Investments - Jefferies LoanCore - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2015	May. 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			125.6		$ 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	$ 16.8	$ 6.8	$ 36.8	$ 11.8
Placement fees earned	$ 0.2	$ 0.3	$ 0.6	$ 0.6