Derivative Financial Instruments - Fair Value and Related Number of Derivative Contracts Categorized by Type of Derivative Contract (Details) $ in Thousands	Aug. 31, 2020 USD ($) Contract	Nov. 30, 2019 USD ($) Contract
Derivatives, Fair Value [Line Items]
Net amounts per Consolidated Statements of Financial Condition, Assets	$ 504,237	$ 397,551
Net amounts per Consolidated Statements of Financial Condition, Liabilities	483,224	527,205
Exchange-traded
Derivatives, Fair Value [Line Items]
Fair Value, Assets	507,864	718,685
Fair Value, Liabilities	517,457	962,638
Amounts offset in the Consolidated Statements of Financial Condition, Assets	(504,400)	(688,871)
Amounts offset in the Consolidated Statements of Financial Condition, Liabilities	(504,400)	(688,871)
Cleared OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	148,449	244,401
Fair Value, Liabilities	174,034	290,201
Amounts offset in the Consolidated Statements of Financial Condition, Assets	(144,200)	(222,869)
Amounts offset in the Consolidated Statements of Financial Condition, Liabilities	(145,706)	(266,900)
Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	1,459,739	867,271
Fair Value, Liabilities	1,591,414	906,153
Amounts offset in the Consolidated Statements of Financial Condition, Assets	(963,215)	(521,066)
Amounts offset in the Consolidated Statements of Financial Condition, Liabilities	(1,149,575)	(676,016)
Derivatives designated as accounting hedges
Derivatives, Fair Value [Line Items]
Fair Value, Assets	70,159	28,663
Fair Value, Liabilities	393	0
Derivatives designated as accounting hedges \| Interest rate contracts \| Cleared OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 70,159	$ 28,663
Number of Contracts, Assets \| Contract	1	1
Fair Value, Liabilities	$ 0	$ 0
Number of Contracts, Liabilities \| Contract	0	0
Derivatives designated as accounting hedges \| Foreign exchange contracts \| Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 0
Number of Contracts, Assets \| Contract	0
Fair Value, Liabilities	$ 393
Number of Contracts, Liabilities \| Contract	2
Derivatives not designated as accounting hedges
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 2,045,893	$ 1,801,694
Fair Value, Liabilities	2,282,512	2,158,992
Derivatives not designated as accounting hedges \| Interest rate contracts \| Exchange-traded
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 781	$ 1,191
Number of Contracts, Assets \| Contract	48,453	65,226
Fair Value, Liabilities	$ 73	$ 103
Number of Contracts, Liabilities \| Contract	69,918	38,464
Derivatives not designated as accounting hedges \| Interest rate contracts \| Cleared OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 75,125	$ 213,224
Number of Contracts, Assets \| Contract	3,894	3,329
Fair Value, Liabilities	$ 168,467	$ 284,433
Number of Contracts, Liabilities \| Contract	4,199	3,443
Derivatives not designated as accounting hedges \| Interest rate contracts \| Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 689,581	$ 421,700
Number of Contracts, Assets \| Contract	1,480	1,325
Fair Value, Liabilities	$ 316,196	$ 258,857
Number of Contracts, Liabilities \| Contract	621	738
Derivatives not designated as accounting hedges \| Foreign exchange contracts \| Exchange-traded
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	245	199
Derivatives not designated as accounting hedges \| Foreign exchange contracts \| Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 416,298	$ 190,570
Number of Contracts, Assets \| Contract	13,561	9,255
Fair Value, Liabilities	$ 391,431	$ 187,836
Number of Contracts, Liabilities \| Contract	13,449	9,187
Derivatives not designated as accounting hedges \| Equity contracts \| Exchange-traded
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 507,083	$ 717,494
Number of Contracts, Assets \| Contract	906,465	1,714,538
Fair Value, Liabilities	$ 517,384	$ 962,535
Number of Contracts, Liabilities \| Contract	775,309	1,481,388
Derivatives not designated as accounting hedges \| Equity contracts \| Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 351,744	$ 248,720
Number of Contracts, Assets \| Contract	1,939	4,731
Fair Value, Liabilities	$ 879,876	$ 445,241
Number of Contracts, Liabilities \| Contract	1,945	4,271
Derivatives not designated as accounting hedges \| Commodity contracts \| Exchange-traded
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 0	$ 0
Number of Contracts, Assets \| Contract	2,073	5,524
Fair Value, Liabilities	$ 0	$ 0
Number of Contracts, Liabilities \| Contract	1,503	4,646
Derivatives not designated as accounting hedges \| Commodity contracts \| Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 0
Number of Contracts, Assets \| Contract	1
Fair Value, Liabilities	$ 0
Number of Contracts, Liabilities \| Contract	0
Derivatives not designated as accounting hedges \| Credit contracts \| Cleared OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 3,165	$ 2,514
Number of Contracts, Assets \| Contract	15	13
Fair Value, Liabilities	$ 5,567	$ 5,768
Number of Contracts, Liabilities \| Contract	13	12
Derivatives not designated as accounting hedges \| Credit contracts \| Bilateral OTC
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 2,116	$ 6,281
Number of Contracts, Assets \| Contract	11	25
Fair Value, Liabilities	$ 3,518	$ 14,219
Number of Contracts, Liabilities \| Contract	10	28

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

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, 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, after effects of master netting arrangements, of 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 offset against an obligation to return collateral. 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 50
-Paragraph 3
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=d3e41678-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
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 effects of master netting arrangements, of 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 offset against the right to receive collateral. 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 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=d3e41678-113959

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 (e)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
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

- Definition

The fair value as of the balance sheet date of firm holdings in all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments. Their value is derived from the values of one or more underlying assets, reference rates, or indices of asset values. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph c
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624163-113959

+ Details

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

- Definition

Fair value of obligations arising from derivatives and other contracts sold short.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 35
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35711043&loc=d3e42429-110968

+ Details

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

- Details

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

- Details

Name:	us-gaap_InvestmentTypeAxis=jef_OtcClearedMember
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_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
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=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:

- Details

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