SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications from Accumulated Other Comprehensive Loss into Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	May 27, 2018	Feb. 25, 2018	Nov. 26, 2017	Aug. 27, 2017	May 28, 2017	Feb. 26, 2017	Nov. 27, 2016	Aug. 28, 2016	May 27, 2018	May 28, 2017	May 29, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense, net									$ (158.7)	$ (195.5)	$ (295.8)
Selling, general and administrative expenses									1,318.0	1,417.1	2,024.6
Income (loss) from discontinued operations, net of tax	$ (0.3)	$ 14.5	$ 0.4	$ (0.3)	$ (1.7)	$ 0.7	$ 11.6	$ 91.4	14.3	102.0	(794.4)
Equity method investment earnings									97.3	71.2	66.1
Total before tax									972.1	800.7	174.9
Income tax expense									(174.6)	(254.7)	(46.4)
Net income (loss) attributable to Conagra Brands, Inc.	$ 69.6	$ 362.8	$ 223.5	$ 152.5	$ 151.3	$ 179.7	$ 122.1	$ 186.2	808.4	639.3	(677.0)
Reclassification out of Accumulated Other Comprehensive Income | Cash flow hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense, net									0.1	(0.2)	(2.1)
Total before tax									0.1	(0.2)	(2.1)
Income tax expense									0.0	0.1	0.8
Net income (loss) attributable to Conagra Brands, Inc.									0.1	(0.1)	(1.3)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of pension and postretirement healthcare liabilities:
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total before tax									0.9	10.4	(14.5)
Income tax expense									(0.2)	(4.0)	4.9
Net income (loss) attributable to Conagra Brands, Inc.									0.7	6.4	(9.6)
Reclassification out of Accumulated Other Comprehensive Income | Net prior service benefit
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Selling, general and administrative expenses									(0.4)	(3.9)	(5.1)
Reclassification out of Accumulated Other Comprehensive Income | Divestiture of Private Brands
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income (loss) from discontinued operations, net of tax									0.0	0.0	(4.3)
Reclassification out of Accumulated Other Comprehensive Income | Pension settlement of equity method investee
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Equity method investment earnings									0.0	0.0	(5.2)
Reclassification out of Accumulated Other Comprehensive Income | Pension settlement
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Selling, general and administrative expenses									1.3	13.8	0.0
Reclassification out of Accumulated Other Comprehensive Income | Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Selling, general and administrative expenses									0.0	0.5	0.1
Reclassification out of Accumulated Other Comprehensive Income | Currency translation losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income (loss) from discontinued operations, net of tax									0.0	0.0	73.4
Total before tax									0.0	0.0	73.4
Income tax expense									0.0	0.0	0.0
Net income (loss) attributable to Conagra Brands, Inc.									$ 0.0	$ 0.0	$ 73.4