Derivative Financial Instruments - Remaining Contract Maturity of Fair Value of OTC Derivative Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2014
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	$ 226,599
OTC derivative assets having maturity period of 1 to 5 years	130,800
OTC derivative assets having maturity period of greater than 5 years	129,269
OTC derivative assets cross-maturity netting	(84,660)
Total OTC derivative assets, net of cross-maturity netting	402,008
Cross product counterparty netting	(17,810)
Total OTC derivative assets included in Financial instruments owned	384,198
OTC derivative liabilities having maturity period of 0 to 12 months	225,317
OTC derivative liabilities having maturity period of 1 to 5 years	145,975
OTC derivative liabilities having maturity period of greater than 5 years	176,850
OTC derivative liabilities cross-maturity netting	(84,660)
Total OTC derivative liabilities, net of cross-maturity netting	463,482
Total OTC derivative liabilities included in Financial instruments sold, not yet purchased	445,672
Commodity swaps, options and forwards [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	52,226
OTC derivative assets having maturity period of 1 to 5 years	1,435
Total OTC derivative assets, net of cross-maturity netting	53,661
OTC derivative liabilities having maturity period of 0 to 12 months	78,158
OTC derivative liabilities having maturity period of 1 to 5 years	9,117
Total OTC derivative liabilities, net of cross-maturity netting	87,275
Credit default swaps [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative liabilities having maturity period of 0 to 12 months	51
OTC derivative liabilities having maturity period of 1 to 5 years	8,744
OTC derivative liabilities having maturity period of greater than 5 years	898
Total OTC derivative liabilities, net of cross-maturity netting	9,693
Equity swaps and options [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	1,297
Total OTC derivative assets, net of cross-maturity netting	1,297
OTC derivative liabilities having maturity period of greater than 5 years	9,300
Total OTC derivative liabilities, net of cross-maturity netting	9,300
Total return swaps [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	6,559
Total OTC derivative assets, net of cross-maturity netting	6,559
OTC derivative liabilities having maturity period of 0 to 12 months	2,200
Total OTC derivative liabilities, net of cross-maturity netting	2,200
Foreign currency forwards, swaps and options [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	85,715
OTC derivative assets having maturity period of 1 to 5 years	15,283
OTC derivative assets having maturity period of greater than 5 years	51
OTC derivative assets cross-maturity netting	(14,167)
Total OTC derivative assets, net of cross-maturity netting	86,882
OTC derivative liabilities having maturity period of 0 to 12 months	88,516
OTC derivative liabilities having maturity period of 1 to 5 years	16,380
OTC derivative liabilities cross-maturity netting	(14,167)
Total OTC derivative liabilities, net of cross-maturity netting	90,729
Interest rate swaps, options and forwards [Member]
Remaining Contract Maturity Of Fair Value Of Over Counter Derivative Assets And Liabilities [Line Items]
OTC derivative assets having maturity period of 0 to 12 months	80,802
OTC derivative assets having maturity period of 1 to 5 years	114,082
OTC derivative assets having maturity period of greater than 5 years	129,218
OTC derivative assets cross-maturity netting	(70,493)
Total OTC derivative assets, net of cross-maturity netting	253,609
OTC derivative liabilities having maturity period of 0 to 12 months	56,392
OTC derivative liabilities having maturity period of 1 to 5 years	111,734
OTC derivative liabilities having maturity period of greater than 5 years	166,652
OTC derivative liabilities cross-maturity netting	(70,493)
Total OTC derivative liabilities, net of cross-maturity netting	$ 264,285