Securitization Activities - Firms Continuing Involvement in Securitization Entities to Which Firm Sold Assets (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Transfers and Servicing of Financial Assets [Abstract]
Fair Value of Retained Interests	$ 3,850	$ 3,350

Fair value portion of interest continued to be held by a transferor after transferring financial assets to a third party.

No definition available.

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