SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications From Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2020	Feb. 23, 2020	Nov. 24, 2019	Aug. 25, 2019	May 26, 2019	Feb. 24, 2019	Nov. 25, 2018	Aug. 26, 2018	May 31, 2020	May 26, 2019	May 27, 2018
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Interest expense, net									$ (487.1)	$ (391.4)	$ (158.7)
Pension and postretirement non-service income									(9.9)	(35.1)	(80.4)
Selling, general and administrative expenses									1,622.5	1,473.4	1,398.4
Income from continuing operations before income taxes and equity method investment earnings									969.9	823.3	874.8
Income tax expense									(201.3)	(218.8)	(174.6)
Net income attributable to Conagra Brands, Inc.	$ 201.4	$ 204.4	$ 260.5	$ 173.8	$ 126.5	$ 242.0	$ 131.6	$ 178.2	840.1	678.3	808.4
Reclassification out of accumulated other comprehensive loss | Cash flow hedges
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Interest expense, net									(3.3)	(1.9)	0.1
Income from continuing operations before income taxes and equity method investment earnings									(3.3)	(1.9)	0.1
Income tax expense									0.9	0.5	0.0
Net income attributable to Conagra Brands, Inc.									(2.4)	(1.4)	0.1
Reclassification out of accumulated other comprehensive loss | Net prior service cost (benefit)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Pension and postretirement non-service income									0.6	0.9	(0.4)
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									(4.6)	(1.4)	0.0
Reclassification out of accumulated other comprehensive loss | Pension and Postretirement healthcare settlement | Pension Benefits
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Pension and postretirement non-service income									(2.1)	0.0	1.3
Reclassification out of accumulated other comprehensive loss | Pension and Postretirement healthcare settlement | Postretirement Healthcare
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Pension and postretirement non-service income									(0.2)	(1.0)	0.0
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									0.8	0.0	0.0
Reclassification out of accumulated other comprehensive loss | Amortization of pension and postretirement benefit obligations:
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Income from continuing operations before income taxes and equity method investment earnings									(5.5)	(1.5)	0.9
Income tax expense									1.4	0.4	(0.2)
Net income attributable to Conagra Brands, Inc.									(4.1)	(1.1)	0.7
Reclassification out of accumulated other comprehensive loss | Currency translation losses
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Selling, general and administrative expenses									0.0	10.4	0.0
Income from continuing operations before income taxes and equity method investment earnings									0.0	10.4	0.0
Income tax expense									0.0	0.0	0.0
Net income attributable to Conagra Brands, Inc.									$ 0.0	$ 10.4	$ 0.0