Loans to and Investments In Associated Companies (Jefferies Finance) (Narrative) (Details) - USD ($)		3 Months Ended		6 Months Ended
	May 15, 2019	May 31, 2019	Jun. 30, 2018	May 31, 2019	Jun. 30, 2018	Mar. 28, 2019	Nov. 30, 2018
Investments In Associated Companies [Line Items]
Other		$ 1,985,328,000		$ 1,985,328,000			$ 1,859,561,000
Payables, expense accruals and other liabilities		7,029,001,000		7,029,001,000			7,407,030,000
Trading liabilities, at fair value		10,113,390,000		10,113,390,000			9,478,946,000
Interest expense		23,138,000	$ 24,279,000	46,156,000	$ 45,777,000
Jefferies Group
Investments In Associated Companies [Line Items]
Interest income and unfunded commitment fees related to facility commitment		300,000	700,000	600,000	1,700,000
Investment banking		69,300,000	109,600,000	91,200,000	211,000,000.0
Origination fees		8,200,000	14,900,000	13,600,000	33,400,000
Placement agent fees		0.0	2,400,000	1,300,000	2,700,000
Underwriting fees income		1,000,000.0		1,000,000.0
Service fee income		11,200,000	8,900,000	38,300,000	35,000,000.0
Interest expense		$ 408,714,000	$ 332,667,000	$ 775,283,000	$ 598,343,000
Jefferies Finance
Investments In Associated Companies [Line Items]
Equity method investment, ownership percentage		50.00%		50.00%
Equity commitment		$ 750,000,000.0		$ 750,000,000.0
Funded equity commitments		643,700,000		$ 643,700,000
Investment commitment extension				1 year
Termination notice				60 days
Total line of credit facility commitment under joint venture		500,000,000.0		$ 500,000,000.0			500,000,000.0
Extension period				1 year
Line of credit facility, commitment of Jefferies, funded		0		$ 0			0
Line of credit facility commitment of Jefferies		250,000,000.0		250,000,000.0			250,000,000.0
Other		20,400,000		20,400,000			35,200,000
Payables, expense accruals and other liabilities		13,700,000		13,700,000			14,100,000
Foreign exchange contracts | Jefferies Finance
Investments In Associated Companies [Line Items]
Payables, expense accruals and other liabilities							200,000
Trading liabilities, at fair value		$ 100,000		$ 100,000			$ 400,000
Promissory Note | Jefferies Group
Investments In Associated Companies [Line Items]
Debt principal amount						$ 1,000,000,000.0
Interest expense	$ 3,800,000