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Collateralized Transactions (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Disclosure Collateralized Transactions [Abstract]
Customers, less allowance for doubtful accounts of $41 and $40 as of September 30, 2018 and December 31, 2017	$ 30,913	$ 29,821
Securities purchased under agreement to resell segregated for regulatory purposes	$ 8,700	$ 9,200
Percentage of securities repledged and deposited for customers	97.00%	82.00%

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Margin loans to clients stated net of allowance for doubtful accounts.

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Percentage of securities acquired through agreements to resell that are shown as repledged and have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.

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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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