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 28, 2017	Feb. 26, 2017	Nov. 27, 2016	Aug. 28, 2016	May 29, 2016	Feb. 28, 2016	Nov. 29, 2015	Aug. 30, 2015	May 28, 2017	May 29, 2016	May 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense, net									$ (195.5)	$ (295.8)	$ (328.2)
Selling, general and administrative expenses									1,417.1	2,024.6	1,383.4
Income (loss) from discontinued operations, net of tax	$ (1.7)	$ 0.7	$ 11.6	$ 91.4	$ 237.5	$ 134.9	$ 79.2	$ (1,246.0)	102.0	(794.4)	(692.1)
Equity method investment earnings									71.2	66.1	79.4
Cost of goods sold									5,484.8	6,234.9	6,737.8
Total before tax									800.7	174.9	664.0
Income tax expense									(254.7)	(46.4)	(212.7)
Net income (loss) attributable to Conagra Brands, Inc.	$ 151.3	$ 179.7	$ 122.1	$ 186.2	$ 117.6	$ 204.6	$ 154.9	$ (1,154.1)	639.3	(677.0)	(252.6)
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									(0.2)	(2.1)	(0.5)
Total before tax									(0.2)	(2.1)	(0.5)
Income tax expense									0.1	0.8	0.2
Net income (loss) attributable to Conagra Brands, Inc.									(0.1)	(1.3)	(0.3)
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									10.4	(14.5)	0.8
Income tax expense									(4.0)	4.9	(0.3)
Net income (loss) attributable to Conagra Brands, Inc.									6.4	(9.6)	0.5
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									(3.9)	(5.1)	(4.2)
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	(4.3)	0.0
Reclassification out of Accumulated Other Comprehensive Income | Pension settlement of equity method investment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Equity method investment earnings									0.0	(5.2)	0.0
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									13.8	0.0	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									0.5	0.1	3.5
Reclassification out of Accumulated Other Comprehensive Income | Curtailment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold									0.0	0.0	1.5
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	73.4	0.0
Total before tax									0.0	73.4	0.0
Income tax expense									0.0	0.0	0.0
Net income (loss) attributable to Conagra Brands, Inc.									$ 0.0	$ 73.4	$ 0.0