Variable Interest Entities (Details) (USD $)	Nov. 30, 2011	Aug. 31, 2011	Nov. 30, 2010	Dec. 31, 2009	Nov. 30, 2009	Dec. 31, 2008
Assets and liabilities of consolidated VIEs prior to consolidation
Cash and cash equivalents	$ 2,393,797,000		$ 2,188,998,000	$ 1,853,167,000	$ 1,853,167,000	$ 1,294,329,000
Total financial instruments owned, at fair value	16,678,541,000		15,941,572,000
Securities borrowed	5,169,689,000		8,152,678,000
Brokers, dealers and clearing organizations	1,235,393,000		2,550,234,000
Other assets	748,072,000		601,799,000
Total assets	34,971,422,000		36,726,543,000	28,121,023,000,000
Total financial instruments sold, not yet purchased, at fair value	6,604,973,000	6,604,973,000	9,109,799,000
Brokers, dealers and clearing organizations	2,816,877,000		1,885,357,000
Mandatorily redeemable preferred interest of consolidated subsidiaries	310,534,000		315,885,000
Total liabilities	31,434,447,000		33,915,578,000
Variable Interest Entities (Textual) [Abstract]
Carrying amount of mandatorily redeemable preferred interest of consolidated subsidiaries	310,534,000		315,885,000
Carrying amount of variable interest as debt, equity and partnership interest	322,000,000		328,200,000
Variable Interest Entity, Primary Beneficiary
Assets and liabilities of consolidated VIEs prior to consolidation
Cash and cash equivalents	345,959,000		202,565,000
Total financial instruments owned, at fair value	712,778,000		1,012,079,000
Brokers, dealers and clearing organizations	150,592,000		195,485,000
Other assets	385,000		370,000
Total assets	1,217,110,000		1,410,626,000
Total financial instruments sold, not yet purchased, at fair value	326,238,000		596,044,000
Brokers, dealers and clearing organizations	105,165,000		157,134,000
Mandatorily redeemable preferred interest of consolidated subsidiaries	310,534,000		315,885,000
Total liabilities	751,677,000		1,163,465,000
Variable Interest Entities (Textual) [Abstract]
Carrying amount of mandatorily redeemable preferred interest of consolidated subsidiaries	310,534,000		315,885,000
Secured financing included in inventory and eliminated	8,400,000		15,700,000
High Yield [Member] | Variable Interest Entity, Primary Beneficiary
Assets and liabilities of consolidated VIEs prior to consolidation
Cash and cash equivalents	345,700,000		202,600,000
Total financial instruments owned, at fair value	693,300,000		889,800,000
Securities borrowed	195,300,000		455,800,000
Brokers, dealers and clearing organizations	150,600,000		195,500,000
Other assets	8,500,000		11,600,000
Total assets	1,393,400,000		1,755,300,000
Total financial instruments sold, not yet purchased, at fair value	326,200,000		602,600,000
Brokers, dealers and clearing organizations	105,200,000		157,100,000
Mandatorily redeemable preferred interest of consolidated subsidiaries	943,400,000		960,200,000
Promissory note	0		0
Secured financing	0		0
Other	20,700,000		36,300,000
Total liabilities	1,395,500,000		1,756,200,000
Variable Interest Entities (Textual) [Abstract]
Carrying amount of mandatorily redeemable preferred interest of consolidated subsidiaries	943,400,000		960,200,000
Mortgage and Asset-backed Securitizations [Member] | Variable Interest Entity, Primary Beneficiary
Assets and liabilities of consolidated VIEs prior to consolidation
Cash and cash equivalents	0		0
Total financial instruments owned, at fair value	12,200,000		101,400,000
Securities borrowed	0		0
Brokers, dealers and clearing organizations	0		0
Other assets	0		100,000
Total assets	12,200,000		101,500,000
Total financial instruments sold, not yet purchased, at fair value	0		0
Brokers, dealers and clearing organizations	0		0
Mandatorily redeemable preferred interest of consolidated subsidiaries	0		0
Promissory note	0		0
Secured financing	12,200,000		101,400,000
Other	0		100,000
Total liabilities	12,200,000		101,500,000
Variable Interest Entities (Textual) [Abstract]
Carrying amount of mandatorily redeemable preferred interest of consolidated subsidiaries	0		0
Other [Member] | Variable Interest Entity, Primary Beneficiary
Assets and liabilities of consolidated VIEs prior to consolidation
Cash and cash equivalents	300,000		0
Total financial instruments owned, at fair value	7,200,000		21,000,000
Securities borrowed	0		0
Brokers, dealers and clearing organizations	0		0
Other assets	0		0
Total assets	7,500,000		21,000,000
Total financial instruments sold, not yet purchased, at fair value	0		0
Brokers, dealers and clearing organizations	0		0
Mandatorily redeemable preferred interest of consolidated subsidiaries	0		0
Promissory note	4,200,000		4,400,000
Secured financing	0		0
Other	200,000		0
Total liabilities	4,400,000		4,400,000
Variable Interest Entities (Textual) [Abstract]
Carrying amount of mandatorily redeemable preferred interest of consolidated subsidiaries	$ 0		$ 0