Fair Value Disclosures (Schedule Of Assets And Liabilities Measured On Recurring Basis At Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Trading assets, at fair value	$ 17,310,213	$ 15,492,572
Derivative assets	189,645	179,488
Counterparty and Cash Collateral Netting, assets	(3,334,100)	(3,318,481)
Available for sale securities, equity securities		88,486
Debt securities, available for sale securities	1,868,420	628,075
Available-for-sale Securities		716,561
Liabilities:
Trading liabilities, at fair value	9,479,213	8,454,965
Counterparty and Cash Collateral Netting, liabilities	(3,454,488)	(3,490,514)
Short-term borrowings		23,324
Long-term debt - structured notes	709,557	606,956
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	913,456	578,014
Level 1
Assets:
Trading assets, at fair value	7,968,625	5,791,641
Derivative assets	13,117	165,396
Available for sale securities, equity securities		88,486
Debt securities, available for sale securities	1,607,725
Available-for-sale Securities		641,291
Liabilities:
Trading liabilities, at fair value	5,141,271	4,618,008
Short-term borrowings		0
Long-term debt - structured notes	0	0
Level 2
Assets:
Trading assets, at fair value	12,031,299	12,369,954
Derivative assets	3,507,491	3,323,278
Available for sale securities, equity securities		0
Debt securities, available for sale securities	260,695
Available-for-sale Securities		75,270
Liabilities:
Trading liabilities, at fair value	7,769,540	7,307,269
Short-term borrowings		23,324
Long-term debt - structured notes	545,927	606,956
Level 3
Assets:
Trading assets, at fair value	644,389	649,458
Derivative assets	3,137	9,295
Available for sale securities, equity securities		0
Debt securities, available for sale securities	0
Available-for-sale Securities		0
Liabilities:
Trading liabilities, at fair value	22,890	20,202
Short-term borrowings		0
Long-term debt - structured notes	163,630	0
Fair Value Measured at NAV
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative investments	399,032	590,104
Corporate equity securities
Assets:
Trading assets, at fair value	3,757,540	3,058,033
Liabilities:
Trading liabilities, at fair value	2,223,245	1,753,437
Corporate equity securities | Level 1
Assets:
Trading assets, at fair value	3,635,288	2,975,463
Liabilities:
Trading liabilities, at fair value	2,221,325	1,721,267
Corporate equity securities | Level 2
Assets:
Trading assets, at fair value	72,569	60,300
Liabilities:
Trading liabilities, at fair value	1,507	32,122
Corporate equity securities | Level 3
Assets:
Trading assets, at fair value	49,683	22,270
Liabilities:
Trading liabilities, at fair value	413	48
Corporate debt securities
Assets:
Trading assets, at fair value	2,507,682	3,287,336
Liabilities:
Trading liabilities, at fair value	1,513,536	1,689,347
Corporate debt securities | Level 1
Assets:
Trading assets, at fair value	0	0
Liabilities:
Trading liabilities, at fair value	0	0
Corporate debt securities | Level 2
Assets:
Trading assets, at fair value	2,498,031	3,261,300
Liabilities:
Trading liabilities, at fair value	1,511,979	1,688,825
Corporate debt securities | Level 3
Assets:
Trading assets, at fair value	9,651	26,036
Liabilities:
Trading liabilities, at fair value	1,557	522
Collateralized debt obligations and collateralized loan obligations
Assets:
Trading assets, at fair value	116,320	181,350
Collateralized debt obligations and collateralized loan obligations | Level 1
Assets:
Trading assets, at fair value	0	0
Collateralized debt obligations and collateralized loan obligations | Level 2
Assets:
Trading assets, at fair value	82,339	139,166
Collateralized debt obligations and collateralized loan obligations | Level 3
Assets:
Trading assets, at fair value	33,981	42,184
U.S. government securities
Assets:
Trading assets, at fair value	3,046,694	1,308,673
Debt securities, available for sale securities	1,607,725	552,805
Liabilities:
Trading liabilities, at fair value	1,398,222	1,430,737
U.S. government securities | Level 1
Assets:
Trading assets, at fair value	3,000,805	1,269,230
Liabilities:
Trading liabilities, at fair value	1,398,222	1,430,737
U.S. government securities | Level 2
Assets:
Trading assets, at fair value	45,889	39,443
Liabilities:
Trading liabilities, at fair value	0	0
U.S. government securities | Level 3
Assets:
Trading assets, at fair value	0	0
Liabilities:
Trading liabilities, at fair value	0	0
Municipal securities
Assets:
Trading assets, at fair value	749,616	710,513
Municipal securities | Level 1
Assets:
Trading assets, at fair value	0	0
Municipal securities | Level 2
Assets:
Trading assets, at fair value	749,616	710,513
Municipal securities | Level 3
Assets:
Trading assets, at fair value	0	0
Sovereign obligations
Assets:
