Risk Management Activities (Schedule of unallocated corporate items) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Nov. 25, 2018	Nov. 26, 2017	Nov. 25, 2018	Nov. 26, 2017
Commodity Price Risk [Abstract]
Net gain (loss) on mark-to-market valuation of certain commodity positions	$ (17.5)	$ (0.6)	$ (37.0)	$ (8.4)
Net loss (gain) on commodity positions reclassified from unallocated corporate items to segment operating profit	2.2	2.5	(1.5)	6.1
Net mark-to-market revaluation of certain grain inventories	3.5	2.6	(4.4)	8.6
Net mark-to-market valuation of certain commodity positions recognized in unallocated corporate items	$ (11.8)	$ 4.5	$ (42.9)	$ 6.3

The amount of (gain) loss from commodity positions that was reclassified from unallocated corporate items to segment operating profit.

No definition available.

+ Details

Name:	gis_NetLossGainOnCommodityPositionsReclassifiedFromUnallocatedCorporateItemsToSegmentOperatingProfit
Namespace Prefix:	gis_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in corporate unallocated items relating to net gain (loss) on mark to market valuation of commodity positions and certain grain inventories net of net realized gain (loss) on these positions reclassified to segment operating profit.

+ References

No definition available.

+ Details

Name:	gis_NetMarkToMarketValuationOfCertainCommodityPositionsRecognizedInUnallocatedCorporateItems
Namespace Prefix:	gis_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of price risk derivatives not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

+ Details

Name:	us-gaap_GainLossOnPriceRiskDerivativeInstrumentsNotDesignatedAsHedgingInstruments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of unrealized gain (loss) recognized in earnings related to the fair value of the hedged item in a price risk fair value hedge, offset by the gain (loss) on the hedging instrument to the extent that the fair value hedge is determined to be effective.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

+ Details

Name:	us-gaap_IncreaseDecreaseInFairValueOfHedgedItemInPriceRiskFairValueHedge1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_PriceRiskDerivativesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration