Fair Value Disclosures - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Nov. 30, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	$ 100,500,000	$ 109,900,000
Transfers of assets from Level 3 to Level 2	112,700,000	41,500,000
Transfers of liabilities from Level 3 to Level 2	700,000	2,200,000
Net gains/losses on Level 3 assets (realized and unrealized)	14,500,000	(9,700,000)
Net gains/losses on Level 3 liabilities (realized and unrealized)	(2,700,000)	(1,500,000)
Unadjusted net asset value of the funds	68,100,000		82,700,000
Residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	78,400,000	32,500,000
Transfers of assets from Level 3 to Level 2	73,500,000	6,600,000
Commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	1,300,000	1,500,000
Transfers of assets from Level 3 to Level 2	10,900,000	12,800,000
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	10,800,000	8,600,000
Transfers of assets from Level 3 to Level 2		500,000
Corporate equity securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	100,000	900,000
Transfers of assets from Level 3 to Level 2	4,700,000
Collateralized debt obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	5,300,000	42,800,000
Transfers of assets from Level 3 to Level 2	2,400,000
Other asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3		4,700,000
Transfers of assets from Level 3 to Level 2	200,000	2,300,000
Loans and other receivables [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	4,800,000	18,400,000
Transfers of assets from Level 3 to Level 2	19,900,000	13,900,000
Municipal Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3		500,000
Transfers of assets from Level 3 to Level 2		$ 5,400,000