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Financial Assets And Financial Liabilities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets and liabilities, transfers between levels, amount	$ 0	$ 0
Securities purchased under agreement to resell segregated for regulatory purposes	14,600	11,400
Total financial instruments owned, at fair value	1,327	2,119
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	3	$ 3
Level 3 | Corporate And Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	$ 3

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- Definition

Fair Value Assets And Liabilities, Transfers Between Levels, Amount

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- Definition

The carrying value of funds, segregated for regulatory purposes and for the exclusive benefit of customers, outstanding loaned in the form of security resale agreements if the agreement requires the purchaser to resell the identical security purchased or a security that meets the definition of "substantially the same" in the case of a dollar roll. Also includes purchases of participations in pools of securities that are subject to a resale agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

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