Loans to and Investments In Associated Companies (Linkem) (Narrative) (Details) - Linkem $ in Millions	Aug. 31, 2019 USD ($)
Investments In Associated Companies [Line Items]
Equity method investment, ownership percentage	42.00%
Percentage of ownership upon conversion of note	54.00%
Equity method investment, voting percentage	48.00%
Shareholder loans principal outstanding	$ 58.4
Equity Method Investee [Member]
Investments In Associated Companies [Line Items]
Shareholder loans interest rate	5.00%

Equity Method Investment, Shareholder Loans To Investee, Principal Outstanding

No definition available.

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

- Definition

The voting percentage of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

No definition available.

+ Details

Name:	jef_EquityMethodInvestmentVotingPercentage
Namespace Prefix:	jef_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Investments In Associated Companies [Line Items]

+ References

No definition available.

+ Details

Name:	jef_InvestmentsInAssociatedCompaniesLineItems
Namespace Prefix:	jef_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Ownership Percentage Upon Conversion of Preferred Shares

+ References

No definition available.

+ Details

Name:	jef_OwnershipPercentageUponConversionOfPreferredShares
Namespace Prefix:	jef_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Identify the stated interest rate per the agreement, for example, leasing and debt arrangements between related parties.

+ References

No definition available.

+ Details

Name:	us-gaap_RelatedPartyTransactionRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jef_LinkemMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_EquityMethodInvesteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: