Fair Value Disclosures (Schedule Of Assets And Liabilities Measured On Recurring Basis At Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value based on NAV	$ 24,200	$ 24,300
Derivatives	200,016
Counterparty/cash-collateral netting, Assets	(2,826,763)	(4,255,998)
Total trading assets, excluding investments at fair value based on NAV	14,582,268	14,960,928
Total available for sale securities	462,503	301,049
Derivatives	396,477
Counterparty/cash-collateral netting, Liabilities	(2,794,432)	(4,229,213)
Total trading liabilities	8,763,993	8,388,619
Other secured financings	34,187	41,768
Long-term debt - structured notes	310,057	248,856
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	705,313	857,337
Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	1,501,329	1,610,667
Corporate debt securities	1,545,468	1,718,947
U.S. government and federal agency securities	841,725	976,497
Sovereign obligations	2,986,470	2,629,344
Loans	1,492,524	802,355
Derivatives	396,477	650,809
Counterparty/cash-collateral netting, Liabilities	(2,794,432)	(4,229,213)
Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	2,727,889	2,637,555
Corporate debt securities	2,455,947	2,700,025
CDOs and CLOs	85,253	108,660
U.S. government and federal agency securities	1,153,045	2,446,123
Municipal securities	740,658	735,726
Sovereign obligations	2,819,227	2,423,048
Loans and other receivables	1,782,399	1,639,105
Derivatives	200,016	371,078
Counterparty/cash-collateral netting, Assets	(2,826,763)	(4,255,998)
Investments at fair value	307,830	314,359
FXCM term loan	132,800	164,500
Available For Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	95,545	79,425
Corporate debt securities	179	179
U.S. government and federal agency securities	293,142	174,933
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	5,256,166	6,348,755
Total available for sale securities	388,687	254,358
Total trading liabilities	3,818,718	3,948,201
Other secured financings	0	0
Long-term debt - structured notes	0	0
Level 1 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	1,468,429	1,593,548
Corporate debt securities	0	0
U.S. government and federal agency securities	841,725	976,497
Sovereign obligations	1,500,854	1,375,590
Loans	0	0
Derivatives	7,710	2,566
Level 1 [Member] | 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	99,900
Level 1 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	2,620,350	2,522,977
Corporate debt securities	0	0
CDOs and CLOs	0	0
U.S. government and federal agency securities	1,124,343	2,389,397
Municipal securities	0	0
Sovereign obligations	1,506,428	1,432,556
Loans and other receivables	0	0
Derivatives	5,045	3,825
Investments at fair value	0	0
FXCM term loan	0	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	95,545	79,425
Corporate debt securities	0	0
U.S. government and federal agency securities	293,142	174,933
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	11,430,589	12,072,393
Total available for sale securities	73,816	46,691
Total trading liabilities	7,726,506	8,658,547
Other secured financings	34,100	41,350
Long-term debt - structured notes	310,057	248,856
Level 2 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	32,576	16,806
Corporate debt securities	1,544,945	1,718,424
U.S. government and federal agency securities	0	0
Sovereign obligations	1,485,616	1,253,754
Loans	1,491,488	801,977
Derivatives	3,171,881	4,867,586
Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	86,959	92,839
Corporate debt securities	2,422,480	2,675,020
CDOs and CLOs	39,899	54,306
U.S. government and federal agency securities	28,702	56,726
Municipal securities	714,104	708,469
Sovereign obligations	1,312,799	990,492
Loans and other receivables	1,729,227	1,557,233
Derivatives	3,016,829	4,616,822
Investments at fair value	0	0
FXCM term loan	0	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	179	179
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	722,276	795,778
Total available for sale securities	0	0
Total trading liabilities	13,201	11,084
Other secured financings	87	418
Long-term debt - structured notes	0	0
Level 3 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	324	313
Corporate debt securities	523	523
U.S. government and federal agency securities	0	0
Sovereign obligations	0	0
Loans	1,036	378
Derivatives	11,318	9,870
Level 3 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equity securities	20,580	21,739
Corporate debt securities	33,467	25,005
CDOs and CLOs	45,354	54,354
U.S. government and federal agency securities	0	0
Municipal securities	26,554	27,257
Sovereign obligations	0	0
Loans and other receivables	53,172	81,872
Derivatives	4,905	6,429
Investments at fair value	307,830	314,359
FXCM term loan	132,800	164,500
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	34,828	19,133
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	1,439,474	999,266
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	34,828	19,133
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 Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage- and asset-backed securities, assets	1,400,215	960,494
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	34,828	19,133
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	39,259	38,772
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	10,446	8,337
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	586,147	316,985
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	10,446	8,337
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	565,494	296,405
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	10,446	8,337
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	20,653	20,580
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	28,363	19,042
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	151,583	104,498
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	28,363	19,042
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	113,881	63,587
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	28,363	19,042
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	37,702	40,911
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