Commitments, Contingencies and Guarantees - Commitments (Details) $ in Millions	9 Months Ended
Aug. 31, 2020 USD ($)
Commitments and Guarantees Obligations [Line Items]
2020	$ 10,119.5
2021	638.1
2022 and 2023	36.4
2024 and 2025	5.1
2026 and Later	7.2
Maximum Payout	$ 10,806.3
Repos Obligation Settlement Period	3 days
Equity commitments
Commitments and Guarantees Obligations [Line Items]
2020	$ 0.2
2021	106.7
2022 and 2023	1.4
2024 and 2025	0.0
2026 and Later	7.2
Maximum Payout	115.5
Loan commitments
Commitments and Guarantees Obligations [Line Items]
2020	0.0
2021	295.0
2022 and 2023	35.0
2024 and 2025	0.0
2026 and Later	0.0
Maximum Payout	330.0
Underwriting commitments
Commitments and Guarantees Obligations [Line Items]
2020	64.0
2021	0.0
2022 and 2023	0.0
2024 and 2025	0.0
2026 and Later	0.0
Maximum Payout	64.0
Forward starting reverse repos
Commitments and Guarantees Obligations [Line Items]
2020	6,184.5
2021	0.0
2022 and 2023	0.0
2024 and 2025	0.0
2026 and Later	0.0
Maximum Payout	6,184.5
Forward starting repos
Commitments and Guarantees Obligations [Line Items]
2020	3,870.8
2021	100.0
2022 and 2023	0.0
2024 and 2025	0.0
2026 and Later	0.0
Maximum Payout	3,970.8
Other unfunded commitments
Commitments and Guarantees Obligations [Line Items]
2020	0.0
2021	136.4
2022 and 2023	0.0
2024 and 2025	5.1
2026 and Later	0.0
Maximum Payout	141.5
Forward starting securities purchased under agreements to resell settled
Commitments and Guarantees Obligations [Line Items]
Maximum Payout	6,183.8
Forward starting securities sold under agreements to repurchase settled
Commitments and Guarantees Obligations [Line Items]
Maximum Payout	$ 3,670.6

Repos Obligation Settlement Period

No definition available.

Name:	jef_ReposObligationSettlementPeriod
Namespace Prefix:	jef_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in fourth and fifth fiscal years following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in second and third fiscal years following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in remainder of current fiscal year.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligationFutureMinimumPaymentsDueRemainderOfFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_OtherCommitmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_EquityCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_LoanCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_UnderwritingCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_ForwardStartingReverseReposMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_ForwardStartingReposMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_OtherCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_ForwardStartingSecuritiesPurchasedUnderAgreementsToResellSettledMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=jef_ForwardStartingSecuritiesSoldUnderAgreementsToRepurchaseSettledMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: