Derivative Financial Instruments (Fair Value and Related Number of Derivative Contracts Categorized by Predominant Risk Exposure) (Details) $ in Thousands	May 31, 2020 USD ($) Contract	Nov. 30, 2019 USD ($) Contract
Derivatives, Fair Value [Line Items]
Net amounts per consolidated statement of financial condition, assets	$ 640,593	$ 418,408
Net amounts per consolidated statement of financial condition, liabilities	417,900	527,205
Cleared OTC
Derivatives, Fair Value [Line Items]
Fair value, assets	300,665	244,401
Fair value, liabilities	327,390	290,201
Amounts offset in consolidated statement of financial condition, assets	(286,069)	(222,869)
Amounts offset in consolidated statement of financial condition, liabilities	(287,244)	(266,900)
Exchange-traded
Derivatives, Fair Value [Line Items]
Fair value, assets	422,892	718,685
Fair value, liabilities	502,252	962,638
Amounts offset in consolidated statement of financial condition, assets	(409,622)	(688,871)
Amounts offset in consolidated statement of financial condition, liabilities	(409,622)	(688,871)
Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair value, assets	1,445,376	888,519
Fair value, liabilities	1,271,141	906,544
Amounts offset in consolidated statement of financial condition, assets	(832,649)	(521,457)
Amounts offset in consolidated statement of financial condition, liabilities	(986,017)	(676,407)
Designated as accounting hedges \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	74,227	28,663
Fair value, liabilities	0	0
Designated as accounting hedges \| Cleared OTC \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 74,227	$ 28,663
Number of contracts, assets \| Contract	1	1
Fair value, liabilities	$ 0	$ 0
Number of contracts, liabilities \| Contract	0	0
Not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 2,094,706	$ 1,822,942
Fair value, liabilities	2,100,783	2,159,383
Not designated as accounting hedges \| Cleared OTC \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 226,248	$ 213,224
Number of contracts, assets \| Contract	4,332	3,329
Fair value, liabilities	$ 326,475	$ 284,433
Number of contracts, liabilities \| Contract	4,585	3,443
Not designated as accounting hedges \| Cleared OTC \| Credit contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 190	$ 2,514
Number of contracts, assets \| Contract	14	13
Fair value, liabilities	$ 915	$ 5,768
Number of contracts, liabilities \| Contract	6	12
Not designated as accounting hedges \| Exchange-traded \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 515	$ 1,191
Number of contracts, assets \| Contract	43,775	65,226
Fair value, liabilities	$ 277	$ 103
Number of contracts, liabilities \| Contract	56,844	38,464
Not designated as accounting hedges \| Exchange-traded \| Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 0	$ 0
Number of contracts, assets \| Contract	0	256
Fair value, liabilities	$ 0	$ 0
Number of contracts, liabilities \| Contract	139	199
Not designated as accounting hedges \| Exchange-traded \| Equity contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 422,377	$ 717,494
Number of contracts, assets \| Contract	986,001	1,714,538
Fair value, liabilities	$ 501,975	$ 962,535
Number of contracts, liabilities \| Contract	872,216	1,481,388
Not designated as accounting hedges \| Exchange-traded \| Commodity contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 0	$ 0
Number of contracts, assets \| Contract	3,251	5,524
Fair value, liabilities	$ 0	$ 0
Number of contracts, liabilities \| Contract	4,572	4,646
Not designated as accounting hedges \| Bilateral OTC \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 732,046	$ 421,700
Number of contracts, assets \| Contract	1,244	1,325
Fair value, liabilities	$ 315,023	$ 258,857
Number of contracts, liabilities \| Contract	601	738
Not designated as accounting hedges \| Bilateral OTC \| Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 324,486	$ 191,218
Number of contracts, assets \| Contract	12,874	9,257
Fair value, liabilities	$ 342,011	$ 187,836
Number of contracts, liabilities \| Contract	12,671	9,187
Not designated as accounting hedges \| Bilateral OTC \| Equity contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 330,034	$ 248,720
Number of contracts, assets \| Contract	1,398	4,731
Fair value, liabilities	$ 610,146	$ 445,241
Number of contracts, liabilities \| Contract	1,574	4,271
Not designated as accounting hedges \| Bilateral OTC \| Commodity contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 55,113	$ 20,600
Number of contracts, assets \| Contract	2,968	4,084
Fair value, liabilities	$ 0	$ 391
Number of contracts, liabilities \| Contract	0	359
Not designated as accounting hedges \| Bilateral OTC \| Credit contracts
Derivatives, Fair Value [Line Items]
Fair value, assets	$ 3,697	$ 6,281
Number of contracts, assets \| Contract	11	25
Fair value, liabilities	$ 3,961	$ 14,219
Number of contracts, liabilities \| Contract	7	28

Derivative, Fair Value of Derivative Asset, Amount Netting in Consolidated Statement of Financial Condition

No definition available.

Name:	jef_DerivativeFairValueOfDerivativeAssetAmountNettingInConsolidatedStatementOfFinancialCondition
Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Derivative, Fair Value of Derivative Liability, Amount Netting in Consolidated Statement of Financial Condition

+ References

No definition available.

+ Details

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

- Definition

The number of derivative instruments of a particular derivative asset or group of derivative assets held by the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeAssetNumberOfInstrumentsHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

Name:	us-gaap_DerivativeAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624163-113959

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624163-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The number of derivative instruments of a particular derivative liability or group of derivative liabilities held by the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeLiabilityNumberOfInstrumentsHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_InvestmentTypeAxis=jef_ClearedOTCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ExchangeTradedOptionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=jef_BilateralOTCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=jef_CreditContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_EquityContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CommodityContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: