Variable Interest Entities - Assets and Liabilities of Consolidated VIEs Prior to Consolidation (Detail) - USD ($) $ in Millions	Aug. 31, 2015	Nov. 30, 2014
Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Assets	$ 823.5	$ 638.3
Liabilities	823.5	638.3
Other [Member]
Variable Interest Entity [Line Items]
Assets	0.5	0.5
Liabilities	0.2	0.2
Cash [Member] | Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Assets	0.1	0.0
Cash [Member] | Other [Member]
Variable Interest Entity [Line Items]
Assets	0.2	0.2
Financial Instruments Owned [Member] | Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Assets	86.4	62.7
Financial Instruments Owned [Member] | Other [Member]
Variable Interest Entity [Line Items]
Assets	0.3	0.3
Securities Purchased Under Agreement to Resell [Member] | Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Assets	736.7	575.2
Securities Purchased Under Agreement to Resell [Member] | Other [Member]
Variable Interest Entity [Line Items]
Assets	0.0	0.0
Fees, Interest and Other Receivables [Member] | Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Assets	0.3	0.4
Fees, Interest and Other Receivables [Member] | Other [Member]
Variable Interest Entity [Line Items]
Assets	0.0	0.0
Other Secured Financings [Member] | Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Liabilities	822.5	637.7
Other Secured Financings [Member] | Other [Member]
Variable Interest Entity [Line Items]
Liabilities	0.0	0.0
Other Liabilities [Member] | Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Liabilities	1.0	0.6
Other Liabilities [Member] | Other [Member]
Variable Interest Entity [Line Items]
Liabilities	$ 0.2	$ 0.2