Principal amount of each Convertible debenture.

No definition available.

Name:	jef_ConvertibleDebenturePrincipalAmount
Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Debt Instrument, Convertible, Contingent Interest

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Debt Instrument, Convertible, Contingent Interest, Threshold Trading Days

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Convertible, Interest Period

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Convertible, Threshold Of Trading Days

+ References

No definition available.

+ Details

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- Definition

Increase (Decrease) of Long-term Debt

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of debt instrument convertible conversion ratio.

+ References

No definition available.

+ Details

Name:	jef_PercentageOfDebtInstrumentConvertibleConversionRatio
Namespace Prefix:	jef_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Trading price before accruing contingent interest.

+ References

No definition available.

+ Details

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Namespace Prefix:	jef_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Trading days consider for lower range of stock price.

+ References

No definition available.

+ Details

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

- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Conversion Rate
-URI http://asc.fasb.org/extlink&oid=6509012

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(5))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Balance Type:	na
Period Type:	duration

- Definition

Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instruments must exceed threshold percentage for a specified number of trading days to trigger conversion feature, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

+ References

No definition available.

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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-Name Accounting Standards Codification
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-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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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

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Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
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-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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- Details

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Long-Term Debt - Additional Information (Detail)		9 Months Ended
Long-Term Debt - Additional Information (Detail)	Sep. 14, 2017 USD ($) $ / shares	Aug. 31, 2017 USD ($)	Jan. 17, 2017 USD ($)	Nov. 30, 2016 USD ($)	Aug. 31, 2016 USD ($)	Jan. 21, 2016 USD ($)
Debt Instrument [Line Items]
Long-term debt at fair value		$ 553,870,000		$ 248,856,000
Long-term debt		6,449,685,000		5,483,355,000
Leucadia \| Subsequent event
Debt Instrument [Line Items]
Debenture principal amount	$ 1,000
Debt instrument convertible conversion ratio	22.9719
Conversion price of common stock (dollars per share) \| $ / shares	$ 43.53
Senior Notes
Debt Instrument [Line Items]
Debt principal amount		641,000,000.0
Class A Notes, Due 2022
Debt Instrument [Line Items]
Long-term debt						$ 15,000,000.0
Class B Notes, Due 2022
Debt Instrument [Line Items]
Long-term debt						$ 7,500,000
4.850% Senior Notes \| Unsecured Debt
Debt Instrument [Line Items]
Debt principal amount			$ 750,000,000.0
Long-term debt		$ 753,932,000		0
Debt instrument interest rate		4.85%
3.875% Convertible Senior Debentures
Debt Instrument [Line Items]
Debt principal amount		$ 345,000,000.0
3.875% Convertible Senior Debentures \| Leucadia
Debt Instrument [Line Items]
Debt instrument interest rate		3.875%
Debt instrument convertible conversion ratio (greater than)		130.00%
Earliest period of conversion price		20 days
Latest period of conversion price		30 days
Less than trading price per debenture related to common stock		95.00%
Consecutive trading days		10 days
Contingent interest		0.375%
Threshold trading days		5 days
Interest period		6 months
Trading price of contingent interest		$ 1,200
3.875% Convertible Senior Debentures \| Unsecured Debt
Debt Instrument [Line Items]
Long-term debt		$ 345,217,000		346,187,000
Debt instrument interest rate		3.875%
Structured notes
Debt Instrument [Line Items]
Long-term debt		$ 561,010,000		255,203,000
Structured notes \| Unsecured Debt
Debt Instrument [Line Items]
Debt principal amount		287,500,000			$ 222,700,000
Long-term debt at fair value		553,900,000		$ 248,900,000
Interest rate swaps \| 4.850% Senior Notes \| Unsecured Debt
Debt Instrument [Line Items]
Decrease of long-term debt		$ (9,600,000)