Fair Value Disclosures (Schedule Of Assets And Liabilities Measured On Recurring Basis At Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value based on NAV	$ 29,500	$ 36,700
Derivatives	355,400	262,799
Counterparty/cash-collateral netting, Assets	(5,887,874)	(4,165,446)
Total trading assets, excluding Investments at fair value based on NAV	15,567,743	18,256,356
Total available for sale securities	350,666	207,355
Cash and cash equivalents	3,278,975	3,638,648
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	1,026,865	751,084
Derivatives	390,769	218,243
Counterparty/cash-collateral netting, Liabilities	(5,970,029)	(4,257,998)
Total trading liabilities	7,999,156	6,840,430
Other secured financings	53,586	68,345
Debt-structured notes	204,422
Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	1,777,506	1,464,604
Corporate debt securities	1,705,150	1,556,941
U.S. government and federal agency securities	1,213,672	1,488,121
Sovereign obligations	2,373,031	1,342,996
Loans	539,028	769,408
Derivatives	390,769	218,243
Counterparty/cash-collateral netting, Liabilities	(5,970,029)	(4,257,998)
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	99,900
Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	2,971,112	2,977,881
Corporate debt securities	2,529,310	2,893,041
CDOs and CLOs	143,864	174,236
U.S. government and federal agency securities	3,143,852	2,645,651
Municipal securities	577,467	487,141
Sovereign obligations	2,035,035	2,659,441
Loans and other receivables	1,401,549	1,312,333
Derivatives	355,400	262,799
Counterparty/cash-collateral netting, Assets	(5,887,874)	(4,165,446)
Investments at fair value	300,909	226,018
Investment in FXCM, Fair value of senior secured term loan receivable	207,400
Investment in FXCM, Fair value of senior secured term loan receivable and rights to future distributions		625,689
Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	77,372	73,579
Corporate debt securities	1,519	4,744
U.S. government and federal agency securities	226,093	63,945
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading assets, excluding Investments at fair value based on NAV	6,774,924	6,611,880
Total available for sale securities	303,465	137,524
Cash and cash equivalents	3,278,975	3,638,648
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	1,026,865	751,084
Total trading liabilities	3,873,130	3,754,147
Other secured financings	0	0
Debt-structured notes	0
Level 1 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	1,718,634	1,428,048
Corporate debt securities	0	0
U.S. government and federal agency securities	1,213,672	1,488,121
Sovereign obligations	940,451	837,614
Loans	0	0
Derivatives	373	364
Level 1 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	2,837,849	2,803,243
Corporate debt securities	0	0
CDOs and CLOs	0	0
U.S. government and federal agency securities	3,029,251	2,555,018
Municipal securities	0	0
Sovereign obligations	904,592	1,251,366
Loans and other receivables	0	0
Derivatives	3,232	2,253
Investments at fair value	0	0
Investment in FXCM, Fair value of senior secured term loan receivable	0
Investment in FXCM, Fair value of senior secured term loan receivable and rights to future distributions		0
Level 1 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	77,372	73,579
Corporate debt securities	0	0
U.S. government and federal agency securities	226,093	63,945
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading assets, excluding Investments at fair value based on NAV	13,823,252	14,495,857
Total available for sale securities	47,201	69,831
Cash and cash equivalents	0	0
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	0	0
Total trading liabilities	10,074,039	7,314,231
Other secured financings	53,318	67,801
Debt-structured notes	204,422
Level 2 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	58,834	36,518
Corporate debt securities	1,704,627	1,556,941
U.S. government and federal agency securities	0	0
Sovereign obligations	1,432,580	505,382
Loans	538,180	758,939
Derivatives	6,339,818	4,456,334
Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	111,068	133,732
Corporate debt securities	2,494,303	2,867,165
CDOs and CLOs	99,794	89,144
U.S. government and federal agency securities	114,601	90,633
Municipal securities	550,210	487,141
Sovereign obligations	1,130,443	1,407,955
Loans and other receivables	1,323,092	1,123,044
Derivatives	6,230,482	4,406,207
Investments at fair value	0	26,224
Investment in FXCM, Fair value of senior secured term loan receivable	0
Investment in FXCM, Fair value of senior secured term loan receivable and rights to future distributions		0
Level 2 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	0	0
Corporate debt securities	1,519	4,744
U.S. government and federal agency securities	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading assets, excluding Investments at fair value based on NAV	857,441	1,314,065
Total available for sale securities	0	0
Cash and cash equivalents	0	0
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	0	0
Total trading liabilities	22,016	30,050
Other secured financings	268	544
Debt-structured notes	0
Level 3 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	38	38
Corporate debt securities	523	0
U.S. government and federal agency securities	0	0
Sovereign obligations	0	0
Loans	848	10,469
Derivatives	20,607	19,543
Level 3 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	22,195	40,906
Corporate debt securities	35,007	25,876
CDOs and CLOs	44,070	85,092
U.S. government and federal agency securities	0	0
Municipal securities	27,257	0
Sovereign obligations	0	120
Loans and other receivables	78,457	189,289
Derivatives	9,560	19,785
Investments at fair value	300,909	199,794
Investment in FXCM, Fair value of senior secured term loan receivable	207,400
Investment in FXCM, Fair value of senior secured term loan receivable and rights to future distributions		625,689
Level 3 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	0	0
Corporate debt securities	0	0
U.S. government and federal agency securities	0	0
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available for sale securities	21,868	23,240
Residential Mortgage-Backed Securities [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage-backed securities (4)		117
Residential Mortgage-Backed Securities [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	1,378,840	2,801,333
Residential Mortgage-Backed Securities [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	21,868	23,240
Residential Mortgage-Backed Securities [Member] | Level 1 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage-backed securities (4)		0
Residential Mortgage-Backed Securities [Member] | Level 1 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Residential Mortgage-Backed Securities [Member] | Level 1 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Residential Mortgage-Backed Securities [Member] | Level 2 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage-backed securities (4)		117
Residential Mortgage-Backed Securities [Member] | Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	1,331,959	2,731,070
Residential Mortgage-Backed Securities [Member] | Level 2 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	21,868	23,240
Residential Mortgage-Backed Securities [Member] | Level 3 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage-backed securities (4)		0
Residential Mortgage-Backed Securities [Member] | Level 3 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	46,881	70,263
Residential Mortgage-Backed Securities [Member] | Level 3 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available for sale securities	4,687	2,374
Commercial Mortgage-Backed Securities [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	345,505	1,029,239
Commercial Mortgage-Backed Securities [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	4,687	2,374
Commercial Mortgage-Backed Securities [Member] | Level 1 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Commercial Mortgage-Backed Securities [Member] | Level 1 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Commercial Mortgage-Backed Securities [Member] | Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	320,912	1,014,913
Commercial Mortgage-Backed Securities [Member] | Level 2 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	4,687	2,374
Commercial Mortgage-Backed Securities [Member] | Level 3 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	24,593	14,326
Commercial Mortgage-Backed Securities [Member] | Level 3 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Other Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available for sale securities	19,127	39,473
Other Asset-Backed Securities [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	177,500	161,554
Other Asset-Backed Securities [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	19,127	39,473
Other Asset-Backed Securities [Member] | Level 1 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Other Asset-Backed Securities [Member] | Level 1 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	0	0
Other Asset-Backed Securities [Member] | Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	116,388	118,629
Other Asset-Backed Securities [Member] | Level 2 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	19,127	39,473
Other Asset-Backed Securities [Member] | Level 3 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	61,112	42,925
Other Asset-Backed Securities [Member] | Level 3 [Member] | Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	$ 0	$ 0