
Income before income taxes and equity method investment earnings	410.0	150.5
Income tax expense	(86.7)	11.5
Net income attributable to Conagra Brands, Inc.	329.0	173.8
Reclassification out of accumulated other comprehensive loss | Derivative adjustments, net of reclassification adjustments
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Interest expense, net	(0.9)	(0.8)
Income before income taxes and equity method investment earnings	(0.9)	(0.8)
Income tax expense	0.2	0.2
Net income attributable to Conagra Brands, Inc.	(0.7)	(0.6)
Reclassification out of accumulated other comprehensive loss | Net prior service cost
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Pension and postretirement non-service income	0.1	0.2
Reclassification out of accumulated other comprehensive loss | Net actuarial gain
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Pension and postretirement non-service income	(0.9)	(1.2)
Reclassification out of accumulated other comprehensive loss | Pension and postretirement liabilities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Income before income taxes and equity method investment earnings	(0.8)	(0.4)
Income tax expense	0.2	0.1
Net income attributable to Conagra Brands, Inc.	(0.6)	(0.3)
Reclassification out of accumulated other comprehensive loss | Curtailment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Pension and postretirement non-service income	$ 0.0	$ 0.6