Investments - Jefferies LoanCore - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2015	Aug. 31, 2014	Aug. 31, 2015	Aug. 31, 2014	Nov. 30, 2014	Feb. 23, 2011
Guarantee Obligations [Line Items]
Equity commitment	$ 600.0		$ 600.0
Jefferies LoanCore, LLC [Member]
Guarantee Obligations [Line Items]
Aggregate commitment						$ 600.0
Funded portion of equity commitment to subsidiary			118.4		$ 200.9
Equity commitment	$ 291.0		$ 291.0
Percentage of the Variable Interest Entity's (VIE) voting interest	48.50%		48.50%
Net earnings from equity method investment	$ 25.6	$ 4.5	$ 62.4	$ 16.3
Placement fees earned	$ 1.0	$ 0.0	$ 1.6	$ 0.6