Derivative Financial Instruments (Fair Value And Related Number Of Derivative Contracts Categorized By Predominant Risk Exposure) (Details) $ in Thousands	Sep. 30, 2018 USD ($) Contract	Dec. 31, 2017 USD ($) Contract
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 3,523,745	$ 3,497,969
Fair Value, Liabilities	4,170,251	3,745,908
Net Amounts in Consolidated Statements of Financial Condition	189,645	179,488
Net Amounts in Consolidated Statements of Financial Condition	715,763	255,394
Rule change impact, derivative asset	189,645	179,488
Rule change impact, derivative liability	715,763	255,394
Designated as Accounting Hedges \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 0	$ 0
Number of Contracts, Assets \| Contract	0	0
Fair Value, Liabilities	$ 30,018	$ 2,420
Number of Contracts, Liabilities \| Contract	1	1
Not Designated as Accounting Hedges
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 3,523,745	$ 3,497,969
Fair Value, Liabilities	4,140,233	3,743,488
Counterparty/cash-collateral netting, Assets	(3,334,100)	(3,318,481)
Counterparty/cash-collateral netting, Liabilities	(3,454,488)	(3,490,514)
Net Amounts in Consolidated Statements of Financial Condition	189,645	179,488
Net Amounts in Consolidated Statements of Financial Condition	685,745	252,974
Not Designated as Accounting Hedges \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 766,233	$ 1,717,058
Number of Contracts, Assets \| Contract	20,867	38,941
Fair Value, Liabilities	$ 892,562	$ 1,708,776
Number of Contracts, Liabilities \| Contract	38,331	12,828
Not Designated as Accounting Hedges \| Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 234,641	$ 366,541
Number of Contracts, Assets \| Contract	8,569	6,463
Fair Value, Liabilities	$ 223,565	$ 349,512
Number of Contracts, Liabilities \| Contract	7,486	4,612
Not Designated as Accounting Hedges \| Equity contracts
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 2,491,005	$ 1,373,016
Number of Contracts, Assets \| Contract	1,892,926	2,728,750
Fair Value, Liabilities	$ 2,987,654	$ 1,638,258
Number of Contracts, Liabilities \| Contract	1,836,128	2,118,526
Not Designated as Accounting Hedges \| Commodity contracts
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 4,599	$ 3,093
Number of Contracts, Assets \| Contract	6,331	7,249
Fair Value, Liabilities	$ 16,312	$ 5,141
Number of Contracts, Liabilities \| Contract	3,585	6,047
Not Designated as Accounting Hedges \| Credit contracts
Derivatives, Fair Value [Line Items]
Fair Value, Assets	$ 27,267	$ 38,261
Number of Contracts, Assets \| Contract	172	130
Fair Value, Liabilities	$ 20,140	$ 41,801
Number of Contracts, Liabilities \| Contract	76	191
Rule Change by London Clearing House \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Rule change impact, derivative asset		$ 800,000
Rule change impact, derivative liability		$ 800,000

Derivative, Fair Value of Derivative Asset, Amount Netting in Consolidated Statement of Financial Condition

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Derivative, Fair Value of Derivative Liability, Amount Netting in Consolidated Statement of Financial Condition

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The number of derivative instruments of a particular derivative asset or group of derivative assets held by the entity.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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