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Collateralized Transactions (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Disclosure Collateralized Transactions [Abstract]
Customers, less allowance for doubtful accounts of $40 and $97 as of December 31, 2017 and 2016	$ 29,821	$ 19,409
Securities purchased under agreement to resell segregated for regulatory purposes	$ 9,200	$ 11,000
Percentage of securities repledged and deposited for customers	82.00%	99.00%

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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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