SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications from Accumulated Other Comprehensive Loss into Income (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Feb. 28, 2021	Nov. 29, 2020	Aug. 30, 2020	Feb. 23, 2020	Nov. 24, 2019	Aug. 25, 2019	Feb. 28, 2021	Feb. 23, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	$ (100.6)			$ (117.7)			$ (322.0)	$ (361.8)
Pension and postretirement non-service income	(13.7)			(16.4)			(41.2)	(37.2)
Selling, general and administrative expenses	(309.7)			(319.9)			(967.7)	(1,090.5)
Income before income taxes and equity method investment earnings	361.8			263.2			1,209.0	731.7
Income tax expense	(101.6)			(68.9)			(269.0)	(141.5)
Net income attributable to Conagra Brands, Inc.	281.4	$ 378.9	$ 329.0	204.4	$ 260.5	$ 173.8	989.3	638.7
Reclassification out of accumulated other comprehensive loss | Derivative adjustments, net of reclassification adjustments
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	(0.8)			(0.9)			(2.4)	(2.5)
Selling, general and administrative expenses							(0.5)	0.0
Income before income taxes and equity method investment earnings	(0.8)			(0.9)			(2.9)	(2.5)
Income tax expense	0.2			0.2			0.7	0.6
Net income attributable to Conagra Brands, Inc.	(0.6)			(0.7)			(2.2)	(1.9)
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			0.2			0.2	0.5
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)			(1.1)			(2.6)	(3.4)
Reclassification out of accumulated other comprehensive loss | Curtailment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pension and postretirement non-service income	0.0			0.2			0.0	0.8
Reclassification out of accumulated other comprehensive loss | Settlement
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pension and postretirement non-service income	0.0			(2.1)			0.0	(2.1)
Reclassification out of accumulated other comprehensive loss | Pension and postretirement benefit obligations, net of reclassification adjustments
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes and equity method investment earnings	(0.8)			(2.8)			(2.4)	(4.2)
Income tax expense	0.2			0.6			0.6	1.0
Net income attributable to Conagra Brands, Inc.	$ (0.6)			$ (2.2)			$ (1.8)	$ (3.2)