Trading assets, at fair value	1,989,334	2,417,459
Liabilities:
Trading liabilities, at fair value	2,483,137	2,173,635
Sovereign obligations | Level 1
Assets:
Trading assets, at fair value	1,319,415	1,381,552
Liabilities:
Trading liabilities, at fair value	1,513,237	1,216,643
Sovereign obligations | Level 2
Assets:
Trading assets, at fair value	669,919	1,035,907
Liabilities:
Trading liabilities, at fair value	969,845	956,992
Sovereign obligations | Level 3
Assets:
Trading assets, at fair value	0	0
Liabilities:
Trading liabilities, at fair value	55	0
Residential mortgage-backed securities
Assets:
Trading assets, at fair value	1,899,487	1,479,371
Debt securities, available for sale securities	146,678	34,561
Residential mortgage-backed securities | Level 1
Assets:
Trading assets, at fair value	0	0
Debt securities, available for sale securities	0	0
Residential mortgage-backed securities | Level 2
Assets:
Trading assets, at fair value	1,894,533	1,453,294
Debt securities, available for sale securities	146,678	34,561
Residential mortgage-backed securities | Level 3
Assets:
Trading assets, at fair value	4,954	26,077
Debt securities, available for sale securities	0	0
Commercial mortgage-backed securities
Assets:
Trading assets, at fair value	815,365	520,534
Debt securities, available for sale securities	15,719	5,870
Liabilities:
Trading liabilities, at fair value	70	105
Commercial mortgage-backed securities | Level 1
Assets:
Trading assets, at fair value	0	0
Debt securities, available for sale securities	0	0
Liabilities:
Trading liabilities, at fair value	0	0
Commercial mortgage-backed securities | Level 2
Assets:
Trading assets, at fair value	791,449	508,115
Debt securities, available for sale securities	15,719	5,870
Liabilities:
Trading liabilities, at fair value	0	0
Commercial mortgage-backed securities | Level 3
Assets:
Trading assets, at fair value	23,916	12,419
Debt securities, available for sale securities	0	0
Liabilities:
Trading liabilities, at fair value	70	105
Other asset-backed securities
Assets:
Trading assets, at fair value	333,272	278,240
Debt securities, available for sale securities	98,298	34,839
Other asset-backed securities | Level 1
Assets:
Trading assets, at fair value	0	0
Debt securities, available for sale securities	0	0
Other asset-backed securities | Level 2
Assets:
Trading assets, at fair value	263,967	217,111
Debt securities, available for sale securities	98,298	34,839
Other asset-backed securities | Level 3
Assets:
Trading assets, at fair value	69,305	61,129
Debt securities, available for sale securities	0	0
Loans and other receivables
Assets:
Trading assets, at fair value	1,504,481	1,667,885
Loans and other receivables | Level 1
Assets:
Trading assets, at fair value	0	0
Loans and other receivables | Level 2
Assets:
Trading assets, at fair value	1,455,496	1,620,581
Loans and other receivables | Level 3
Assets:
Trading assets, at fair value	48,985	47,304
Investments at fair value
Assets:
Trading assets, at fair value	326,977	330,890
Investments at fair value | Level 1
Assets:
Trading assets, at fair value	0	0
Investments at fair value | Level 2
Assets:
Trading assets, at fair value	0	946
Investments at fair value | Level 3
Assets:
Trading assets, at fair value	326,977	329,944
FXCM term loan
Assets:
Trading assets, at fair value	73,800	72,800
FXCM term loan | Level 1
Assets:
Trading assets, at fair value	0	0
FXCM term loan | Level 2
Assets:
Trading assets, at fair value	0	0
FXCM term loan | Level 3
Assets:
Trading assets, at fair value	73,800	72,800
Loans
Liabilities:
Trading liabilities, at fair value	1,145,240	1,152,310
Loans | Level 1
Liabilities:
Trading liabilities, at fair value	0	0
Loans | Level 2
Liabilities:
Trading liabilities, at fair value	1,136,579	1,148,824
Loans | Level 3
Liabilities:
Trading liabilities, at fair value	8,661	3,486
US Treasury securities
Assets:
Debt securities, available for sale securities	1,607,725	552,805
US Treasury securities | Level 1
Assets:
Debt securities, available for sale securities	1,607,725	552,805
Liabilities:
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	34,800	99,700
US Treasury securities | Level 2
Assets:
Debt securities, available for sale securities	0	0
US Treasury securities | Level 3
Assets:
Debt securities, available for sale securities	0	0
Derivatives
Liabilities:
Trading liabilities, at fair value	715,763	255,394
Counterparty and Cash Collateral Netting, liabilities	(3,454,488)	(3,490,514)
Derivatives | Level 1
Liabilities:
Trading liabilities, at fair value	8,487	249,361
Derivatives | Level 2
Liabilities:
Trading liabilities, at fair value	4,149,630	3,480,506
Derivatives | Level 3
Assets:
Derivative assets	3,137	9,295
Liabilities:
Trading liabilities, at fair value	$ 12,134	$ 16,041