SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Reclassifications From Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 26, 2018	Aug. 27, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and postretirement non-service income	$ 257.3	$ 259.6
Income from continuing operations before income taxes and equity method investment earnings	219.4	243.6
Income tax expense	(57.4)	(120.0)
Net income attributable to Conagra Brands, Inc.	178.2	152.5
Reclassified to Pension and postretirement non-service income	(10.2)	(20.6)
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	0.2	(0.1)
Income from continuing operations before income taxes and equity method investment earnings	(0.2)	(0.1)
Income tax expense	0.1	0.0
Net income attributable to Conagra Brands, Inc.	(0.1)	(0.1)
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	(0.4)	$ 0.0
Accounting Standards Update 2017-07
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and postretirement non-service income	(20.6)
Reclassified to Pension and postretirement non-service income	$ 20.6