Derivative Financial Instruments - Counterparty Credit Quality with Respect to Fair Value of OTC Derivatives Assets (Detail) $ in Thousands	May 31, 2019 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
A- or higher	$ 73,860
BBB- to BBB	18,788
BB or lower	194,336
Unrated	131,239
Total OTC derivative assets included in Financial instruments owned	$ 418,223

Fair value of OTC derivatives assets, counterparty credit quality BB or lower.

No definition available.

Name:	jef_FairValueOfOverCounterDerivativesAssetsCounterpartyCreditQualityBbOrLower
Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair value of OTC derivatives assets, counterparty credit quality BBB- to BBB.

No definition available.

Name:	jef_FairValueOfOverCounterDerivativesAssetsCounterpartyCreditQualityBbbToBbb
Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair value of OTC derivatives assets, counterparty credit quality unrated.

No definition available.

Name:	jef_FairValueOfOverCounterDerivativesAssetsCounterpartyCreditQualityUnrated
Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair Value Of Over Counter Derivatives Assets Counterparty Credit QualityA Or Higher

No definition available.

Name:	jef_FairValueOfOverCounterDerivativesAssetsCounterpartyCreditQualityaOrHigher
Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

OTC Derivative Assets Included In Financial Instruments Owned.

No definition available.

Name:	jef_OtcDerivativeAssetsIncludedInFinancialInstrumentsOwned
Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

No definition available.

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