Segment, Geographic and Revenue Information - Institutional Securities - Investment Banking Revenues (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue from External Customer [Line Items]
Investment banking	$ 1,635	$ 1,567	$ 4,467	$ 4,994
Institutional Securities \| Operating Segments
Revenue from External Customer [Line Items]
Investment banking	1,535	1,459	4,158	4,671
Institutional Securities \| Operating Segments \| Advisory
Revenue from External Customer [Line Items]
Investment banking	550	510	1,462	1,702
Institutional Securities \| Operating Segments \| Underwriting
Revenue from External Customer [Line Items]
Investment banking	$ 985	$ 949	$ 2,696	$ 2,969

Includes (1) underwriting revenue (the spread between the resale price received and the cost of the securities and related expenses) generated through the purchasing, distributing and reselling of new issues of securities (alternatively, could be a secondary offering of a large block of previously issued securities); and (2) fees earned for mergers, acquisitions, divestitures, restructurings, and other types of financial advisory services.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(b),(d))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration