Variable Interest Entities (Non-Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Financial Statement Carrying Amount, Assets	$ 575.0	$ 579.6
Financial Statement Carrying Amount, Liabilities	0.7	8.9
Maximum Exposure to Loss	1,609.2	1,977.6
VIE Assets	12,221.2	12,386.9
CLOs
Variable Interest Entity [Line Items]
Financial Statement Carrying Amount, Assets	57.0	168.1
Financial Statement Carrying Amount, Liabilities	0.7	8.9
Maximum Exposure to Loss	784.0	1,030.4
VIE Assets	3,348.0	5,364.3
Consumer loan vehicles
Variable Interest Entity [Line Items]
Financial Statement Carrying Amount, Assets	323.5	254.8
Financial Statement Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	602.4	759.8
VIE Assets	3,441.8	2,322.7
Related party private equity vehicles
Variable Interest Entity [Line Items]
Financial Statement Carrying Amount, Assets	34.1	23.7
Financial Statement Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	52.0	45.4
VIE Assets	107.2	75.0
Other private investment vehicles
Variable Interest Entity [Line Items]
Financial Statement Carrying Amount, Assets	160.4	133.0
Financial Statement Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	170.8	142.0
VIE Assets	$ 5,324.2	$ 4,624.9

Variable Interest Entity, Assets of Non Consolidated Vie

No definition available.

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

- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=108788376&loc=d3e5747-111685

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=108788376&loc=d3e5728-111685

+ Details

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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

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Namespace Prefix:	us-gaap_
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Period Type:	duration

- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph a
-URI http://asc.fasb.org/extlink&oid=108788376&loc=d3e5728-111685

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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- Details

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- Details

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- Details

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