SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications From Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 26, 2017	Feb. 28, 2016	Feb. 26, 2017	Feb. 28, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense, net	$ (45.7)	$ (76.4)	$ (158.0)	$ (235.7)
Selling, general and administrative expenses	349.7	447.0	999.3	1,293.0
Income (loss) from discontinued operations, net of tax	0.7	134.9	103.7	(1,031.9)
Equity method investment earnings	21.8	8.6	52.1	50.7
Income tax expense	(67.9)	(33.6)	(315.5)	(126.0)
Net income (loss) attributable to Conagra Brands, Inc.	179.7	204.6	488.0	(794.6)
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	(0.2)	(2.1)	(0.2)	(2.1)
Total before tax	(0.2)	(2.1)	(0.2)	(2.1)
Income tax expense	0.1	0.8	0.1	0.8
Net income (loss) attributable to Conagra Brands, Inc.	(0.1)	(1.3)	(0.1)	(1.3)
Reclassification out of accumulated other comprehensive loss | Pension and postretirement liabilities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total before tax	13.0	(10.9)	11.2	(13.5)
Income tax expense	(5.0)	3.4	(4.3)	4.4
Net income (loss) attributable to Conagra Brands, Inc.	8.0	(7.5)	6.9	(9.1)
Reclassification out of accumulated other comprehensive loss | Net prior service benefit
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Selling, general and administrative expenses	(0.9)	(1.2)	(2.9)	(3.8)
Reclassification out of accumulated other comprehensive loss | 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	(4.3)
Reclassification out of accumulated other comprehensive loss | Pension settlement of equity method investment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Equity method investment earnings	0.0	(5.4)	0.0	(5.4)
Reclassification out of accumulated other comprehensive loss | Pension settlement
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Selling, general and administrative expenses	13.8	0.0	13.8	0.0
Reclassification out of accumulated other comprehensive loss | Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Selling, general and administrative expenses	0.1	0.0	0.3	0.0
Reclassification out of accumulated other comprehensive loss | 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	73.4
Total before tax	0.0	73.4	0.0	73.4
Income tax expense	0.0	0.0	0.0	0.0
Net income (loss) attributable to Conagra Brands, Inc.	$ 0.0	$ 73.4	$ 0.0	$ 73.4