Commitments, Contingencies and Guarantees - Additional Information (Detail) £ in Millions, $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2016 GBP (£)	Feb. 29, 2016 USD ($)
Loss Contingencies [Line Items]
Loan commitments outstanding to clients		$ 139.2
Fair value of mortgage-related commitments		145.7
Fair value of derivative contracts approximated deemed to meet the definition of a guarantee		429.0
Maximum amount payable under guarantee		21.5
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Letters of credit commitments		$ 33.7
Standby letters of credit expiration period		1 year
Jefferies Capital Partners LLC [Member]
Loss Contingencies [Line Items]
Outstanding equity commitments		$ 23.3
Other Investments [Member]
Loss Contingencies [Line Items]
Outstanding equity commitments		$ 4.3
Subsequent event [Member]
Loss Contingencies [Line Items]
Contractual obligation | £	£ 8.1
Contractual obligation period for 18 years	18 years