Collateralized Agreements and Financings - Financial Instruments Received as Collateral and Repledged (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Collateralized Agreements And Financings [Abstract]
Financial instruments at fair value received as collateral by the firm that it was permitted to deliver or repledge	$ 745,992	$ 661,490
Financial instruments at fair value received as collateral which the firm delivered or repledged	$ 604,615	$ 558,634

Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Name:	us-gaap_FairValueOfSecuritiesReceivedAsCollateralThatHaveBeenResoldOrRepledged
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant