Commitments, Contingencies and Guarantees (Narrative) (Details)	6 Months Ended
	May 31, 2020 USD ($)
Loss Contingencies [Line Items]
Loan commitments outstanding to clients	$ 80,000,000.0
Fair value of derivative contracts meeting the definition of a guarantee	192,700,000
Standby letters of credit
Loss Contingencies [Line Items]
Letters of credit	$ 38,500,000
Expiration period maximum	1 year
Jefferies Finance
Loss Contingencies [Line Items]
Line of credit commitment to associated companies, funded portion	$ 20,000,000.0
Line of credit facility commitment of Jefferies	250,000,000.0
Berkadia
Loss Contingencies [Line Items]
Surety policy issued	$ 1,500,000,000
Reimbursement of losses incurred, maximum percentage	50.00%
Aggregate amount of commercial paper outstanding	$ 1,470,000,000
HomeFed
Loss Contingencies [Line Items]
Aggregate amount of infrastructure improvement bonds outstanding	66,600,000
Jefferies Capital Partners LLC and its private equity funds
Loss Contingencies [Line Items]
Equity commitments	11,300,000
Other Investments
Loss Contingencies [Line Items]
Equity commitments	$ 225,700,000