Fair Value Disclosures (Fair Value Option Election Narrative) (Details) $ in Thousands, shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) director shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) director shares	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jul. 13, 2018	Jul. 12, 2018	Dec. 31, 2017 USD ($) shares
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Financial instruments owned trading assets, at fair value	$ 17,709,245		$ 17,709,245						$ 16,082,676
Jefferies Group
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Loans and other receivables on nonaccrual status and/or 90 days or greater past due	77,000		77,000						55,100
Loans and other receivables 90 days or greater past due	25,600		25,600						37,400
KCG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Changes in fair value of investments reflected as principal transactions		$ 2,200			$ 93,400
HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Cash consideration paid for shares	475,600		475,600
HRG Group/Spectrum Brands Holdings, Inc.
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Changes in fair value of investments reflected as principal transactions	(48,500)	$ (97,900)	(228,400)		$ 2,300
Spectrum Brands
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Financial instruments owned trading assets, at fair value	$ 561,500		$ 561,500						$ 789,900
Revenue of investee				$ 2,358,100		$ 2,222,700
Net income from continuing operations of investee				443,700		(46,000)
Net income (loss) of investee				941,600		249,200
Net income (loss) attributable to HRG				$ 847,700		$ 132,200
Number of directors appointed by Company | director	1		1
Spectrum Brands
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Shares owned, number | shares	7.5		7.5
Percentage of ownership owned	14.00%		14.00%				14.00%
Spectrum Brands | HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Percentage of ownership owned							62.00%
HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Shares owned, number | shares									46.6
Percentage of outstanding common stock owned									23.00%
Percentage of ownership owned								23.00%	23.00%