SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications from Accumulated Other Comprehensive Income (Loss) into Income (Details) - USD ($) $ in Millions	12 Months Ended
	May 30, 2021	May 31, 2020	May 26, 2019
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	$ (420.4)	$ (487.1)	$ (391.4)
Selling, general and administrative expenses	(1,403.0)	(1,622.5)	(1,473.4)
Equity method investment earnings	84.4	73.2	75.8
Income from continuing operations before income taxes and equity method investment earnings	1,410.3	969.9	823.3
Income tax expense	(193.8)	(201.3)	(218.8)
Net income attributable to Conagra Brands, Inc.	1,298.8	840.1	678.3
Pension and postretirement non-service income	(54.5)	(9.9)	(35.1)
Reclassification out of accumulated other comprehensive loss | Cash flow hedges
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	(3.2)	(3.3)	(1.9)
Selling, general and administrative expenses	(0.5)	0.0	0.0
Equity method investment earnings	2.1	0.0	0.0
Income from continuing operations before income taxes and equity method investment earnings	(1.6)	(3.3)	(1.9)
Income tax expense	1.0	0.9	0.5
Net income attributable to Conagra Brands, Inc.	(0.6)	(2.4)	(1.4)
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	0.2	0.6	0.9
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	(3.5)	(4.6)	(1.4)
Reclassification out of accumulated other comprehensive loss | Pension and Postretirement healthcare settlement | Pension Benefits
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pension and postretirement non-service income	0.0	(2.1)	0.0
Reclassification out of accumulated other comprehensive loss | Pension and Postretirement healthcare settlement | Postretirement Healthcare
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pension and postretirement non-service income	(0.5)	(0.2)	(1.0)
Reclassification out of accumulated other comprehensive loss | Curtailment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pension and postretirement non-service income	0.2	0.8	0.0
Reclassification out of accumulated other comprehensive loss | Amortization of pension and postretirement benefit obligations:
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income from continuing operations before income taxes and equity method investment earnings	(3.6)	(5.5)	(1.5)
Income tax expense	0.9	1.4	0.4
Net income attributable to Conagra Brands, Inc.	(2.7)	(4.1)	(1.1)
Reclassification out of accumulated other comprehensive loss | Currency translation losses
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Selling, general and administrative expenses	0.0	0.0	10.4
Income from continuing operations before income taxes and equity method investment earnings	0.0	0.0	10.4
Income tax expense	0.0	0.0	0.0
Net income attributable to Conagra Brands, Inc.	$ 0.0	$ 0.0	$ 10.4