STOCKHOLDERS' EQUITY - Reconciliation of Stockholders' Equity Accounts (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Feb. 28, 2021	Nov. 29, 2020	Aug. 30, 2020	Feb. 23, 2020	Nov. 24, 2019	Aug. 25, 2019	Feb. 28, 2021	Feb. 23, 2020
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period	$ 8,469.5	$ 8,199.0	$ 7,950.7	$ 7,690.6	$ 7,516.8	$ 7,463.7	$ 7,950.7	$ 7,463.7
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Stock option and incentive plans	10.2	15.4	$ 7.4	13.3	13.5	7.0
Currency translation adjustments	0.1	10.7	17.5	3.8	3.5	(11.6)
Repurchase of common shares	(298.1)
Derivative adjustments	(0.1)	(0.1)	(1.2)	(0.9)	(1.4)	(1.8)
Activities of noncontrolling interests	0.3	0.6	0.8	0.3	1.8	0.5
Pension and postretirement healthcare benefits	(0.6)	(0.6)	(0.3)	56.0	(0.7)	(11.4)
Dividends declared on common stock; $0.2125 per share	(132.9)	(134.4)	(103.8)	(103.6)	(103.4)	(103.4)
Net income attributable to Conagra Brands, Inc.	281.4	378.9	329.0	204.4	260.5	173.8	989.3	638.7
Balance at ending of period	8,329.8	8,469.5	8,199.0	7,863.9	7,690.6	7,516.8	8,329.8	7,863.9
Cumulative Effect, Period of Adoption, Adjustment
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period			(1.1)				(1.1)
Common Stock
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2
Balance at beginning of period (in shares)	584.2	584.2	584.2	584.2	584.2	584.2	584.2	584.2
Balance at ending of period	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2	$ 2,921.2
Balance at end of period (in shares)	584.2	584.2	584.2	584.2	584.2	584.2	584.2	584.2
Additional Paid-in Capital
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period	$ 2,312.0	$ 2,297.8	$ 2,323.2	$ 2,286.9	$ 2,277.5	$ 2,286.0	$ 2,323.2	$ 2,286.0
Stock option and incentive plans	7.1	14.2	(25.4)	6.1	9.4	(8.5)
Balance at ending of period	2,319.1	2,312.0	2,297.8	2,293.0	2,286.9	2,277.5	2,319.1	2,293.0
Retained Earnings
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period	5,938.7	5,694.6	5,471.2	5,274.7	5,118.0	5,047.9	5,471.2	5,047.9
Stock option and incentive plans	(0.5)	(0.4)	(0.7)	(0.3)	(0.4)	(0.3)
Dividends declared on common stock; $0.2125 per share	(132.9)	(134.4)	(103.8)	(103.6)	(103.4)	(103.4)
Net income attributable to Conagra Brands, Inc.	281.4	378.9	329.0	204.4	260.5	173.8
Balance at ending of period	6,086.7	5,938.7	5,694.6	5,375.2	5,274.7	5,118.0	6,086.7	5,375.2
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period			(1.1)				(1.1)
Accumulated Other Comprehensive Income (Loss)
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period	(85.1)	(95.8)	(109.6)	(131.0)	(132.4)	(110.3)	(109.6)	(110.3)
Currency translation adjustments	0.1	11.4	15.3	3.9	3.5	(8.9)
Derivative adjustments	(0.1)	(0.1)	(1.2)	(0.9)	(1.4)	(1.8)
Pension and postretirement healthcare benefits	(0.6)	(0.6)	(0.3)	56.0	(0.7)	(11.4)
Balance at ending of period	(85.7)	(85.1)	(95.8)	(72.0)	(131.0)	(132.4)	(85.7)	(72.0)
Treasury Stock
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period	(2,694.8)	(2,696.4)	(2,729.9)	(2,739.7)	(2,744.2)	(2,760.2)	(2,729.9)	(2,760.2)
Stock option and incentive plans	3.4	1.6	33.5	7.3	4.5	16.0
Repurchase of common shares	(298.1)
Balance at ending of period	(2,989.5)	(2,694.8)	(2,696.4)	(2,732.4)	(2,739.7)	(2,744.2)	(2,989.5)	(2,732.4)
Noncontrolling Interests
Schedule Of Stockholders Equity Accounts [Line Items]
Balance at beginning of period	77.5	77.6	74.6	78.5	76.7	79.1	74.6	79.1
Stock option and incentive plans	0.2			0.2		(0.2)
Currency translation adjustments		(0.7)	2.2	(0.1)		(2.7)
Activities of noncontrolling interests	0.3	0.6	0.8	0.3	1.8	0.5
Balance at ending of period	$ 78.0	$ 77.5	$ 77.6	$ 78.9	$ 78.5	$ 76.7	$ 78.0	$ 78.9